最新刊期
卷 27 ， 期 5 ， 2006
- 摘要：Under the effective mass approximation, the internal excited state properties of the strong-coupling exciton in polar crystals quantum dot are studied by using linear combination operator and unitary transformation methods. The ground state energy, the first internal excited state energy and the excitation energy in the strong-coupling polar crystals quantum dot as a function of the quantum dot radius are obtained. Numerical calculations for TlCl crystal show that the ground state energy, the first internal excited state energy and the excitation energy of the strong-coupling exciton will increase strongly with the decreasing of the quantum dot radius.关键词：strong-coupling;exciton;internal excited state;linear combination operator112|94|2更新时间：2020-08-11
- 摘要：Analytical expressions of linear and third-order nonlinear optical refractive index changes are obtained in P schl-Teller well using the density matrix formalism taking into account the intrasubband relaxation. Since there are two adjustable parameters κ and λ in the P schl-Teller well, the shape of the wells will change with the change of the parameters κ and λ, accordingly the linear and the third-order nonlinear refractive index will change with the para meters κ and λ. It is shown that the refractive index changes depends on the shape of the well, the tunnel bandwidth and the optical power. Numerical results are presented for a typical GaAs/AlGaAs P schl-Teller well.关键词：P schl-Teller well;refractive index;density matrix approach110|144|2更新时间：2020-08-11
- 摘要：By applying a variational approach based on two successive canonical transformations and using a displaced-oscillator type unitary transformation to deal with bilinear terms,the influence of the dispersion of phonon on properties of magnetopolaron in a parabolic quantum dot (QD) is studied.The ground state energy and the average number of virtual phonons around the electron of weak-coupling magnetopolaron are calculated considering the in-fluence of the dispersion of phonon.Their dependence on the confinement length,the cyclotron frequency,the electron-LO-phonon coupling constant and the coefficient of phonon dispersion is depicted in the electron-LO-phonon weak-coupling case.关键词：the squeezed-state;quantum dot;phonon dispersion;magnetopolaron120|96|1更新时间：2020-08-11
- 摘要：The special structure of superlattice leads to strong interest from 1970’s,because it has the particular photo-electric characteristics.Along the development of the film technique,the component and the thinckness for the superlattice material can be controlled artificially,then gap engineering and doping engineering are formed.The well width can be regulated by means of controlling the thinckness of the film for the superlattice material;the well deep can be regulated also by means of controlling the component for the superlattice material.If the barrier layer of the multi-quantum well or superlattice was slight enough,the small size effect must consider.Of course,if the barrier layer of the multi-quantum well or superlattice was think enough,to such an extent as to the interaction between quantum wells can be neglected,the superlattice can be regarded as the single repeat of the single quantum well,then problem of multi-quantum well reduced to the problem of the single quantum well.Usual interaction potential is the squared potential well to describe the motion behaviour of an electron in the single quantum well.The new interaction potential with tan2x form is leaded.In the frame of quantum mechanics,equation to describe the particle motion is reduced to the hypergeometric equation by this potential.The energy eigenvalue and the eigenfunction problem of the equation are transformed to the eigenvalue and the eigenfunction problem of the hypergeometric equation.The eigenvalue and the eigenfunction of the system are calculated,and the distribution of level in quantum well are discussed.As an example,the level and the transition of an electron in the single quantum well for material Ga1-xAlxAs-GaAs-Ga1-xAlxAs are calculated.It shows that coincidence between the theory and the experiment is improved futher.关键词：superlattice;quantum well;hypergeometric equatin;single particle level;eigenvalue;eigenfunction119|88|1更新时间：2020-08-11
- 摘要：With the flying development of nanotechnology,the studies on the low dimension system have been greatly improved,especially on the nano semiconductor quantum dot.Since its newly opto-electric and transportation characteristics,it is becoming a heat field in the study of quantum fanctional device.Since 1980s,Tokuda has investigated the bounding polaron in the Coulombic field using LLP variational method.More and more people pay attention to the field of bounding polaron,which is not only bound by the hydrogen but also interact with LOphonon in the ionic crystal or polar semiconductor.Some anothers also use other kinds of methods to investigate the properties of bound polaron in quantum dot theoretically and expercmentally.The vibrational frequency,the ground state energy,the interaction en-ergy and the average number of optical phonons of the bound polaron in a quantum dot have been discussed using the linear combination operator method by the present authors.However,the influences of the temperature on the properties of bound polaron in a quantum dot has not been investigated so far.In fact,the case of a finite temperature is more significant.The influences of the temperature on the properties of weak-coupling bound polaron in a quantum dot are studied.The vibrational frequency,the ground state energy and the mean number of the phonons of the weak-coupling bound polaron in a quantum dot are derived by using the linear combination operator and the unitary transformation method.The temperature dependence of the vibrational frequency,the ground state energy and the mean number of the phonons of the weak-coupling bound polaron in a quantum dot are discussed.Nume-rical calculations,for the ZnS crystal as an example,are performed and the results indicate that the vibrational frequency,the ground state energy and the mean number of the phonons of the weak-coupling bound polaron in a quantum dot will increase with increasing the temperature.The ground state energy of bound polaron will increase strongly with increasing the confinement strength of the quantum dot.关键词：quantum dot;bound polaron;temperature dependence;coulombic potential96|111|0更新时间：2020-08-11
- 摘要：With the development of semiconductor growth technology,people have produced kinds of quantum dots.Due to the novel optoelectronic properties and the transport characteristics of quantum dots,there will be a widely applied prospect for them.Many investigators studied the properties of a quantum dot by means of various theoretical and experimental methods.In recent years,with the study of the properties of bound polaron in a quantum dot,people have paid more attention to them.Woggon et al.studied the states of polarons bound in a potential and determined the local optical absorption spectrum up to first-order time-dependent perturbation theory with respect to the electron-phonon interaction.Chen et al.derived the expression of the ground state energy of an electron coupled simultaneously with a coulomb potential and a longitudinal-optical phonon field in parabolic quantum dots and wires within the framework of Feynman variational path-integral theory.Xie et al.investigated the binding energy of a bound polaron in a spherical quantum dot by using the varia-tional method,and so on.However,few investigators studied the bound polaron in the quantum dot with the linear combination operator method so far.By using the linear combination operator and unitary transformation method,the properties of the bound polaron in a parabolic quantum dot are studied for the strong electron-phonon coupling case.Results show that the vibration frequency of the strong-coupling bound polaron in a parabolic quantum dot will increase strongly with decreasing the effective confinement length of quantum dot and increase with increasing the electron phonon coupling strength.The ground state energy of the strong-coupling bound polaron will increase strongly with decreasing the effective confinement length,and at the same value of the confinement length,the higher the coupling strength,the higher is the value of the ground state energy.The ground state energy of strong-coupling bound polaron change little with electron-phonon coupling strength for l0>0.30,whereas they change strongly with electron-phonon coupling strength for l0>0.30.The ground state energy of strong-coupling bound polaron will increase with increasing the coulomb bound potential.From the equation of the effective confinement length of the quantum dot l0=√E/mω0,we can see that the effective confinement length of quantum dot is reciprocal with the square root of the confinement strength ω0 of the quantum dot.Thus the vibration frequency and the ground state energy of strong-coupling bound polaron in a parabolic quantum dot will increase with increasing the confinement strength.关键词：parabolic quantum dot;strong-coupling;bound polaron111|110|0更新时间：2020-08-11
- 摘要：Organic light-emitting diode (OLED) has attracted considerable attention due to their unique image quality and market potentials in display application.For the full-color display applications,it is essential to deliver the primary RGBemitters with high luminous efficiency,saturated color chromaticity,among which 9,10-Di (2-naphthyl) anthracene (ADN) is one of the stable and pure blue emitters.However,little attention has been paid to the influences of ADN’s purification on the electroluminescent (EL) performance.Synthesis and purification of ADNwere studied.The photoluminescence (PL) and electroluminescence (EL) spectra of ADNsynthesized and purified are investigated,respectively.The PLspectrum of ADNpurified exhibits an emitting peak at 434 nm with a full-width at half-maxium (FWHM) of 54.2 nm,while the rough material without purification is red shifted to 436 nm with the same FWHMof 54.2 nm.Organic light-emitting diodes (OLEDs) with a structure of indium tin oxide (ITO) (100 nm)/N,N’-biphenyl-N,N’-bis-(1-naphenyl)-[1,1’-biphenyl]-4,4’-diamine (NPB) (40 nm)/ADN (30 nm)/tris (8-quinolinolate) aluminum (Alq3) (20 nm)/LiF (1 nm)/Al (100 nm) are fabricated,where the rough and purified ADNare used as emitting layers in DiodeⅠand in DiodeⅡ,respectively,NPBis used as hole transport layer,Alq3 as an electronic transport layer in this structure.Little diffe-rence of the maximum peak of ELspectra between two Diodes is found,which is 432 nm in DiodeⅠand 433 nm in DiodeⅡ,a current efficiency of 2.5 cd/Awith the Commission Internationale d’Eclairage (CIE) coordinates of (x=0.15,y=0.06) is got in DiodeⅡ while only a current efficiency of 1.5 cd/Awith CIEof (x=0.15,y=0.10) is found in DiodeⅠ.It is supposed that the purification of the ADNrough material has a positive effect on the ELcharacteristics of the OLED,meanwhile with fewer impacts on the PLspectra.Therefore the purification can be improved the performance of OLED greatly.121|121|0更新时间：2020-08-11
- 摘要：Inorganic semiconductor multiple quantum well structures have been a subject of intense study due to their interesting electronic and optical properties which have many promising applications in optoelectronic device technology.In the past decade,following organic semiconductor research,organic semiconductor multiple quantum well structures have been studied by many research groups.Organic crystals are bonded by relatively weak Van der Waals forces.Therefore,the potential exists for fabrication of high quality heterostructures or multilayer structures without inducing large strains using a variety of organic crystalline materials.In this paper,quantum well structures consisting of alternating layers of organic 4,4’-N,N’-dicarbazole-biphenyl (CBP)/8-hydroxyqunoline aluminum (Alq3) have been grown by organic molecular beam deposition.Energy level,structure and optical property of the quantum well are determined by cyclic voltammetry,optical absorption,small angle X-ray diffraction and photoluminescence.Cyclic voltammetry and optical absorption results indicate that the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) levels of CBPare-2.74 and-6.00 eV,and those of Alq3 are-3.10 and-5.80 eV,respectively.It is clear that the CBP/Alq3 multilayers possess the energy lineup which can be classified as Type-Ⅰ,where the HOMO of Alq3 is higher than that of CBPand the LUMO of Alq3 is lower than that of CBP.The quantum well structure exhibits clear high-order Bragg peaks by small angle X-ray diffraction measurements and this indicates the structure of the quantum well is precisely ordered.The PLexperimental results indicate that the structures of CBP/Alq3,possessing a Type-Ⅰ energy lineup,exhibit the rapid energy transfer from CBP to Alq3,and lead to the increase of Alq3 PLintensity.The PLpeaks of Alq3 shift to higher energy as the Alq3 layer thickness is decreased.The origin of the peak emission energy blue shift is discussed with the theoretical and experimental results published in the literatures.关键词：organic quantum well structure;photoluminescence124|93|1更新时间：2020-08-11
- 摘要：Improvement of the triple colors,red,green and blue is the most basic and the most important technology for full color display.Green and blue emission from the organic light emitting diodes (OLED) have been employed successfully to organic display,but the red light performance still need to improved.So far,host-guest system and rare earth complexes were used for red emission.In these two kinds of OLEDs,the energy transfer efficiency were generally limited by the concentration quenching and the phase separation.Ones have paid great effort to explore some novel materials and devices structures for red emission with high perfor-mance.In this paper,an ionic organic pyridyl salt [ASPT (trans-4-[P-(N-ethyl-N-(hydroxylethyl)-amino) styryl]-N-methylpyridinium tetraphenyl-borate) ] was employed as active layer for an organic light-emitting diode with stable red emission.The investigation on the electroluminescent properties demonstrated that ASPTis a good luminescent molecule for red emission.Astable red electroluminescence was obtained by using this material as emitting layer in a monolayer structure.The luminescence mechanism was discussed based on the influence of the external electrical field on the energy barrier in the interfaces between the active layer and the electrodes.In order to understand the charier charge transport and their recombination process,and to improve the ELperformance,double-layer TPD/ASPTor ASPT/Alq3 and triple-layer TPD/ASPT/Alq3 structures were designed and the ELproperties were further studied.Brighter red ELand red-blue variable emission depended on the applied voltage were observed in the double-layer and the triple-layer structures,respectively.Consi-dering the different function of each layer in the triple-layer structure,the color variation is assumed to the change of the recombination region.The mechanism was discussed by analyzing the spectra and the corresponding energy level structures.关键词：organic salt;red emission;spectral variation105|73|2更新时间：2020-08-11
- 摘要：Polymer light-emitting diodes (PLEDs) have attracted great attention in recent years due to their potential advantages in fabrication,mechanical properties,and low cost.Balance of charge injection and transporting is a key factor that determines device performances such as efficiency and operating lifetime.Usually,carrier-transporting layer or block layer was inserted into the device to improve the balance of the injected carriers.In this paper,PLEDs with different thickness of luminescent layer were fabricated.The conjugated polymer poly (2-methoxy,5-(2-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) was used as a luminescent layer.By blending PBDinto the luminescent layer in different concentration,comparing and analysising their properties of Current density-voltage (J-V) and Luminance-efficiency-voltage (L-E-V),we found that the PBDnot only enhanced the transporting of the electrons but also blocked the injection of the holes and leading to a better balance of the carriers,which improves the performances of PLEDs.The optimum concentration of the PBDwas found to be 20%.ELemissions of blend devices were red-shifted by about 7 nm from the peak emission at 589 nm of pure MEH-PPVdevice to around 596 nm of devices with the blend film as EML (emission layer).The Full width at half maximum (FWHM) was narrowed from 100 nm to 44 nm.关键词：polymer light-emitting diodes;PBD;hole blocking140|97|0更新时间：2020-08-11
- 摘要：Full color display is the goal of organic light-emitting diode (OLED),but the making of stable red devices is the great barrier in the mass production of OLED,and is also the most interesting field nowadays.In order to use organic light-emitting diodes in display,it is very important to obtain red emitting light.There are two methods for getting it:doping high fluorescent dyes in host materials or using metal complexes.Phosphorescent dyes have been efficiently used so far.Now some red organic light-emitting diodes have been realized by doping the dye rubrene with different dopant concentrations in light-emitting layers.We demonstrate red organic light-emitting diodes with the electroluminescent layers consisting of tris (8-hydroxyquinoline) aluminum (Alq3) doped with the dye DCJTBand rubrene,which the emission efficiency depends on the concentrations of DCJTBand rubrene.The typical cell structure is as follows:[ITO/CuPc/NPB/Alq3:rubrene:DCJTB/Alq3/LiF/Al],where N,N’-bis-(1-napthyl)-N,N’-diphenyl-1,1’-biphenyl-4,4’-diamine (NPB) and Alq3 are used respectively as the hole transporting layer and electron transporting layer.It is found that the luminence efficiency of the devices in which DCJTBand rubrene were properly doped is twice to three times that of those doped only with DCJTB.The emission of guest in doped organic light emitting diodes may result from either energy transfer from host,carrier trapping or both mechanisms.In order to understand the energy transport mechanism between host and guest materials,we use the Frster theory and energy band to explain it,and found that the main energy mechanism of dopant emission in the doped red OLEDis not the Frster energy transfer,but the sequential carrier trapping,and that rubrene can assist the energy transfer from Alq3 to DCJT Bmore efficiently,which greatly improved the luminence efficiency and performances of devices.关键词：organic light-emitting diode(OLED);energy transfer;F rster theory;carrier trapping111|67|3更新时间：2020-08-11
- 摘要：Organic light emitting diodes (OLED) employing an Ir complex with coumarin (C6) and acetylacetone (acac) ligands Ir (C6) 2 (acac) are studied.This novel Ir complex can be used both as electron transporting material and light emitting dopant.Comparing the photoluminescence spectra of solid C6 and Ir (C6) 2-(acac),the self-quenching effect of molecules was found to be suppressed obviously.To a device structure of ITO (indium tin oxide)/TPD (N,N’-diphenyl-N,N’-bis (3-methyl-phenyl)-1,1’biphenyl-4,4’diamine)/Ir (C6) 2 (acac)/BAlq (bis (2-methyl-8-quinolinolato-N1,O8)-(1,1’-biphenyl-4-olato) aluminum)/Alq3 (tris-(8-hydroxy-quinoline) aluminum)/Liq (8-hydroxyquinoline lithium)/Al,an orange color (Commission Interationale d’Eclairage (CIE) coordinates x=0.43;y=0.40) with a max luminance of 3390 cd/m2 and an efficiency of 1.3 cd/A (quantum efficiency 1.3%) are achieved.Using Ir (C6) 2 (acac) as dopant and Alq3 as electron transporting host with the same structure,a green color (CIEcoordinates x=0.29;y=0.58) and a max luminance of 8832 cd/m2 and an efficiency of 5.6 cd/A (quantum efficiency 1.5%) are obtained.Mechanism of luminescence shows that the orange color luminescence of the device using Ir (C6) 2 (acac) as light-emitting layer origins from the triplet emission of Ir (C6) 2 (acac) dominantly;the green color luminescence of the other device origins from the fluorescence of Alq3,Ir (C6) 2 (acac),and a little phosphorescence of Ir (C6) 2 (acac).关键词：organic electrophosphorescence;OLED115|113|0更新时间：2020-08-11
- 摘要：Electrophosphorescent light-emitting diodes,for which both singlet and triplet excitons contribute to the light emission,have attracted great scientific and commercial attention because of their high quantum efficiency.Iridium-based complexes are the popular selection as the efficient dopant due to a relatively short phosphorescent lifetime.The electrophosphorescent polymers with iridium complex as a repeat unit incorporated into a conjugated main chain were investigated.In this case,the conjugated segments play the roles:a polymer ligand and a host for the energy transfer system.In this kind of phosphorescent polymers,the position and angle will affect the light wavelength and light efficiency of the PLEDbased on them.We demonstrated the efficient synthesis of the copolymers with Ir complexes incorporated onto fluorene-alt-carbazole backbone by Suzuki polycondensation via brominated iridium (Ⅲ) bis (1-phenylisoquinolyl-N,C2’) acetylactonate.With the different feed ratio from 0.1% to 0.5%,four polymers,named by PFCzIrPiq 01,PFCzIrPiq 02,PFCzIrPiq 03,and PFCzIrPiq05,were synthesized respectively.The resultant copolymers are easily soluble in common solvents such as toluene,tetrahydrofuran and chloroform,which provides for the facility in preparation of the polymer films by spin coating.The maximum external quantum efficiency of 2.8% and luminescent efficiency of 1.3 cd/Awere obtained from the device fabricated with copolymer PFCzIrPiq05.It indicates that the introducing complexes onto polymer backbone may be a better way to improve the efficiency of phosphorescent polymers in light-emitting diodes.关键词：electrophosphorescence;iridium complex;fluorene-alt-carbazole copolymer102|78|1更新时间：2020-08-11
- 摘要：Temperature plays an important role on the characteristic of the organic light-emitting devices,such as it can change the carriers mobility,and influence on the device’s current,luminescence efficiency,lifetime and so on.So adequate understanding of the temperature characteristic of the organic light-emitting device is more needed and important,but the study about it is still insufficient.Sksaha,Feller and Ashok have studied the temperature characteristics of organic light-emitting devices by experimental and theoretical methods,but those works are not sufficient to adequately understand the temperature influence on the properties of organic light-emitting devices.Fowler-Nordhein tunneling and thermionic emission are the dominant mechanisms of current injection at metal/organic interfaces,and the former can be ignored at low-field,so injection current nearly equals to thermionic emission current.After taking the injection limited (IL) and bulk limited (BL) current into consideration at the same time on the condition of non-ohmic injection contact and low-field operation,using numerical methods the temperature influence on the device’s J-Vcharacteristic,the carrier density and the filed distribution in the organic layer were studied.Results show that device current will increase as the temperature increasing at a given voltage,and that the J-Vcharacteristic curve become stepper in the higher temperature than that in the lower temperature.Carrier density and its distribution grads in organic layer will increase as the temperature increasing at a given voltage.Field distribution grads increases as the temperature increasing in the organic layer,and the current conduction will approach to be bulk limited (BL).Field distribution grads decrease as the temperature decreasing in the organic layer at a given voltage,and the field intensity through organic layer will approach to U/d,with U the bias,and d the organic film thickness,the current conduction will approach to be injection limited (IL).The results have a good agreement with the experi-mental data when using proper parameters.关键词：temperature;low field;single layer device;numerical study112|254|0更新时间：2020-08-11
- 摘要：Electrophosphorescent light-emitting diodes,for which both singlet and triplet excitons contribute to the light emission,have attracted great scientific and commercial attention because of their high quantum efficiency.Iridium-based complexes are the popular selection as the efficient dopant due to a relatively short phosphorescent lifetime.Aseries of electrophosphorescent conjugated polymers based on substituted para-polyphenylenes are synthesized by Suzuki polycondensation.Apart of N-alkyl benzene units were replaced by di-ketone group ended to provide a ligand for the formation of Ir complexes in side chain in the presence of 2-phenylpyridine.Poly (para-phenylene) with broad band gap makes the energy level better matching between the host and the guest.Therefore,energy transfer from the host to Ir-complex becomes more efficient.The incorporation of long alkoxy group into the side-chain can substantially raise the flexibility of polymer that leads to the improvement of solubility of polymer,which is helpful for the fabrication of devices.On the other hand,the activity of β-diketone group to iridium core is raised due to more rotating freedom of β-diketone-alkyl around the oxygen atom.ELemission from the backbone of the polymers is completely quenched even though the feed content ratio of Ir-complex is as low as 1%.They all show only the emission from iridium complex,while the host emission disappeared.It indicates that efficient energy transfer from the main chain to the Ir-complex occurs.The maximum external quantum efficiency of 2.6% was achieved for PPPIrPPy2 with the feed content ratio of Ir-complex of 2% at the current density of 0.35 mA/cm2.关键词：poly(para-phenylene);iridium complex;electrophosphorescence100|95|0更新时间：2020-08-11
- 摘要：It has been demonstrated that phenothiazine unit (M2) is a excellent p-type building block for lowering IP (ionic potential) of conjugated polymers due to its readily injection and transport of hole.Unlike phenothiazine,phenothiazine-5-oxide (M3) is a specific molecular which may be a good electron transporting unit due to the conversion of electron-donating sulfur atom to electron-withdrawing sulfoxide group.M3 was synthesized successfully through five-step reaction including: (1) nucleophilic substitution alkylation of initial material phenothiazine, (2) Vilsmeier reaction of the above product, (3) protection of aldehyde group, (4) oxidation of sulfur to sulfoxide and (5) hydrolysis of acetal.Using the hole transport property of M2 and the electron transport property of M3,we synthesize a high efficient electroluminescent polymer[P1],meantime the two units have the nonplanarity charateristic of molecular structures which can impede π-stacking aggregation and intermolecular excimer formation to improve the quantum efficience of P1.Aflexible long chain is fused on the phenothiazine ring to improve the solubility of polymer in furan,chloroform,toluene.To investigate the effect of electron-withdrawing of phenothiazine-5-oxide on the electron transport characteristic,polymer (P2) which doesn’t contain phenothiazine-5-oxide unit is synthesized with the same method as P1.For comparison,P1 and P2 are fabricated into single layer devices,and the external quantum efficiency of P1 device is 2.5 times more than that of P2 device.It implies that the introduction of M3 effectly improve the luminescent efficiency of P1.关键词：PLED;phenothiazine;electron transport110|161|1更新时间：2020-08-11
- 摘要：With poly (N-vinylcarbazole) (PVK) layer used as hole transport layer (HTL),influence of thickness of PVKlayer on indium tin oxide (ITO)/PVK/tris-(8-hydroxyquinoline) aluminum (Alq3)/Mg:Ag/Al double-layer (DL) device’s performance was investigated.Measurements showed that when the thickness of Alq3 was fixed to be 50 nm,the device with 18 nm PVK HTLhas the best performance of light emission,e.g.,the lowest turn-on voltage,the highest brightness and efficiency.Differences between these PVK DLdevices and N,N’-bis-(1-naphthyl)-N,N’-diphenyl-(1,1’-biphenyl)-4,4’-diamine (NPB)/Alq3 DLdevices’ lifetime were compared.Results showed that the device with thickest PVKlayer has the longest lifetime.The different lifetime between PVKand NPB DLdevice originated from the differences between fabrication techniques and energy band structure of the two HTLs.关键词：organic electroluminescent device;poly(N-vinylcarbazole);hole transport layer;device performance142|117|0更新时间：2020-08-11
- 摘要：Anovel red emitting phosphor α-Gd2 (MoO4)3:Eu3+ was prepared by solid-state reaction,using the NH4Fas the flux.The effects of flux content and concentration of activator on the crystal structure,mor-phology and luminescent properties were investigated by using XRD,SEM,and fluorescent spectra.The XRD patterns showed that the resultants have the monoclinic phase,and with the increase of the flux amount the crystallization could be improved greatly.The SEM images indicate that the morphology of the phosphor particle is close to ball-like,and thier mean size is around 2 μm.It is also observed that higher flux amount could result in agglomeration of phosphor particles.These results suggest that proper amount of flux should be around 3%.The excitation spectra show effective absorption wavelengths at ultraviolet (UV) (395 nm) and blue (465 nm) corresponding to the f-f transition of Eu3+.These wavelengths coincide with the wavelengths of commercial GdN based LED,so that the phosphor may be a better candidate for red component for white LED.The emission spectra exhibit most intense emission at 613 nm,which is assigned to the5D0→7F2 transition.The intense electric dipole transition implies that the Eu3+ occupies non-centrosymmetric sites in the matrix.The dependence of emission intensity on the flux was investigated.The better choice for introducing flux was confirmed to be at 3%,which is in a good agreement with the result derived from the XRD and SEM.Higher quenching concentration was showed to be 40% by studying the dependence of luminescent intensity on the Eu3+ concentration.关键词：Gd2(MoO4)3;white LED;phosphor110|138|12更新时间：2020-08-11
- 摘要：Lu2Si2O7:Ce crystal is a recently discovered inorganic scintillator.It is suitable for applications such as PETor oil well logging.Transparent and crackless LPS:Ce crystals have been grown by using the Czochralski method in our lab.We have characterized the scintillation properties of cerium doped lutetium pyrosilicate and discussed its luminescent mechanism.Alot of work has been done on the temperature dependence of the emission spectra under UVexcitation and the temperature dependence of the fluorescence lifetimes using a Edinburgh-920 luminescence spectrometer,which will help us to find the optimal working temperature for this crystal.Transmission spectra shows that the absorption cut-off edge of LPS:Ce crystal is 25 nm shorter than LSO:Ce crystal,which widens the transmission range.X-ray induced emission spectra are characteristic of two peaks and the main peak locates at 378 nm,which are consistent with the emission spectra under UVexcitation.The temperature dependence of the emission spectra under UVexcitation shows two features,the first is luminescence efficiency decreasing strongly when the temperature beyond 375 K,and the second is peak site red shifting when the temperature beyond 425 K.Decay curve follows the single exponential decay law.The decay time is about 34 ns at room temperature under UVexcitation.Based on the shapes of the decay curves,two distinct trends are identified.First,below 375 K,the curves are similar to that obtained at room temperature,and the fitting results vary from 32.8 ns to 34 ns.There is a little difference,but it is stable on the whole.In this range,the decay time slightly increases with temperature.Second,beyond 375 K,temperature dependence of the fluorescence lifetimes becomes evident,for example,with the increases of the temperature,the decay time strongly decreases.The decay time shorten to 6.72 ns at 500 K.Luminescence efficiency seems connected to decay time,and they change towards the same direction.Two peaks can be observed in TLcurves,approximately situated at 488 and 553 K.Both of them are far above room temperature.No TLglow peaks near room temperature,is suggested to be related to the absence of afterglow in LPS:Ce crystal.关键词：scintillation properties;LPS:Ce crystal;transmission spectra;decay curve111|65|2更新时间：2020-08-11
- 摘要：Two kinds of europium-substituted Keggin type polyoxometalates of BPOM:Eu and ZrPOM:Eu have been synthesized,which are highly luminescent.Their Keggin type structure has been characterized by IRand XRDspectra.The emission and excitation spectra have been measured at room temperature.The emission spectra show Eu gives strong emission in red light region,but the magnetic dipole transition5D0→7F1 domains others in BPOM:Eu;while a hypersensitive electric dipole transition5D0→7F2 domains others in ZrPOM:Eu.The5D0→7F1 and5D0→7F2 transitions are extremely sensitive to the chemical surroundings in the vicinity of the Eu3+ ions.The5D0→7F2 transition is not only permissive in asymmetry environment but also is of hypersensitive forbidden transition which is extremely sensitive to the chemical surroundings in the vicinity of the Eu3+ ions.When the Eu3+ ions’ sites hold asymmetry centers,the5D0→7F2 transition of Eu3+ ions is permissive while in symmetrical environment the5D0→7F1 transition is permissive.Judged from the spectra results the Eu site symmetry in BPOM:Eu surpasses that in ZrPOM:Eu.This contrast stems from different nature (radius and polarative ability) of the boron and zirconium heteroatoms.The site difference also influnce on Eu3+ ions’ excitation spectra.The spectrum of ZrPOM:Eu has four main groups of peaks:the highest peak laying at 395 nm,the others laying at 381～385 nm,464 and 535 nm with similar intensity.The spectrum of BPOM:Eu has two main groups of peaks:the highest peak lying at 395 nm,the second highest peak laying at 381～385 nm,the others are very weak.There exits energy transfer among Eu3+ ions.Resonant transfer is important ways for lanthanide especially the same kinds of lanthanide ions due to more spectra overlapping.This function leads to typical fluorescence quenching,the maximum intensity lies at Eu concentration of 2.0% in BPOM:Eu and at Eu concentration of 2.4% in ZrPOM:Eu respectively.There exist two characteristic absorption bands of Keggin anions at nearly 200 and 260 nm in ultraviolet region ascribeed to Od→W charge transition.There may exist possibility of energy transfer within short distance.There exists low intramolecular energy transfer from the excited Od→W charge transition to Eu3+ in ZrPOM :Eu,but doesn’t in BPOM:Eu at room temperature.关键词：Keggin structure;polyoxometalates;photoluminescence;rare earth doping108|52|0更新时间：2020-08-11
- 摘要：FEDdevices operate at much lower accelerating voltages,so the driving currents have to be greatly increased to maintain adequate brightness.Surface degradation of the phosphor occurs due to reaction with residual gases in the vacuum,and this is exacerbated by the higher current density.This degradation leads to decrease brightness of screen.In addition,the volatile by-products from the phosphor surface cause poisoning of the field emitter tips.Consequently,the FEDdevice ages at an accelerated rate.The low-voltage properties of ZnS:Zn,Pb were investigated for applications.Because of decomposition by irradiation of electron beam and generates of harmful gases such as SO2 for field emitter array,the surface coating and encapsulation of phosphors is an important technique to improve low-voltages cathodoluminescence and chemical stability and to reduce outgassing.SiO2 was used as the coating material because of its favorable band alignment when forming a heterojunction with ZnS.SiO2 exhibits minimal losses in electron penetration and has a penetration depth nearly twice as large as that of ZnS.At low excitation voltage,the surface of ZnS:Zn,Pb gets charged because of their higher resistivity.It is necessary to reduce the resistivity of the phosphor in order to improve its low voltage cathodoluminescent properties.To lower the resistivity of the ZnS:Zn,Pb,mixing the phosphor with In2O3 conductive powder have been reported.The low voltage cathodoluminescent properties of this phosphors mixed with and without In2O3 conductive powder are studied in this investigation.When mixed with In2O3,the critical voltage will decrease from 80 Vto 8 V.The CLemission intensity against voltage of ZnS:Zn,Pb is more efficient than ZnS:Ag,Cl and ZnS:Zn.The blue phosphor ZnS:Zn,Pb has an excellent luminescence properties and saturation properties under high current density.It is shown that ZnS:Zn,Pb can be used as FEDphosphor.关键词：ZnS:Zn;Pb;cathode-ray;anode voltage;anode current111|101|0更新时间：2020-08-11
- 摘要：The phosphor of BaSi2O5:Pb2+ has been widely used for manufacturing of black light lamps and treating many types of skin disease such as psoriasis,vitiligo,atopic dermatitis and so on.However,the detailed informations about the mechanism of flux BaF2 used for preparing BaSi2O5:Pb2+ phosphor can not be found in literature.The aim of this research is to work out the mechanism of flux BaF2 in the process of preparing BaSi2O5:Pb2+.BaSi2O5:Pb2+ sample was prepared by solid state reaction method at high temperature.Mixing compounds of barium and silicon which upon heating will react to form barium disilicate with a activating proportion Pb (NO3) 2.The firing temperature is approximately 1100℃.Crystal structure of BaSi2O5:Pb2+ phosphor is β-BaSi2O5.Ba2+ was substituted by Pb2+ partly in BaSi2O5 lattice so the XRDpattern of BaSi2O5:Pb2+ phosphor is identical with BaSi2O5 crystal.Effect of BaF2 concentration on ultraviolet intensity was studied.Mechanism that the addition of flux BaF2 promotes the solid reaction and enhances BaSi2O5:Pb2+ ultraviolet emission intensity was investigated by X-ray diffraction,heat-flux differential scanning calorimetry,and photoluminescence.Results indicate that BaSi2O5:Pb2+ phosphor forms at 800℃ by adding BaF2.High temperature firing with a small amount of BaF2 results in a phosphor with high emission intensity,BaSi2O5:Pb2+ emission intensity reach its maximum when the amounts of flux BaF2 is 8%.BaF2 and SiO2 combine to form SiF4 and BaSi2O5 then the formed SiF4 will react with BaCO3 to form BaSi2O5 again.The addition of flux BaF2 promote the solid state reaction,the temperature forming BaSi2O5:Pb2+ phosphor was reduced to 800℃ and it is consistent with thermodynamics theory.关键词：barium disilicate;flux;mechanism;thermodynamics102|132|1更新时间：2020-08-11
- 摘要：The electronic structures of the tetragonal and hexagonal Zn2SiO4 with super cells of 28 and 126 atoms were calculated by Vienna ab-initio Simulation Package with ultrasoft pseudopotentials.The calculated equilibrium lattice constants agree much well with the experimental values.Using the optimized equilibrium lattice constants,the densities of states and energy band structures were further calculated.The total densities of states of both structures show the valence and conduction bands.By analyzing the partial densities of states,the contributions of different electron states in different atoms are estimated.The d states of Zn and p states of Omostly contribute to the top of the valence band,and the s states of Zn make major effects on the bottom of conduction band.The similar densities of states in the mass of the two structures suggest that both structures have the similar electronic and optical properties.Moreover,the calculated energy band structures show that the tetragonal and hexagonal Zn2SiO4 have direct energy band gaps,which are promising semiconductors for short wavelength optoelectronic devices.关键词：Zn2SiO4;densities of states;energy band structures125|144|3更新时间：2020-08-11
- 摘要：ZnO is a good ultraviolet material that can be used widely in manufacturing photoelectronic devices.It has great value of researching and using.Porous alumina is a good kind of membranous substrate.Under the guidance of energy band theory,we tried to roll them into one.The bang gap could be changed under the influence and interaction of the porous alumina.Anew energy level was created in the band gap by increasing the concentration of zinc interstitial and oxygen vacancies.So a new photoelectronic material was produced successfully.Porous alumina were formed at different voltages in different acid solutions at 0℃.Then ZnO thin film was deposited on the porous alumina substrates in vacuum by Pulsed Laser Deposition (PLD).Several mea-surement techniques,including Scanning Electronic Microscopy (SEM),X-ray Diffraction (XRD) were used to analyze the morphology characteristics,crystalline phase and the composition of film.Its photoluminescence spectra were also measured.The experimental results showed that the morphology and photoluminescence of the film grown on porous alumina of different pore diameters differ greatly.The photoluminescence peaks of the ZnO film grown on porous alumina made from sulphuric acid aqueous solution are at 394 and 498 nm.The photoluminescence peaks of the ZnO film grown on porous alumina made from oxalic acid aqueous solution are at 417 and 466 nm.The photoluminescence peaks of the ZnO film grown on porous alumina made from phosphoric acid aqueous solution are at 415 nm and 495 nm.Because the film was fabricated in vacuum,it is rich in zinc and the photoluminescence spectrum changed when it was exposed in air for some time.Under the guidance of solid state energy band theory,we analyzed the photoluminescence spectra successfully.It can be discerned that we had produced a new photoelectronic material that has good properties.This gives us a new way in fabricating of ZnO .We deeply believe that this kind of material will be used widely in the near future.关键词：porous alumina;ZnO thin film;photoluminescence;grain size;quantum confinement effects117|120|4更新时间：2020-08-11
- 摘要：Afirst principles calculation is used to simulate the changes of the lattice constant,band gap,total energy and structure of MgZnO semiconductor alloys with the different MgO mole fractions.The calculated results show that the lattice constant diminishes and the crystal structure departures gradually from the wurtzite type as the MgO mole fraction increases.By comparison with the different positions of the Mg atom,it is suggested that the structure of MgxZn1-x Oalloy will change and the possibility of the phase transition will be higher than that of the phase separation as the MgO mole fraction increases.On the other hand,when the MgO mole fraction is increased,the band gap enlarges,which is mainly attributable to the shift of the top of the valence band away from the Fermi level.By construing the influence of all kinds of electronic states in Mg atom on the valence band,it shows that the contribution of Mg to the energy band near the top of the valence band takes turn from its p,d,s states.The density of the p states near the top of the valence band enhances prominently when the MgO mole fraction is increased.It indicates that the sp hybridization not only affects the structure of the crystal but also plays an important role for its electronic structures.关键词：MgZnO semiconductor;lattice structure;the first principle calculation121|113|1更新时间：2020-08-11
- 摘要：Zinc oxide (ZnO) nanowires were prepared on silicon substrate via a novel method of polymer complexation-sintering by using polar long-chain polymer (such as PAM and PVA) as self-assembling grid backbone. These ZnO nanowires were characterized by FE-SEM and HRTEMtechniques and their optical pro-perties were studied by photoluminescence spectroscopy and UVabsorption spectroscopy at room temperature. The mechanism of the ZnO nanowires growth and their photoluminescence, and the relation between process conditions and the mechanism are discussed.The ZnO nanowires, with diameter of about 50~80 nm and the lengths >4 μm, are hexagonal wurtzite single-crystalline and grown along the c-axis orientation preferentially. These nanowires have a strong UV emission band and a weak blue band as well as a strong UV light absorption. With decreasing the nanowires diameter, a blue shift of absorption peak appears.Polymer concentration and the complexing ratio of polymer to Zn2+ are the key factors controlling the self-assembling growth of ZnO nanowires. The mesh size and distribution of polymers, which are confined by the concentration of the polymer solution, control the diameter of the nanowires. Well vertically grown nanowires initiate only from the site that Zn2+ is complexed with the polymer, which forms the ideal nuclei, and the nuclei number is dependent on the complexing ratio of the polymer and Zn2+.The sintering temperature, sintering ambience and annealing condition affect photoluminescence of the ZnO nanowires. By controlling the sintering and thermal annealing conditions, the quality of the nanowires can be improved, and therefore, the better optical properties of the ZnO nanowires can be achieved. In high quality ZnO nanowires, a sharp strong emission peak at~393 nm appears due to the ultra-violet near band-edge emission of wide band gap ZnO , namely the free-exciton annihilation through an exciton-exciton collision process. The phenomena of UV band emission at room temperature might be attributed to the radial quantum confinement effect from ZnO nanowires. It can be concluded that the improvement of crystal quality, i.e., decrease of impurities and structure defects such as oxygen vacancies, stacking faults and dislocations, and the quantum confinement effect related to the nanostructures are responsible for the intensity increase of the observed UV emission at room temperature.关键词：ZnO nanowire;self-assembling;polymer soft-template;photoluminescence113|90|3更新时间：2020-08-11
- 摘要：Znic oxide is a Ⅱ-Ⅵ compound semiconductor with wurtzite structure.This film has many applications due to its large band gap,high exciton binding energy,positive optical and electrical properties. Thin films of zinc oxide have been prepared using various deposition methods, including RFsputtering,metal organic chemical deposition (MOCVD),pulsed laser deposition (PLD),molecular beam epitaxy (MBE),sol-gel,and so forth.ZnO thin films prepared by those methods usually exhibit (002) orientation with c-axis perpendicular to the substrate due to the lower surface free energy for (002) plane.The a-b axis preferred orientation is seldom reported because of it’s difficult to be formed.But as a novel preferred orientation,it maybe bring us new applications such as surface acoustic wave device (SAW).The single source chemical vapor deposition (SS CVD) technique is a useful method to form films, because it employs comparatively simple deposition equipment, and generate thin films at moderate temperatures and low vacuum ambient.We reported that ZnO thin film with a-b axis orientation was prepared by single source chemical vapor deposition (SS CVD) using Zn4 (OH) 2 (O2CCH3) 6·2H2Oas the precursor.The deposited ZnO layers on Si (100) semiconductor substrate were investigated with respect to the crystalline phase by X-ray diffraction (XRD), the micro-morphology by atom force microscope (AFM),and the stoichiometry by X-ray photoelectron spectroscopy (XPS). The results show that ZnO thin film with a-b axis was prepared under low substrate temperature of 350℃.The weak peak of ZnO (002) appeared while the substrate temperature enhanced to 450℃.The average grain size of ZnO is about 170 nm. ZnO films are stoichiometric with O/Zn atomic ratio (0.985) which very close to that of ZnO single crystal.关键词：ZnO thin film;SS CVD;a-b axis101|55|1更新时间：2020-08-11
- 摘要：ZnO is a wide band gap oxide semiconductor material with important and potential applications in sensor, transducer, surface acoustic wave devices, and optoelectronic devices, etc. In the past several years, various methods have been developed for synthesizing the ZnO nanowires. Among these methods, Vapor-liquid-solid (VLS) growth mode is widely used because it does not demand complex apparatus or sophisticated techniques and one can easily synthesized the ZnO nanowires by the catalyzing process of the metal liquid drop in the tip of the nanowires. In this work, based on the VLSgrowth mechanism, we successfully prepared the twin-crystal Sn catalysted ZnO nanowires with uniform shape and wurtzite structure by a simple method of thermal evaporation of a mixture of SnO powder and Zn powder under the pure N2 flow and O2 flow. The pu-rity, composition, microstructrue and crystallinity of the as-prepared ZnO twin-crystal nanowires were investigated by XRD, HRTEM, SEM and SAED. According to SEM images, we observed that the as-synthesized ZnO nanowires were straight and uniform, and were 100200 nm in diameter and several tens of micrometers in length, some even reaching millimeter level. TEM images and element analysis results verified that the spherical particle on the top of the nanowire was tin metal grain which played the role of catalyst in the process of nanowire growth. These suggested that the growth of ZnO twin-crystal nanowires was controlled by VLS mechanism. HRTEM images confirmed the twin-crystal structure of the nanowires. According to the SAEDimages, we made sure that the ZnO twin-crystal nanowires grew along [0110] direction and the twin-crystal plane was (1013). The relationship between the twin-crystal lattice was analyzed by the dark field images and the bright field images. We also explained the VLS growth mechanism of the nanowires.关键词：ZnO;twin-crystal;nanowires110|112|0更新时间：2020-08-11
- 摘要：Zinc oxide with high stability and a direct band gap of 3.37eV has attracted tremendous attention in recent years because of its high potential for application as short wavelength optical devices. Several techniques such as pulsed laser deposition, reactive thermal evaporation, sol-gel have been employed to synthesize high quality ZnO thin films. Sol-gel method was adopted to make ZnO thin films on n-Si (100) and they could be investigated from three parts. The X-ray diffraction spectra indicates that the structure of the ZnO thin films is polycrystal wurtzite structure with c axis preferred orientation. The annealing time and the annealing tempe-rature has great effect on the structure and particle size of the films, the proximate annealing temperature is around 500℃ by comprehensive experiments. The surface and profile character of the ZnO thin films can be observed by the Scanning Electrical Microscopy, which indicates that the growth of the films is uniform, the polycrystalline dimensions were determined to be in the range of 70~160 nm, consistent with the X-ray diffraction results. The optical properties of ZnO nanowires were investigated by room-temperature photoluminescence spectroscopy using a Xe lamp with an excitation wavelength of 230 nm. The photoluminescence of the ZnO sol indicates that as the aging time went on, the ultraviolet peak position moved to the short wavelength, from 342 to 340, 339 nm. The photoluminescence spectrum of the ZnO thin films at room temperature indicates that the ultraviolet peak positions were at 365, 390 nm, and the intensities of the emission were stronger, while the visible emission at 435 nm didn’t change obviously. The stronger peak positions at 460 and 690 nm are twice and three times frequency multiplication of the excitation light. The visible emission showed a weaker deep-level green emission than UV emission without being completely restrained. The PLspectra showed a strong peak around 390 nm at room temperature, corresponding to the ZnO free exciton emission.关键词：Sol-Gel;ZnO thin films;annealed;photoluminescence114|64|1更新时间：2020-08-11
- 摘要：ZnO is a wide and direct band semiconductor. It has a large fundamental band gap of 3.37 eV,which makes it a promising material for use in ultraviolet light-emitting and laser diodes. Moreover, ZnO possesses a large exciton binding energy (60 meV), which is much larger than that of GaN (25 meV) as well as the thermal excitation energy at room temperature, and can ensure an efficient exciton emission at room temperature. ZnO thin film can be fabricated by various methods such as pulse laser deposition, chemical or physical vapor deposition and molecular beam epitaxy.But pulse laser deposition has many advantage.ZnO thin films were prepared using a pulsed laser deposition (PLD) technique on Si (001) substrates.All samples were grown at the same substrate temperature and different oxygen partial pressure.After growing the samples, the influence of ambient oxygen pressure, ranging from 10 to 100 Pa, on the structural and optical properties of ZnO films was investigated systematically by XRD,SEMand PL.X-ray diffraction patterns indicate all films have (002) preferred orientation.But the experiment results indicated that as the oxygen pressure increases from 10 Pa to 100 Pa during the thin film deposition,the FWHMof (002) diffraction peaks becomg larger from 0.19° to 0.43°.We suppose this is because that at higher O2 pressure the kinetics of Zn and Oatoms are degraded by collisions with the ambient gas. These atoms have no sufficient energy to move to the plan of (002), so the crystallinity of the samples degrades.But the photoluminescence intensity of ultra-violet (UV) luminescence increases as the oxygen pressure increases.This is probably because the stoichiometry of oxygen-deficient ZnO film is improved by increasing oxygen pressure. At high oxygen pressure atmosphere, ZnO films bnough oxygen to absorb,so the stoichiometry of oxygen-deficient ZnO film is improved. Comparing XRDresults,it is concluded that the UV luminescence intensity strongly depended on the stoichiometry in the ZnO film rather than the micro-structural quality of the crystal.SEM resultes indicate that ambient oxygen pressure has an effect on the morphology of the samples.关键词：ZnO;PLD;stoichiometry;photoluminescence;FWHM142|73|2更新时间：2020-08-11
- 摘要：ZnO thin films with strong (002) preferred orientation have been deposited on Si(100) substrates using two-step AP-CVD. In the two-step growth process, a ZnO buffer layer was firstly grown at 450℃ for 5 min, and then a top layer was grown at 350℃ for 20 min. Arelatively high temperature buffer layer of ZnO provided a stable crystalline template for subsequent low temperature top layer to grow upon. In lattice-mismatched growth, ZnO thin film has a tensile built-in strain. The tensile strain in ZnO can be relaxed by providing sufficient thermal energy and meanwhile this relaxation process can give rise to more defects. Strong UV emission located at 381 nm is observed when excited with 325 nm light. The concentration of oxygen vacancies in the thin films increased after annealing at 800℃, and the 450~600 nm green emission band is observed. PLspectra for ZnO thin films grown by one-step method show typical UV emission located at 389 nm as well as blue emission centered at 437 nm. Likewise, the band of green emission is observed in PLspectra of thin films annealed at 800℃. The intensity of UV emission was dramatically decreased after annealing, which could be due to the increase of the size of ZnO particles and defect concentration. For the ZnO thin film grown by two-step method, the intensity of green luminescence after annealing in oxygen became weaker than that after annealing in air, so the corresponding mechanism for green emission is attributed to VO. For the ZnO thin film grown by one-step method, the intensity of green luminescence after annealed at oxygen became stronger than that after annealing in air. The relaxation process of tensile strain preferred to give rise to more OZn defects. Therefore, the corresponding mechanism for green emission is attributed to OZn. I-V properties also indicated that the emission mechanism of OZn was reasonable.关键词：two-step AP-CVD;ZnO thin films;photoluminescence;emission mechanism105|85|1更新时间：2020-08-11
- 摘要：The InxGa1-xAs material is very important for uncooled infrared detector and has spectral response from 1 μm to 3 μm. In recent years, there are growing needs for high In composition InxGa1-xAs detectors, the most important applications are spectral imaging including earth observation, remote sensing and environmental monitoring, etc. The InxGa1-xAs (x>0.53) was grown on semi-insulating (100) Fe-doped InP substrates by LP-MOCVD. The growth was performed using TMIn, TMGa, and AsH3 as growth precursors in a horizontal reactor. Two step method of In0.82Ga0.18As growth that the buffer layer was grown at low temperature of 450℃ and the epilayer was grown at higher temperature of 530℃ was studied. After depositing 300 nm InxGa1-xAs buffer layer, In0.82Ga0.18As epilayer with thickness of 1 μm was deposited. It was observed that the different In composition of InxGa1-xAs buffer layer influence on crystalline quality and surface morphology of In0.82Ga0.18As epilayer. The crystalline quality of the epilayer materials was characterized by X-ray diffraction (XRD). In our experiment, the In composition of the InxGa1-xAs buffer layers was 0.28, 0.53, 0.82 and 0.88, respectively. The full-width-at-half-maximum (FWHM) of diffraction peak for the buffer layer of In0.82Ga0.18As is 0.362° and is the narrowest among the four samples. The surface morphology was observed by scanning electron microscopy (SEM). The SEM image of the sample with buffer layer of In0.82Ga0.18As is a flat surface and is better than other samples with cross-hatches, pits or some defects. We found that the In composition of the InxGa1-xAs buffer can influence on the surface morphology of the In0.82Ga0.18As epilayer. The experiments show the crystalline quality and the surface morphology of the In0.82Ga0.18As epilayer is optimum when the In composition of buffer layer is the same as that of the epilayer.关键词：In0.82Ga0.18As;MOCVD;XRD;SEM106|65|0更新时间：2020-08-11
- 摘要：High power diode lasers have been used in printing, defense, medical, and materials processing because of their compact size, low cost per Watt, and high electricity-optics converting efficiency. InGaAs/InGaAs Pstrained-compensated single-quantum well structure with an emission-wavelength of 808 nm was grown.The back HRcoating was Al2O3/5 (HfO2/SiO2)/HfO2 and the front AR coating was Al2O3. Anovel water-cooler and heat-sink with new structure developed by ourselves performed efficiently. Driving by the SM-15 continuous laser power produced by δ Company of German, the CW module performed excellently and their lifetimes are up to 11732 hours under the room temperature. As a result, this reached the leading level domestically. The highest electricity-optics converting efficiency is up to 41.3%.The CW output power of the module reached to 46.2 Wat a current of 50 A.The slope efficiency is 1.15 W/Aand the central emission wavelength is 810 nm with a FWHM of 3 nm.808 nm high power semiconductor lasers are ideal light pump source for Nd:YAGlaser. Development of high-power semiconductor laser arrays will broaden the application of the semiconductor lasers in industry, medical treatment and display.关键词：high power semiconductor laser array;quantum well;HR coating;AR coating;array module141|54|1更新时间：2020-08-11
- 摘要：Zn1-xMnxSe belongs to a class of materials called diluted magnetic semiconductors (DMS) where their cations in a non-magnetic compound were partially replaced by magnetic ions. Within the rapidly evolving field of semiconductor spintronics researchers try to make the spin injection come true.Several approaches for spin injection have been realized, one of them is from a diluted magnetic semiconductor to a ferromagnetic semiconductor layer in an external magnetic field. It is important to prepare the polarized layer and to study their properties, since Zn1-xMnxSe as a polarized layer is popular with many researchers. In recent years, the material growth technique of Zn1-xMnxSe has been improved greatly. However, fewer researches related to Zn1-xMnxSe epilayers grown by metal-organic chemical vapor deposition (MOCVD) are reported than those grown by molecular beam epitaxy (MBE), although is more suitable for large scale production. Zn1-xMnxSe thin films with different Mn compositions are grown by metal-organic chemical vapor deposition (MOCVD) on GaAs substrate. We use Tricarbonyl (methylcyclopentadienyl) manganese (TCMn) as Mn source,use dime-thylzinc (DMZn) and hydrogen selenide (H2Se) as Zn source and Se source, respectively. The growth temperature is 480℃.The growth pressure is 104 Pa. The thickness of the samples are 150 nm measured by scanning electron microscope (SEM).Good crystallinity of sample is evidenced by X-ray diffraction and rocking curve measurements. Magneto-optical properties of Zn0.88Mn0.12Se thin films are investigated in magnetic fields up to 8 T. Two emission peaks near the band edge were observed. At the same time, a relative change of the emission intensity between two peaks is shown, we attribute the two peaks to the free exciton emission and Mn induced bound state excitonic emission respectively. Meanwhile, the band gap shows a red shift with increasing magnetic field due to the large sp-d change interaction关键词：Zn1-xMnxSe;metal organic vapor deposition(MOCVD);photoluminescence(PL);magneto-optical(MO)properties113|60|0更新时间：2020-08-11
- 摘要：DT-Eu3+ and DT-Eu3+·OTSnanoparticles (NPs) are prepared by reprecipitation under sonication. The two kinds of fluorescent NPs are both of small size, ~10 nm in diameter. But aggregation and greatly weakened luminescence of the pure chelate NPs disable them as fluorescent probes. With the introduction of appropriate hydrophobic silane, for example with 1:5 ratio of DT-Eu3+ chelate to OTS, the hybrid chelate NPs have intensive luminescence, uniform size and are well dispersed. Such improvements originate from the outside silica layer, which is developed from the rapid hydrolysis of alkoxysilane under basic environment (pH=9). The hydrated silica layer eliminates the hydrophobic interaction then aggregation, and isolates DT-Eu3+ chelate from water molecules.Formation details of Eu3+ chelate NPs via reprecipitation are revealed by the time-dependent absorption and luminescence behaviors of fresh-prepared suspensions. Evenly distributed microjets are assumed as precursors of NPs, which evolve from a loose structure to a compact one with the diffusion of THF. With the exhaustion of THF, NPs are resulted.关键词：lanthanide chelate;fluorescent nanoparticles;reprecipitation method;surface modification109|94|1更新时间：2020-08-11
- 摘要：It is well known that aromatic acids serve as excellent ligands to effect sensitization of lanthanide fluorescence. 1,3,5-H3BTC has three carboxylate groups and displays widely varying coordination manner, functioning as a monodentate, bidentate, bridging or chelating ligand in complexes with metal ions. On the other hand, the rare earth carboxylate complexes are the active area of research due to their fluorescence and application in high-teach industry, the application foreground is very fast. In recent years, there are many studies carrying on the carboxylate complexes in order to look for the good fluorescent materials, one of the major activities in these studies is the enhancement of fluorescence by using of certain rare earth ions,such as La3+,Y3+and Gd3+. The published dates on these were mainly focused on benzoic acid and benzene dicar-boxylate acid complexes, the complexes of trimesic acid with europium and lanthanum were comparatively scare. Only europium-trimesic acid fluorescence complexes were studied.Aseries of mixed rare earth complexes LaxEu1-x(BTC)·nH2O ( H3BTC=1, 3, 5-H3BTC, x=0, 0.1, 0.3, 0.5, 0.7, 0.9) have been synthesized by the reaction of trivalent rare earth chlorides with trimesic acid. The contents of rare earth, Cand Hwere measured by using EDTAtitration method and a Vario ELelemental analyzer, the constitution of these complexes was confirmed respectively as follows: LaxEu1-x(BTC)·nH2O (x=0, 0.1, 0.3, 0.5, 0.7, 0.9, n=0, 0.5,1.0).The IRspectra of free ligand and complexes were recorded by FTZR-8900 infrared spectroscopy with KBr pellet in the range of 350~3500 cm-1. There is obviously difference between the ligand and complexes. The results show that the similar structures of the complexes and the different coordination functions of the carboxylate groups. Fluorescence spectra were carrying out by using a Hitachi F-4500 fluorescence spectrophotometer. The results indicate that the complex can emit intense characteristic fluorescence from europium ion, the emission peak centered at 578~582 nm (5D0→7F0),585~600 nm (5D0→7F1),605~630 nm (5D0→7F2),645~660 nm (5D0→7F3),685~700 nm (5D0→7F4), the intensity of the fluorescence of the series complexes were greater in5D0→7F1 and5D0→7F2, and both the positions show splitting emission peaks. These results show that the coordinating pattern of the carboxylate groups were different. In addition, the fluorescence intensities of europium ions were sensitized by the doping elements lanthanum ions, and the intensity of fluorescence is the best when La3+:Eu3+=0.3:0.7, but the position of the emission peak does not changed. In conclusion, a series of mixed rare earth complexes LaxEu1-x(BTC)·nH2O (x=0, 0.1, 0.3, 0.5, 0.7, 0.9) have been synthesized by hydrothermal treatment. They can emit strong fluorescence.关键词：rare earths;europium-lanthanum complexes;trimesic acid;fluorescence;doping139|147|3更新时间：2020-08-11
- 摘要：Alow-high voltage level shifter, which is appropriate to field emission display (FED) driver IC, including its design and functions analysis is proposed. This circuit can operate safely under the conditions of 100 Vsupply and 10 mAoutput current. The maximum frequency reaches 20 MHz. The rise time and fall time of output waveform are 14 and 25 ns respectively while its load capacitance is 50 pF. The compatibility of the high voltage technology with low voltage technology is also discussed. LDMOS (Lateral-double diffused MOS) structure is used for the level shifter’s high voltage devices, HVCMOS ( High voltage CMOS) process is compatible with the standard 0.8 μm CMOStechnology which can integrate high voltage devices and low voltage devices on one chip. This process effectively decrease the production cost and increase the packing density of panel driving system.Moreover, the influences of thick gate oxide process for the High Voltage PMOSdevices during the fabricating processes on threshold of low voltage devices and high voltage NMOSFETare investigated.143|68|0更新时间：2020-08-11
- 摘要：Vitamin D2, also called ergocalciferol, has important effect on adjusting the in vivo metabolize of calcium and phosphorus. Vitamin D2 is manufactured by irradiation of ergosterol (E). Many studies have been done on the reaction, showing that UVirradiation of ergosterol produces many isomers: vitamin D2, pre-vitamin D2 (P), tachysterol, lumisterol and that the best irradiation wavelength is in the range of 270~310 nm for the conversion from ergosterol to pre-vitamin D2, which is not photochemically but thermally isomerized into vitamin D2. The purpose of this paper is to find a new light source with a better result for the photoreaction with a low cost. The tube glass of the lamp could absorb most of the spectrum range below 254 nm which gives more by-products, so there was not any filter solution used. Firstly a certain amount of ergosterol was dissolved in ethanol to make a reactant solution (1.0 mg/mL). This solution was put in the photochemical reaction apparatus and irradiated by low pressure Hg lamp. The reactant solution samples taken at different time were put in brown bottles, blown off ethanol with nitrogen gas. The dry sample was stored in refrigerator and was dissolved with n-heptane for liquid chromatography analysis. The intensity of the lamp was also measured at intervals. Through experiments, not only the relation between the transformation rates of photoreaction, but also the time of irradiation were studied. The decay curve of the light intensity within 300 h was also obtained. The result is that, the conversion ratio of the ergosterol was 65.5% in 65 min, and the selectivity of pre-vitamin D2 was 60.4%. The decay of the light intensity was only 13% in 300 h. Not any filter solution was needed in the photochemical reaction, this could decrease the whole cost in factory. And most important thing is that this lamp is very cheap, which shows a quite satisfying potential prospect for the industrialisation of vitamin D2.关键词：vitamin D2;ultraviolet lamp;photoreaction;selectivity115|73|0更新时间：2020-08-11
- 摘要：Hexagonal MgxZn1-x Oalloy layers with 0≤x<0.3 have been grown by plasma-assisted molecular beam epitaxy on sapphire (006) substrates. Their crystal structures are characterized by X-ray diffraction spectroscopy. The resonant Raman spectra were measured using 325 nm line from He-Cd laser by backscatte-ring geometry. The long wavelength frequencies of ZnO-like optical phonons measured in the resonant Raman spectra can be expressed as linear functions of x:ω(LO)=(580+147x)cm-1.ZnO/Mg0.12Zn0.88 Osingle quantum well (SQW) with 1.5 nm ZnO well width was grown on sapphire substrate. In the PLspectra at 5 K, Pband located at 3.371 eV was observed. At excitation densities higher than 76 kW/cm2, the Pband shows a typical super linear increase characteristic. With increasing the excitation density further, the Pband converges gradually at the saturation value of 3.354 eV with significant narrowing. It was attributed to the gradually enhanced exciton-exciton scattering. The integrated emission intensity versus excitation density follows the relation of Iex3.13. This superlinear increase indicates the typical properties of a super-radiation recombination.关键词：MgZnO alloys;Raman spectra;quantum well;super-radiation106|75|3更新时间：2020-08-11
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