最新刊期
卷 26 ， 期 3 ， 2005
- 摘要：The most of the experimental measurable quantities in many-body electron system, such as the optical absorption, luminescent spectra and exciton effect, are related to the excitation states description. The density functional theory with local density approximation (DFT-LDA) as a ground state theory, i.e. the solutions based on the Kohn-Sham equation is a powerful tool for studying the ground state properties in many-particle systems. However, the first principles computation of excited states is more complexity than ground-state calculations. A key problem is that the exchange-correlation interaction in excited states is differ from the ground-states. In recent years, nevertheless, several electronic-excitation theories have been developed. The most important theoretical and computational method include the many-body perturbation theory which is based on the quasi-particle concept and the Green function equation, the time-dependent DFT and the Bethe-Salpeter equation for describing the electron-hole interaction. Among them the central ingredient is an electron’s self-energy operator Σ that describes the exchange correlation effect beyond Hartree approximation. The implementations of the above theories are unavoidable to introduce some of approximations. A good approximation for Σ is the GW approach by Hedin. It is shown from computation simulations for many real condensed matter systems that the GW approach is a successful method for electronic-excitation problems. Another effective method for excited-states is so-called screen-exchange local-density approximation (sX-LDA). It is a combination of LDA and Hartree-Fock (HF)theory, in which the intrinsic local screen-exchange interaction has been replaced by a non-local one and a generalized Kohn-Sham equation (GKS) is given. Based on a PWscf package, the sX-LDA-PWscf method has been tested and indicates that an available approach for treating band-gap problem in semiconductors. In this paper, the many-body theories for the excitation process, its development and signification are reviewed. The relation and differences consist in different theoretical methods are discussed. On the based of above discussions, the applications of many-body theory to the band-band transition (band-gap underestimation problem) and exciton effect in semiconductors are presented.关键词：many-body theory;excited-state process;the first principles method115|162|2更新时间：2020-08-11
- 摘要：Compared with their corresponding bulk phases,nanoscale rare earth luminescent materials have come forth a lot of new luminescent phenomena such as the red shift of CTS, the broadening of emission peaks, the increase of quenching concentration, the changes of fluorescent lifetimes and quantum efficiency. Investigating and understanding these materials is not only of academic interest but also of technological importance for advanced phosphor applications. Therefore, in this article, progress on the study of nanoscale rare earth luminescent materials has been reviewed. Firstly, summing up the luminescent characteristic of nanoscale rare earth luminescent particles different from those of bulk materials; secondly, summarizing the preparation and spectrum properties of 1D nanoscale rare earth luminescence materials; thirdly, introducing the patterning of luminescent thin films and assemblies in the mesopore template of 2D nanoscale rare earth luminescence materials; finally, the future development trend for the nanoscale luminescent materials is forecasted. That is to say, in preparation, both nanoscale rare earth luminescent materials with good crystal shape, high brightness, nonaggregating, and narrow particle size distributing and ordered array luminescent devices composed of nanowires, nanotubes, nanorods and so on need to be developed. In fundamental studies, more efforts need to be done on the spectra properties rooted in their surface and interface effects. In applications, the key problems of low luminescent brightness and low stabilities must be resolved.关键词：rare earth;luminescence;nanomaterials;Eu3+;Tb3+173|193|18更新时间：2020-08-11
- 摘要：The effect is very prominence for the properties of magnetopolaron in an ionic crystal or polar semiconductor to character of an ionic crystal or polar semiconductor.With development of material science and experiment technology, magnetopolaron in an ionic crystal or polar semiconductor have been attention abroad. Many investigators studied the properties of the magnetopolaron by means of various theoretical methods and experimental methods. Wu et al. studied properties of two-dimensional polaron in magnetic field with Feynman path integral methods. Lassning investigated the theory of resonant polarons in narrow gap semiconductors by using variational method. Wei et al. studied properties of an interface polaron in a magnetic field of arbitrary strength by using Green function method. Nadkour discussed effect of magnetic field on surface polaron states in doped semiconductor. Brancus and Stan investigated energy levels of an anisotropic three-dimensional polaron in a magnetic field with Winger-Brillouin theory. Wollf studied bound magnetic polarons in dilute magnetic semiconductors. Stankiewicz et al. studied magnetization of bound magnetic polaron in Ga doped Cd1-xMnx Te.Tokuda et al. investigated the surface polaron and phase diagram and phase-transtion-like behaviour in the problems of different types of polaron by using improved Huybrechts method. Chen et al. discussed the properties of bound magnetopolaron by using linear combination operator.The effective mass properties of bound polaron in a magnetic field is studied by using improved linear combination operator and unitary transformation methods. The relation of vibration frequency and the effective mass of both weak-and strong-coupling bound magnetopolaron to the magnetic field and Coulomb potential are discussed. Numerical calculation for RbCl crystal, as an example, were performed and the results illustrate that the vibration frequency and the effective mass of strong-coupling magnetopolaron will increase with increasing magnetic field and Coulomb potential. The variety trend of vibration frequency of weak-coupling magnetopolaron to magnetic field and Coulomb potential has the similarity character. But the effective mass of weak-coupling magnetopolaron has no relation with magnetic field and Coulomb potential only increase with increasing coupling coefficient when coupling coefficient is limited in certain range.关键词：bound magnetopolaron;vibration frequency;effective mass116|79|1更新时间：2020-08-11
- 摘要：The problem of hydrogen-like systems has been extensively studied. Neutral donor and negative donor ion on the heterointerface in magnetic fields are investigated in this paper. The influence of magnetic and potential well has been calculated together. With the increasing of magnetic field, we find that the effect of magnetic fields makes the eigenenergy of D0 increases more and more. The binding energy increases follo-wing the strength of magnetic fields also. But the increasing rate of the binding energy decreases along the growth of fields. For D- center, at zero field, there is only a singlet bound state but no bound triplet state exists. The action of the magnetic fields makes the triplet state of D- change from unbound state to bound state. It is very important for the studying of the energy about hydrogen-like systems like D- center. We choose two different wave functions for different magnetic fields. Analytic results are obtained for the applicable range of two different wave functions. Using a variational method, we have calculated the ground energies and the binding energies of D0 center and D- center for the spin-triplet state of L=-1 in this structure. The optimum of four parameters about the orbit of D- center and two parameters of D- center were presented. We found that with the growth of the magnetic fields, the inner and outer orbits are compressed,the inner orbit of D- is alike to the orbit of D0.The extend parameters of the outer orbit are similar to the value of cyclotron radius. At zero field, the longitudinal parameter of the outer orbit extend to infinite. According to calculation, we get the corresponding threshold value of the magnetic fields at which the triplet state transforms from unbound state into bound state.关键词：D- center;spin-triplet state;binding-energy111|70|0更新时间：2020-08-11
- 摘要：With the development of several experimental techniques, for example, molecular beam epitaxy, metal-organic chemical-vapour deposition and electron beam lithography combined with reverse mesa etching, there has been a lot of work devoted to the understanding of hydrogenic-impurity states in low-dimensional semiconductor heterostructures such as quantum wells, quantum wires and quantum dots. In recent years, there has been great interest in investigating quantum dots both theoretically and experimentally. Due to the small structures of QD’s, some physical properties such as optical and electron transport characteristic are quite different from those of the bulk materials. The study of the impurity states in these low dimensional structures is an important aspect to which many theoretical and experimental works based.In recent years, the physical characteristic of a bound polaron in a quantum dot has been of considerable interest. Wang et al. investigated influence of the LO phonon on the ground state energy of the hydrogen-like impurity in a spherical semiconductor quantum dot by using variational method. 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 dot and wires within the frame-work of Feynman variational path-integral theory are derived by Chen et al. Melnikov et al. studied the effect of the electron-phonon interaction on an electron bound of an impurity in a spherical quantum dot embedded in a nonpolar matrix theoretically. The all-coupling variational method is used to calculate the polaron energy shift including interaction with both bulk and surface LO phonons.Bound polarons are discrete, confined electronic states, spatially localizd due to a local potential V(r), but sharing a common phonon state of the surrounding crystal. Woggon and Miller studied the energy states of polarons bound in a potential and determine the local optical absorption spectrum using first-order time-dependent perturbation theory with respect to the electron-phonon interaction. However, few of investigators studied the bound polaron in the quantum dot with the improving linear combination operator method so far.In the present paper, by using the improving linear combination operator and unitary transformation method, properties of the bound polaron in a parabolic quantum dot are studied for the weak electron-LO-phonon coupling case. Results show that the interaction energy of the weak-coupling bound polaron will decreases with increasing the Coulomb potential, the effective confinement length of quantum dot and the electron-LO-phonon coupling strength increasing. The vibration frequency of the weak-coupling bound polaron will decrease with increasing the effective confinement length,but will increase with increasing the Coulomb potential and the electron-LO phonon coupling strength. Meanwhile, the interaction energy and the vibration frequency will increase sharply with decreasing the effective confinement length. Those attribute to interesting quantum size effects.关键词：parabolic quantum dot;effective confinement length;Coulomb potential104|78|0更新时间：2020-08-11
- 摘要：To detect wind field in the upper atmosphere passive methods was used with imaging interferometer technique the main source is O(Ⅰ,Ⅱ) forbidden aurora. For stronger forbidden transition line, two necessary conditions of theoretical calculation are metastable and enough small electron density. O (Ⅰ, Ⅱ) satisfies the conditions and its forbidden lines are indicated. Then the corresponding photochemical reaction of O (Ⅰ, Ⅱ) forbidden aurora was investigated. The conclusion is that 10 forbidden (allowed) lines (557.7 nm, 630.0/636.4/639.3 nm, 672.8 nm, 732.2/733.2 nm,777.7/777.6/777.4 nm) can be used to detect upper atmospheric wind field, 5 lines (639.3 nm, 672.8 nm, 777.7/777.6/777.4 nm) increased comparing to WINDII, the visible wavelengths aurora is enlarged for imaging interferometer.关键词：selection rule;forbidden transition;aurora;metastable;photochemical reaction142|83|0更新时间：2020-08-11
- 摘要：The direct bandgap semiconductor compound ZnS and CdS were used as multiple based material. The luminescent characteristic were changed by multibase. (Zn,Cd)S:Cu,Cl electroluminescent material specimens were prepared by adding 5%, 7%, 10%, 15%, 20% CdS in ZnS respectively.There were two obvious thermoluminescence peaks from -180℃ to -20℃ in the thermoluminescence curves of the five specimens. The concentration of CdS did not influence the category and the depth of the traps in the material, the temperature of peaks are -150℃ and -50℃. The concentration of CdS did not change the relative intensity of the thermoluminescence peak at -150℃ obviously, the relative intensity were 55.6,46.7,60.2,65.0 and 66.5 respectively, but changed the relative intensity of the thermoluminescence peak a t-50℃.The relative intensity increased with the concentration of CdS increased. When the Cd2+ concentration was 5%, the peak of the curve was 7.1, when the Cd2+ concentration was 7%, the peak of the curve was 13.4. When the Cd2+ concentration was 10%, the peak of the curve was 32.4. When the Cd2+ concentration was 15%, the peak of the curve increased to 82.2 quickly and when the Cd2+ concentration was 20%, the peak of the curve forther increased to 97.6. The luminescence spectra of specimens moved from shortwave to longwave and the brightness descended as the concentration of CdS increased as shown by the measuring results of luminescence spectra and brightness. We therefore analyzed the result that excessive Cd2+ caused the decline of luminance because the replacement of Zn2+ by Cd2+ in the crystal lattice introduced the defects, and sequently the defects caused the formation of radiationless center. The energy of trapped electrons by the radiationless recombination center turns into the radiationless transition, the α phase which is disadvantageous to luminescence increases when the Cd2+ replaces the Zn2+ in the crystal lattice synchronously. The Cd2+ replaces the Zn2+ in the crystal lattice which results in the descending of the bottom of the conduction band, therefore decreases the forbidden band width of based material, which makes the luminescence spectrum moves from shortwave to longwave continuously.The thermoluminescence curves, luminescence spectrum and brightness changed accordingly as the concentration of CdS changed, which makes us find a way to obtain the (Zn,Cd)S:Cu,Cl powder electroluminescent material with the specific luminescence characteristic.关键词：electroluminescence;thermoluminescence;luminescence spectrum;brightness131|116|4更新时间：2020-08-11
- 摘要：We have successfully synthesized high-quality CdSe/ZnS and Au/CdSe/ZnS quantum dots(QDs) by simple chemical colloid methods. We try to explore the possibility of PL intensity enhancement of CdSe QDs in presence of Au nanoparticles (NPs). Due to the existence of surface plasma excitation of core Au, we have observed a great enhanced PL intensity in the core-shell NPs of Au/CdSe/ZnS as compared to CdSe/ZnS NPs. Here, the optimal fraction of Au NPs incorporation into CdSe/ZnS NPs was found to be 0.1 mol% Au NPs, which shows the highest PL intensity. We also fabricated a high efficiency organic electroluminescent device (OLED) using CdSe/ZnS and Au/CdSe/ZnS with phosphorescent Ir-complex as light-emitting materials. The quantum efficiencies of OLEDs were enhanced about 2 times as compared to blank device.关键词：chemical colloid methods;core-shell type CdSe quantum dots;electroluminescent device;phosphorescent Ir-complex147|97|5更新时间：2020-08-11
- 摘要：Organic light emitting devices (OLED) has gained a rapid development recently. It is technically crucial in the field of plate panel displays in the future. The most important superiority of OLED is that it can realize flexible displays-flexible organic light emitting devices(FOLED). White light, which is composed of three discrete peaks in R/G/B regions, is very important and particularly useful for full-color display. However, most of white OLEDs, so far, are fabricated with multilayer structures, which results in the complication of fabrication process and decline of quantum efficiency. So these devices are not suitable for the purpose of large-scale industrial manufacture.Bis-2-(2-hydroxyphenyl)benzothiazolate zinc (Zn(BTZ)2) is one of the best organic electroluminescent materials used for white light-emitting devices (OLED). PET slice with ITO is used as substrate of FOLED. We use Zn(BTZ)2 as main light-emitting material and fabricate a new type of flexible organic white-light-emitting devices. The configurations of the devices are as follows:PET/ITO/PVK:TPD/Zn(BTZ)2/Al. The bright and steady light emitting has been obtained, and the brightness of the devices comes to 1000 cd/m2 (at a driving voltage of 25 V). We also measure the CIE coordinates of the above devices, which are (x=0.242, y=0.359), and corresponding quantum efficiency value is 0.30%. Then the Rubrene is doped in Zn(BTZ)2, and the configurations of this devices are as follows:PET/ITO/PVK:TPD/Zn(BTZ)2/Al and ITO/PVK:TPD/Zn(BTZ)2:Rubrene/Al. The brightness of the devices comes to 1200 cd/m2 (at a driving voltage of 25 V), and the CIE coordinates of the above devices are (x=0.339, y=0.339), and corresponding quantum efficiency value is 0.35%. Details on the white-light-emitting characteristics of the devices are explained by the diagram of current density-voltage, optical current-voltage and quantum efficiency-current density, which are measured using Keithley 485 Picoammeter and 2400 SourceMeter. Last, we also discuss the emitting mechanism of the material and the devices.关键词：flexible substrate;white OLED;Zn(BTZ)2;doping116|130|0更新时间：2020-08-11
- 摘要：We have designed a device of new multi-layer structure and carried out the experiment on white light-emitting. In a white organic EL device with multi-layer, generally, white light emission can be obtained by blending blue emission and one or two others with long wavelength such as yellow, red or green emission. Because the energy band of material emitting blue light is broad and the efficiency of it is lower, how to raise the efficiency of blue emission from the white light-emitting device is the key of fabrication of a white organic light-emitting device with pure color, high efficiency and brightness. Therefore, we have designed the new structure of a device reasonably and increased the efficiency of blue light emission effectively and conveniently. The new multi-layer structure of the device limits blue emission within a very narrow scope between hole and electron transport layer, and causes one part of majority holes injected in to be captured by rubrene to combine with electrons in the transport process for yellow emission, and the other part of them to arrive the thin layer of DPVBi for increasing blue emission, so raising the efficiency of white light emission over blending yellow and blue emission, and enhancing the whole function of the device. From the electroluminescence spectrum, it is found that only the DPVBi and rubrene could emit light but NPB and Alq3 couldn’t. This explains that all energy of Alq3 is transported to DPVBi and rubrene. The structure of the device is ITO/NPB(35 nm)/DPVBi(4 nm)/Rubrene(0.1 nm)/Alq3(6 nm)/NPB(5 nm)/DPVBi(4 nm)/Rubrene(0.1 nm)/Alq3(6 nm)/NPB(5 nm)/DPVBi(4 nm)/Alq3(35 nm)/LiF(0.5 nm)/Al(200 nm). The commission international De L’Eclariage (CIE) coordination of the devices is very stable at (0.33, 0.34) while the applied voltage varies from 8 V to 14 V. The maximum electroluminescence efficiency is 4.0 cd/A at 10 V. It may be deduced that the reason why the device can emit white light is that blue and yellow emission can be given of by DPVBi and rubrene respectively. There are so characteristics because of the design new multi-structure making the efficiency of blue emission increased and the property of the device improved obviously. So we consider that the improvement of emission comes from doping of rubrene leading to carrier transporting from Alq3 to DPVBi.关键词：organic light-emitting diodes;white organic light-emitting devices;multilayer structure126|95|5更新时间：2020-08-11
- 摘要：Blue OLED is very crucial to realize full-color displays. It was harder to gain highly efficiency blue OLEDs compared with red and green OLEDs. LiBq4 was supposed to be a newly potential blue organic light-emitting material. As the states of the interface between organic layer and electrode and the film quality of organic layer affect the properties of OLEDs, we investigated the surface and interface states of LiBq4/ITO by using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). LiBq4 was deposited on ITO coated glass by routine vacuum evaporation. The thickness of LiBq4 was about 200 nm. The surface morphology of LiBq4 was checked by AFM within a area of 8.0 μm×8.0 μm both in lateral and topographic force contact modes. XPS was introduced to study the surface and interface electronic states of LiBq4/ITO. The scan spectrum was analyzed and the peaks of elements were deconvoluted to further investigate the chemical states of LiBq4.AFM results show that the surface of LiBq4 on ITO was very rough with many cracks and pores, indicating poor film quality of LiBq4 on ITO. From the analysis of the XPS spectrum, we found that, the concentration of contaminated C atoms was very high in the surface of LiBq4/ITO, which reduced significantly in the interface. This was another proof of the existence of cracks and pores in LiBq4, that these cracks and pores can lead to heavy absorption of gas molecules; LiBq4 was partially oxidized showed by the emergency of an oxidizing characterized shoulder peak in the C1s spectrum; The relative concentration of B atoms reduced in the interface, which indicate that some B atoms detached from LiBq4 and lead to the further oxidization of LiBq4; from the spectrum of N1s, we found that unlike the case in Alq3, no evidence shows B atoms bonding to N atoms through coordination, which leads to blue shift of the EL spectrum of LiBq4. But in the interface, a new shoulder peak emerged which may be caused by N atoms bonding with In and Sn atoms came from ITO layer. It may affects the EL spectrum of LiBq4 based OLEDs. From the B1s spectrum, we can also see that B atoms were in high valence, which agreement with LiBq4 molecular structure.关键词：LiBq4/ITO;surface;interface;atomic force microscopy (AFM);X-ray photoelectron spectroscopy(XPS)122|80|0更新时间：2020-08-11
- 摘要：Many organic complexes of rare earth(Sm,Eu,Tb,Dy) have a fine luminescent properties. Because the homochromatism theirs fluorescence is good, the intensity of luminescent and their interior quantum efficiency are higher, that is benefit to the panchromatic display. In recent year it caused denseness interest in high-tech industry and the application foreground is very vast. For looking for the good photoluminescence and electroluminescence materials, in our work three ternary complexes of Tb were synthesized with o,m,p-methoxybenzoic acid (o-MOBA, m-MOBA, p-MOBA) as the first ligand and 1,10-phenanthroline(phen) as the second ligand.The content of Tb,C,H and N were measured by using EDTA titration method and a Flash-EA model 1112 elemental analyzer. The constitution of the three complexes was confirmed respectively as follows:(Tb(o-MOBA)3phen·H2O, Tb(m-MOBA)3phen·H2O and Tb(p-MOBA)3phen.The IR spectra of free ligands and complexes were recorded by model 1730 Fourier transform infrared spectroscopy with KBr pellet in the range of 3503 500 cm-1. The results show that two characteristic absorption peak(υC=O,δO—H) of methoxybenzoic acid disappeared and the anti-symmetric and symmetric (stretching) vibration absorption peak of carboxyl(υas,υs) appeared in the complexes. These reveals that (methoxybenzoate) took part in the coordination. The characteristic absorption peak of phen(υC=N,δC—H) shifted to lower frequencies at different degree in the title complexes, which shows two nitrogen atoms in the phen also took part in the coordination.Excitation and luminescence spectra of the title complex were carried out and recorded by using a Hitachi F-4500 fluorescence spectrophotometer. Excitation spectra of the title complexes were obtained in a rang e of 200450 nm. Fluorescence spectra was observed in a range of 400-700 nm. The fluorescence spectra data shows four characteristic emission peak centered at 489, 545, 582 and 621 nm, which originated from the (5D4→7FJ(J=6-3) transition of Tb3+ ion respectively. The intensity of the transition fluorescence centered at 545 nm is the highest. The intensity of the transition fluorescence of the three complexes at 489 and 545 nm decreases according to the order o,m,p-methoxybenzoic acid. In a conclusion, three complexes of the terbium, Tb(o-MOBA)3phen·H2O, Tb(m-MOBA)3phen·H2O and Tb(p-MOBA)3phen were synthesized in C2H5OH solution. They result in strong emission with green color, among them the luminescent intensity of Tb(o-MOBA)3phen·H2O is the highest.124|60|2更新时间：2020-08-11
- 摘要：The Schiff bases of N, N′-bis(salicylidene)-1,4-diaminobenzene (L1), 4-[2-(hydroxy-1-naphthalen-1-ylmethylene)-amnio]-benzoic acid (L2) and 4-(benzylidene-amino)-benzoic acid (L3) are synthesized and characterized by 1H NMR, IR, UV, and elemental analysis. The results of fluorescent spectra indicate that the Schiff bases of L1, L2, and L3 possess strong luminescent properties. The excitation spectra of the Schiff bases have many fine characteristic excitation peaks and the maximal excitation wavelengths are 468 nm. The fluorescent lifetime experiments indicate that the lifetimes of the Schiff bases of L1, L2, and L3 are 199, 199, and 214 ns, respectively. The sequence of the fluorescent intensity of the fine powder Schiff bases is listed as L1>L2>L3, but the sequence of the ethanol solutions of Schiff bases is just reverse. The quantum yields of the ethanol solutions of L3, L2 and L1 are 0.60, 0.56 and 0.0086. The luminescent intensities of nanosized supramolecular materials that the guests of Schiff bases are encapsulated in the non-poplar channels of (CH3)3Si-MCM-41 are stronger than that of the composites encapsulated in the polar channels of MCM-41. The results show that the lipophilic channels of host are more favourable to fluorescence of the guest Schiff base molecule than the hydrophilic channels. Comparing with the excitation and emission peaks of the guest Schiff bases, the emission peaks of nanosized supramolecular materials shift generally blue. The excitation wavelengths of (CH3)3Si-MCM-41-L1, (CH3)3Si-MCM-41-L2, MCM-41-L2 and MCM-41-L3 are 529, 507, 507 and 505 nm (red shift), respectively. The excitation wavelengths of MCM-41-L1 and (CH3)3Si-MCM-41-L3 are the same as that of the guest Schiff bases. The lifetimes of (CH3)3Si-MCM supramolecular systems with L1, L2 and L3 as guest has obvious change, but that of MCM-41 supramolecular systems with L1, L2 and L3 as the guest keep almost unchanged, comparing with the guests of the schiff bases molecules. The experimental results of fluorescent lifetime show that the selectivity between the host and the guest exists obviously.关键词：Schiff base;mesoporous molecular sieve;nanosized supramolecular material;fluorescent lifetime;fluorescent quantum yield115|86|3更新时间：2020-08-11
- 摘要：Two dominant bands appear in the emission spectrum of Dy3+. The yellow band (575 nm) comes from to the transition 4F9/2→6H13/2 and the blue band (475 nm) corresponds to the transition 4F9/2→6H15/2. According to our former results, two emission peaks were observed in Tm3+ doped yttrium phosphate-vanadate phosphors, the narrow one at 475 nm originates from the Tm3+ ion transition 1G4→3H6, and the weak broad-band around 430 nm belongs to VO43- group. As we know, at a suitable yellow-to-blue intensity ratio, phosphor will emit white light. So yttrium phosphate-vanadate co-doped with Dy3+ and Tm3+ may be used as potential two-band phosphors.On the contrary to conventional methods, aerosol synthesis technique has been employed successfully to prepared phosphor particles with good morphology and uniformity of low concentration dopant in recent years. By coprecipitation reaction, high quality YP1-xVxO4:Dy3+,Tm3+ phosphor was prepared. The phosphor was characterized by XRD, SEM, and photoluminescence under UV excitation. The XRD patterns disclosed that the obtained YP1-xVxO4:Dy3+,Tm3+ is a compound. The SEM image showed that the size of the phosphor particles is uniform and submicron. The fine particle white emitting phosphors has a strong emission peak around 480 nm which is attributed to the emission from 1G4 to 3H6 of Tm3+ and the(4F9/2→6H15/2) transition of Dy3+, another strong emission around 576 nm originating from the Dy3+ transition 4F9/2→6H13/2, and a weak emission peak around 660 nm attributing to Tm3+ transition 1G4→3H4. It is expected that YP1-xVxO4:Dy3+,Tm3+ would be a promising two-band phosphors for high pressure mercury lamps (HPML).关键词：YP1-xVxO4：Dy3+;Tm3+;HPML;phosphor;spectra110|89|8更新时间：2020-08-11
- 摘要：Neodymium-doped phosphate laser glasses are the laser glass materials which were developed relatively early,and used in the fields such as nuclear fusion, high power laser amplifier and optic fiber laser and so on in China. But we are in trouble all the time,because the high thermal expansion coefficient leads to bad thermal and chemical stabilities and low-heat mechanical intensities. The thermal stability is very important to laser glasses and it is emphasis point in my work. By changing the composition of glass such as adding Al2O3,the thermal expansion coefficient of the sample dramatically decreases,and the thermal expansion coefficient of the glasses in this work achieves α=38.75×10-7/℃. Transition temperature Tf and softening temperature Tg of the glasses are 684℃ and 605.5℃ respectively. Introducing of F2 in glasses and improving preparation technology not only can get rid of Pt and water molecular, but also decrease phonon energy of glasses, at the same time, improve phonon efficiency and optimize spectroscopic properties. Fluorescence and absorption spectra and thermal expansion coefficient of Nd3+-doped phosphate laser glasses are tested at room temperature. Spectroscopic parameters of Nd3+-doped phosphate laser glasses were calculated according to their absorption spectrum. The transitions of Nd3+from 4F3/2 to 4I11/2 and from 4F3/2 to 4I13/2 are corresponding to fluorescence wavelength 1056 and 1321 nm respectively under the excitation of 514 nm argon ions laser at room temperature. Generally, quantum efficiency of energy level transition are determined by the phonon energy of substrate to large extent. The more phonon energy,the stronger multi-phonon non-radiation relaxation, so the smaller quantum efficiency is corresponding to the weaker fluorescence intensity. To decrease phonon energy of glass substrate, introducing F2 in glasses can improve phonon efficiency and enlarge bandwidth of fluorescence spectral line. All the researches extend the application range of neodymium-doped phosphate laser glasses.关键词：phosphate glasses;neodymium ion;spectroscopic properties153|194|5更新时间：2020-08-11
- 摘要：The Y2O3:Eu3+ nanocrystals scatered in SiO2 hosts were synthesized by sol-gel method. According to XRD patterns, the samples calcined at 800℃ were noncrystals and the size was smaller. The calcining temperature was elevated to 1000℃, the crystalline phase began to occur and the nanocrystals were well crystallized at 1200℃ and the particle size did not become large. The spectrum principles of Y2O3:Eu3+ nanocrystals scattered in SiO2 for different annealed temperature and concentration have been intensively discussed. At ultraviolet laser excitation at room temperature, the emission intensity of samples increased with elevated annealing temperature for the same concentration. For the same annealing temperature, the intensity became strong as the increase of concentration. The intensity of 5D0→7F0 was stronger than of 5D0→7F2 and the origin was analysed. Appropriate doped concentration and calcining temperature were studied. The excitation spectra and site-selective excitation spectra for 5% Y2O3:Eu content (mass fraction) calcined at 1300℃ were measured. The average size was 50 nm. According to selective excitation spectra of 5D0→7F1 and 5D0→7F2, Eu3+ occupied four sites.关键词：sol-gel;luminescent intensity;Eu3+115|111|1更新时间：2020-08-11
- 摘要：To develop the Ce3+ and Tb3+ co-activated LaPO4 nanowires (NWs) green phosphors, a significant question should be considered: In one-dimensional NWs, how do the electronic transition and the energy transfer processes between Ce3+ and Tb3+ change in comparison with the bulk crystals? To our knowledge, there is no report on this topic until now. In practice, the studies on energy transfer processes between different rare earth centers in NWs are quite rare, too. Recently, we successfully fabricated Ce3+-activated, Tb3+-activated and Ce3+/Tb3+ co-activated LaPO4 NWs as well as micrometer rods (MRs) by the hydrothermal method. Their fluorescent spectra and dynamics were studied in contrast to the MRs. The results indicate that the structure of both the samples belongs to monoclinic phase. The intensity of Ce3+ or Tb3+ in MRs for singly doped samples increased a little in contrast to NWs. It is important that the intensity of Tb3+ in NWs corresponding to Ce3+ excitation increased 3-5 times than that in MRs. The extinction concentration of Ce3+ and Tb3+ in NWs increased than that in MRs. The electronic transition rate of Ce3+ and Tb3+ in NWs had only a little variation in comparison with that in MRs, and the energy transfer rate and efficiency of Ce3+→Tb3+ in NWs reduced. Surprisingly, the brightness for the 5D4→7F5 green emissions of Tb3+ via energy transfer of Ce3+→Tb3+ in NWs increased several times than that in MRs. To reveal the origins of above phenomenon, the 5D3 level decay of Tb3+ was measured. The results indicated that the decay curve included two proponents: a fast and a slow process. The slow proponent was dominant in NWs and fast proponent was dominant in MRs. We suggested that the slow proponent corresponded to the transition of 5D3→5D4 and fast proponent corres-ponded to the relaxation from 5D3 to other defect centers. The increased intensity of Tb3+ in NWs via energy transfer excitation was attributed to the decreased energy loss in the excited states being higher than 5D4 due to the hindrance of the boundary.关键词：LaPO4：Ce3+/Tb3+;nanowires;energy transfer125|157|3更新时间：2020-08-11
- 摘要：YAGG:Tb phosphor is very excellent in its brightness, especially in the projection TV it shows good application foreground.The particle size of phosphor has compact relation with definition of image,the smaller the particle size is, the higher the definition is. Nano phosphor can improve the definition and give us more clear picture. The preparation of YAGG:Tb nano phosphor is introduced, the way of preparation is urea-sol method,it has some merits than other methods.This method is inorganic way,we can acquire nano phosphor.The particle-size and shapes of different temperature superfine-particle phosphors are observed and taken photos with scanning electron microscopy (SEM).The diffraction patterns of them are measured by X-ray diffractometer (XRD).In the end,we discuss the experiment result.The experiment of urea-sol method for synthesizing global,well-proportioned,super fine-particle YAGG:Tb green phosphor whose particle-diameter is 80~300 nm is discussed in detail. The particle-size and shapes of superfine-particle phosphors prepared at different temperature are observed in the photos taken by scanning electron microscopy.We found that the particle is bigger at the higher temperature and the phenomenon of conglomerating appears.The way of surface coating is adopted to solve the conglomerating problem. The diffraction patterns of them are measured by X-ray diffractometer (XRD) and the microcrystalline-structure is analyzed. We may draw a conclusion the that particle we prepared is YAGG:Tb. A comparison in luminance is given between superfine-particle phosphor and Japanese commercial projection-tube phosphor. So the characteristics of luminance should deeply and carefully promoted in many aspects.关键词：nanometer;phosphor;urea-sol method;YAGG：Tb141|162|0更新时间：2020-08-11
- 摘要：Silicon nitride has better high temperature capabilities than most metals combining retention of high strength and creep resistance with oxidation resistance. In addition, its low thermal expansion coefficient gives good thermal shock resistance compared with most ceramic materials. Silicon nitride is widely used in semiconductor process and micro-electromechanical systems (MEMS) for its advanced material properties. The silicon nitride thin films prepared by low pressure chemical vapor deposition (LPVCD) technique at the deposition temperature of 950℃ shows strong greenish-blue visible photoluminescence (PL) emission with five separate peaks at 2.7, 2.69, 2.4, 2.3 and 2.1 eV, respectively, by the 3.45 eV laser excitation, at room temperature. The results of TEM, IR and X-ray photoelectron spectroscopy(XPS) show that the N/Si ratio of the films is 0.75,which means the film is silicon-rich, and the film is constructed with mosaic crystal silicon nanoclusters embedded in silicon nitride solid, the dimension of which is about tens nanometer. To find out the luminescence property of as-deposited thin films, a series of LPCVD SiNx films was treated by rapid thermal annealing (RTA) for 15 s in N2 at 1000,1100 and 1200℃, and we analyzed the changes in PL spectra, composition and microstructure caused by the RTA process. We found after RTA, the relative intensity of some peaks changed, and two new photoluminescence peaks appears at 3.0 eV and 2.8 eV.We believe the peaks at 2.7,2.3,2.1 eV is separately caused by the electronic transition of ≡Si0→N—Si—O, ≡Si0→N-, Ec→≡Si-, the peaks at 2.69 and 2.4 eV is caused by the electronic transition of ≡Si0→Si—O—Si, Ec→≡Si0.Those peaks will change after RTA, for the thin film’s composition and defect state density can be changed by RTA process. And we also found the nano-silicon microstructure can greatly decreased the stress of SiNx film (to 107 Pa), which can help us to prepare high quality silicon nitride films.关键词：nano-silicon microstructure SiNx film;photoluminescence;membrane stress;rapid thermal annealing(RTA)110|167|2更新时间：2020-08-11
- 摘要：The structure characteristics of ZnO thin films epitaxially deposited on two-inch (00.1) sapphire substrate by atmospheric metalorganic chemical vapor deposition (AP-MOCVD) were determined by X-ray double-crystal diffractometry methods. The strained lattice parameters, misorientation, bending radius and stress of ZnO films were estimated. The strained ZnO lattice parameters and misorientation between ZnO film and substrate were attained from a pair of symmetric and asymmetric diffraction,which contain the diffraction peaks of ZnO epilayer and sapphire substrate.The experimental bending radius was determined from the differences of the X-ray rocking curve peak positions move of the different points on ZnO film and experimental stress was calculated from that radius. Theoretical bending radius and residual thermal stress were also calculated,which is caused by the difference in the thermal expansion coefficients between the ZnO layer and sapphire substrate. The result shows that misorientation and lattice distortion were induced in ZnO layer by the actions of thermal and lattice stress. The misorientation azimuth angle is nearly the same with the miscut azimuth of sapphire substrate, which indicates that substrate miscut is one of the key factors of the misorientation,but the misoriention angle is greatly little camparing with the substrate miscut angle. Comparing to the direct-growing film, the sample with a low-temperature buffer layer has less misorientation angle and lattice stress. Meanwhile, the experimental bending radius of the sample with a low-temperature buffer layer is smaller than that of the direct-growing sample and residual thermal stress is relatively bigger. That means the low-temperature buffer layer is of great benefit to reduce the misoriention and lattice distortion of ZnO films on Al2O3 and enhance the quality of ZnO film.关键词：ZnO;DCXRD;misorientation;bending radius122|140|1更新时间：2020-08-11
- 摘要：Si-B-C-N materials derived from polymer precursors recently received a high attention due to their outstanding high temperature stability. It has been reported that the precursor-derived Si-B-C-N materials do not degrade at temperatures up to 2000℃,even in nitrogen-free environments. In addition, they possess superior mechanical properties such as excellent creep and oxidation resistance. Therefore these materials are promising for components which were serve at temperatures above 1000℃,such as turbine parts.Much studies have focused on amorphous Si-B-C-N materials,while especially studies on crystal Si-B-C-N nano-materials are still under the way.We focus on the optical properties of Si-B-C-N nanomaterials derived from boron-modified polysilazanes precursors. Scanning electronic microscopy (SEM) and high transmission electronic microscopy (TEM) observation showed a special structure just like bamboo. Photoluminescense (PL) spectrum was measured under 488 nm laser excitation from 89 K to 290 K. Three emission peaks were observed at about 580, 620 and 740 nm,respectively. It is believed that the emission peaks were concerned with impurity level in the bandgap.关键词：polymer precursor;nano Si-B-C-N;emission;impurity level143|165|0更新时间：2020-08-11
- 摘要：Noble metal nanostructures have been the focus of study for many decades because of their use in real or potential applications. It has been demonstrated that the intrinsic properties of metal nanostructure are usual closely related to the shape, size, and structure. Many methods are used to prepare noble metal nano-particles with different kinds of shape such as nanospheres, nanorods,nanobelts, nanodisks, and nanoprism. Colloidal hollow gold has been studied extensively in recent years due to their interesting physical properties and promising applications. For example, the special absorption of hollow gold nanostructures in the NIR region makes these materials as ideal candidates for photothermally trigged drug releasing in tissues, which is quite useful in the biomedicine. Several groups are studying in this domain. An application of this technology to thermal ablative therapy for cancer was described. For these reasons, hollow nanostructure produced by a shape-controlled procedure has become a new and interesting research focus. The gold nanoshells were prepared by an easy wet-chemical synthesis method and Ag nanoparticles were used as the templates. TEM images indicated the shells were sphere in shape and the size was about 20 nm. The size was homogenous and no hard agglomerates. The absorption in the optical resonance shifted from visible (~400 nm) to near-infrared (NIR, ~800 nm) with the increase of the dosage of HAuCl4. The temperature grads (ΔT) of the gold nanoshell hydrosol under the exposure of an 808 nm optical-fiber laser were measured. The highest ΔT was 5.5℃ (1.9 W, irradiation area was 1 mm2). The gold nanoshell hydrosol is promising to be used in biomedicine such as photothermal cancer therapy and photothermally triggered drug release for its special photothermal convert property, as the cancer tissues will be killed at 42℃.关键词：Au;nanoshell;photothermal conversion167|176|2更新时间：2020-08-11
- 摘要：The realization of ohimic contact to n-GaN is usually achieved by using Ti/Al bilayer electrodes with high temperature annealing. Nevertheless, the process of high temperature annealing may destruct the electronic structure of devices, such as quantum well and superlattice structure. The ultimate objective of this research work is to obtain low resistance ohimic contact to n-GaN without high temperature annealing, thus avoiding the destruction of electronic structure effectively. In the research both nonalloyed condition and low temperature annealing are applied. Under nonalloyed condition, we firstly use alloyed TiAl3 as contact electrode material directly on n-GaN with carrier concentration of 2×1018 cm-3. Compared with conventional Ti/Al bilayer structure, alloyed TiAl3 structure facilitates the realization of nonalloyed n-type ohmic contact. However, with annealing at 500℃, the contact behavior of Ti/Al bilayer is improved rapidly and achieves ohmic, which is lower than the temperature assumed in some papers. After applying RIE process, both Ti/Al bilayer and TiAl3 alloyed electrodes behave ohmic, which indicates that the surface of GaN is cleaning, thus intimate contact of Ti and GaN is vital to achieve ohmic contact to n-GaN. In the further experiment, Ti/TiAl3 bilayer structure is introduced to compare with TiAl3 alloyed structure. Both of the two structures behave ohmic with RIE process, yet TiAl3 alloyed shows lower contact resistance, and excess Ti has no obvious effect to contact behavior under nonalloyed condition. After annealing with different temperature, Ti/TiAl3 bilayer structure tends to form an ohmic contact with lower contact resistance. It proves that excess Ti is activated to form ohmic contact at high temperature annealing. Further analysis implies both of the nitrogen vacancies and TiAl3 mechanisms play a critical role to form a low contact resistance ohmic contact to n-GaN, under the condition of nonalloyed or low annealing temperature. Accordingly, based on alloyed TiAl3 structure, Ti/TiAl3/Ni/Au structure is designed, which decreases the contact resistance significantly, and the specific contact resistance of 3×10-5 Ω·cm2 is obtained with CTLM measurement.The introduction of TiAl3 alloyed material can make a role as high temperature annealing in the aspect of forming TiAl3 at the interface. With a certain thickness ratio, Ti/TiAl3 can achieved low ohmic contact with low temperature annealing. Therefore, TiAl3 alloyed will be promising in the application field of photoelectron and micro-electron devices that require strict temperature conditions.关键词：ohmic contact;GaN;alloyed TiAl3;RIE;specific contact resistance117|135|0更新时间：2020-08-11
- 摘要：We report, for the first time, white light emissions of a single Sr2MgSiO5:Eu2+ material. The emission spectrum consists of two bands, located at 470 and 570 nm, respectively. The two bands have different fluorescence lifetimes, being attributed to Eu2+ ions substituted by different Sr sites. White light is generated by mixing the two colors. The excitation spectra of the two bands are both distributed within UV range. A white LED has been fabricated employing the white phosphor and a near UV of 400 nm InGaN chip. As the forward-bias current is 20 mA, the color temperature is 5664 K, the color coordinates(CIE) are x=0.33, y=0.34, the color rendering index(CRI) is 85% and the luminescent intensity is 8100 cd/m2. Experiments demonstrate that CIE and CRI of the white LED change slightly with the variation of forward-bias current, indicating that the phosphor presented in this work is a promising material for use in new generation white LED lighting.关键词：white LED;white phosphor;single white phosphors227|246|46更新时间：2020-08-11
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