最新刊期
卷 22 ， 期 3 ， 2001
- 摘要：InN epilayers have been grown on GaAs(001)substrates by MBE at 500℃ under the N2 pressure of 2.67×10-2Pa.During the growth,the In flux was varied from 3×1014 to 24×1014 atoms/cm2 sec.The InN films were characterized by X-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED) measurements.It is found that the cubic phase InN was grown at initial stage of growth, but the transition from cubic phase InN to hexagonal phase InN occurred with increase of the thickness of InN epilayer.The X-ray reciprocal space mapping (RSM) measurements show that the hexagonal phase InN whose c-axes are oriented in the GaAs<111>B direction is dominantly grown on (001) GaAs.关键词：RHEED;X-ray RSM;h-InN106|69|0更新时间：2020-08-11
- 摘要：The InGaN/GaN films were grown by metalorganic chemical vapor deposition (MOCVD) at atmospheric pressure. Properties of these films, such as their chemical component, thickness, the crystalline quality, and optical properties, were investigated by Rutherford backscattering / channeling measurement and photoluminescence measurement. The growth was carried on (0001) oriented sapphire substrates. TEGa, TMGa, TMIn, and blue ammonia (NH3) were used as Ga, In, N precursors, respectively. Before the growth, a thin buffer layer with thickness of about 15nm was deposited at 520℃ and crystallized at 1060℃ for 6 minutes. In the growth of this layer, the / ratio in gas phase was adjusted to achieve good quality of GaN films and prevent the cracks usually occurred. GaN films were grown at 1060℃. After growth, the temperature was decreased to 650～800℃ to growInxGa1-xN layers. Two InxGa1-xN samples were discussed in this paper. During the growth, the flow rates of NH3, TMIn, and TEGa were 1 l/min, 2 8μmol/min and 1 6μmol/min, respectively. The growth temperature was 760℃ and N2 was used as main carrier gas. Sample A used 70ml/min H2 as the carrier gas of metalorganic precursors, but sample B used 70ml/min N2. The In mole fraction and growth rate of InxGa1-xN films were largely influenced by the carrier gas in metalorganic precursors when the main carrier gas was N2. The In mole fraction in InxGa1-xN alloys was 0 10 in sample B. However, the x value was 0.06 in sample A. It means that H2 can largely influence the In mole fraction in InxGa1-xN films, even the flow rate of H2 was very small. This result is in agreement with other reports. The value of the growth rate was 10 6nm/min for sample A, and that was 6 0nm/min for sample B. This phenomena, the dependence of the InGaN growth rate on little precursors carrier gas H2 have never been reported to our knowledge. We considered that InN can reduce the lifetime of the reactive In atoms at the film surface during growth, which lead to the increasing of Ga atoms in the film surface. So, the growth rate of alloys increased.关键词：MOCVD;InGaN;Rutherford backscattering and ion channeling;photoluminescence87|66|0更新时间：2020-08-11
- 摘要：The technology of deep level transient spectroscopy (DLTS) develops from the technology of measuring transient capacitance. Through the temperature scanning, it can rapidly,exactly describe the deep levels of the sample. And it has wide measuring range. So it has been becoming the popular measurement to study the deep level of the semiconductor. Zinc oxide is a self activated crystal with hexagonal wurtzite structure and has a gap of 3.3eV at room temperature.ZnO phosphor powders have been studied for several decades. Recently, ZnO films have attracted attention due to their wide applications in photoelectric materials such as surface acoustic wave guide, piezoelectric materials, transparent electrodes for some solar cells, and as a buffer layer for GaN. As most efforts focus on short wavelength semiconductor materials, stimulated and spontaneous ultraviolet emissions of ZnO thin films have been found. Comparing to the semiconductors used in conventional lasers, the UV emission of ZnO films has shorter wavelength. If a practical emitting device with short wavelength made by ZnO films could be fabricated, it must have exciting applications in compact disk recorder and other photoelectronics areas. In order to know the mechanism of its photoluminescence, the research in the properties of ZnO films is therefore important. In this article, we use deep level transient spectroscopy (DLTS) to study the ZnO/p Si heterostructure which was treated by two different temperatures (850℃, 1 000℃) and to find its relationship to the photoluminescence .The results showed that the sample 1# (850℃ treated) has three obvious deep levels (E1,E2,E3) and the sample 2# (1000℃ treated) has only E1 level. But the density of this level is higher than that of sample 1#. At the same time, the photoluminescence spectra of the samples were also measured. It is found that the sample 2# has higher density of photoluminescence because it has less levels and higher density of the level. Through the higher temperature (1000℃) treatment, some defect levels which affect the photoluminescence disappeared, and the crystal lattice become more integrated. So the treatment temperature of 1000℃ is efficient to improve the density of the photoluminescence of ZnO.关键词：deep level transient spectrum (DLTS);photoluminescence (PL) spectrum;defect;and new donor101|72|2更新时间：2020-08-11
- 摘要：Nanocrystal ZnS:Mn phosphor has been prepared by sol method using inorganic materials at room temperature. The nanocrystal phosphor of ZnS:Mn has cubic crystal structure with average 3nm of particle size, emitting bright orange light at peak wavelength 608nm with the full width of half maximum 75nm under UV 365nm excitation, and the brightness as high as the corresponding bulk pure cubic ZnS:Mn phosphor. According to the results reported by R.N.Bhargava, in comparison with the bulk ZnS:Mn phosphor the nanocrystal ZnS:Mn has nearly high luminescent efficiency with its luminescent decay time at least 5 orders of magnitude faster. It means that the oscillator intensity of luminescent centers in nanocrystal ZnS:Mn enhances at least 5 orders of magnitude than that in corresponding bulk ZnS:Mn. The discovery of high luminescent efficiency nanocrystal phosphor ZnS:Mn aroused the great interest to lots of researchers in the world. But these results are difficult to explain according to the normal concept. So checking these results by experiment has very important meaning in theory and experiment. In this paper the main purpose is to make a luminescent decay comparison between the nanocrystal and normal bulk crystal (particle size in micrometer) ZnS:Mn phosphors. In this comparison we controlled two factors:(1) The nanometer and bulk ones need have same crystal structure. A commercial bulk ZnS:Mn phosphor usually has mixed structure of cubic and hexagonal crystal which mainly depends on the sintering temperature and the doping concentration of luminescent activator Mn2+. In our experiments, under two different sintering conditions we prepared the bulk phosphors in two pure structures, cubic and hexagonal, respectively. These bulk crystal ZnS:Mn phosphors have the average particle size in micrometer order of magnitude. (2) Luminescent decay will sensitively depend upon the excitation condition, such as excitation intensity and mode like photoluminescence (PL) and cathodeluminescence (CL). In general, high intensity excitation will cause faster decay and CL will also cause faster decay than PL for the same phosphors. So in our experiments, the photoluminescent decay comparison between nanocrystal and bulk crystal ZnS:Mn was made in the same excitation condition. Under the excitation of the fourfold frequency pulse laser of Nd:YAG at 266nm (pulse width:9ns, pulse repeat frequency:3～30Hz, single pulse energy in 1.064μm:750 mJ), we have carefully investigated the decay time of nanocrystal cubic ZnS:Mn phosphor in comparison with that of pure cubic and pure hexagonal microcrystal bulk ZnS:Mn phosphors. The 1/e luminescent decay times of these phosphors are as follows:(1) Pure cubic nanocrystal ZnS:Mn has two distinct exponential decays. The two decay time constants are 186 and 1 078μs and its amplitude ratio is 4:1; so the former is major one, which determines the 1/e decay time. (2) For pure cubic bulk crystal ZnS:Mn, there is only one exponential decay, the decay time constant is 944μs. (3) For pure hexagonal bulk ZnS:Mn, one exponential decay time constant is 1.2ms and a small amplitude hyperbolic component having extremely long decay time. These results show that the nanocrystal ZnS:Mn phosphor do have shorter photoluminescent decay time than the corresponding bulk crystal ZnS:Mn phosphors (no matter hexagonal or cubic one), but the shortened rate is only several times, not 5 orders of magnitude.关键词：nanocrystal phosphors;ZnS:Mn;photoluminescence;decay time89|82|4更新时间：2020-08-11
- 摘要：It has been reported recently that some Eu3+ doped nanocrystalline silicate and oxide were with higher quenching concentrations in comparison with the corresponding bulk materials. Computer simulation has shown that the size confinement and the existence of high density surface states affected significantly the quenching processes of the rare earth dopants in nanoparticles. To understand the feature of the energy transfer process in rare earth doped nanoparticles is important for further seeking applicable nano phosphors. This paper reported, the preparation of a series of Y2O2S:Tb3+ nanocrystals with uniform sizes and varied Tb3+ concentrations. The mean size of all the samples prepared was evaluated, based on the X-ray diffraction pattern, to be about 20nm. Emission spectra of Tb3+ in nanocrystalline Y2O2S with different Tb3+ concentrations were measured under 257nm excitation. With increasing Tb3+ concentration, the luminescence intensity of both the 5D4→7FJ and 5D3→7FJ transitions increases at first and then decreases. Emission intensities reach their maximum at the Tb3+ concentration of 0.6% for the 5D3 emission and of 6.4% for the 5D4 emission. The lifetime of the 5D3 level is 0.31ms in the sample with 0.065% Tb concentration, comparably shorter than 0.78ms in bulk Y2O2S:0.3%Tb. This fact indicates that the surface states do act as the quenching centers for the luminescence, and the increasing of quenching concentration comes probably from the lower quantum efficiency of the nanocrystals. The dependences of the intensity on Tb concentration and the decay curves of both 5D3 and 5D4 emissions fit with theory. The quenching of the 5D3 state is governed by dipole dipole interaction, while that of the 5D4 state by exchange interaction. Both the intensity and temporal analyses coincide and result in the same conclusion. Similar to bulk material, concentration quenching of the 5D3 state is due to cross relaxation. The mechanism of the concentration quenching of the 5D4 state is that the energy migrates among the Tb ions and is trapped finally by quenching centers, most likely, the surface states.关键词：energy transfer;Y2O2S:Tb3+ nanocrystal;concentration quenching104|63|9更新时间：2020-08-11
- 摘要：Nanosized mesoporous molecular sieve MCM-41 was synthesized with tetraethyl orthosilicate (TEOS) as the source of silica and cetyltrimethylammonium bromide (CTABR) as the template under supersonic wave conditions. By means of high-resolution transmission electron microscopy (HRTEM), the nanosized MCM-41 was observed which contains Φ10～40nm spherical balls possessed Φ2.7nm regular uniform channels. The nanostructured material (NSM) MCM-41 has good dispersibility and its particle diameter is well distributed. The luminescent functional supramolecule MCM-41-Eu(Phen)4 between the nanosized MCM-41 and Eu(Phen)4 was prepared in EtOH, and characterized by TEM, XRD, TG, IR and fluorescent spectroscopy. The NSM of MCM-41-Eu(Phen)4 are 10～40nm spherical balls too. The XRD patterns are similar to the normal crystal of MCM-41. The IR spectra showed that the guest Eu(Phen)4 is non infrared active and the OH absorptions of the host MCM-41 are specially fine, strong and sharp in the supramolecule system MCM-41-Eu(Phen)4. The luminescent spectra indicated that an energy barrier (0.395eV) exists in MCM-41-Eu(Phen)4 preventing infrared radiation (<3030cm-1) from reaching the guest Eu(Phen)4 due to shielding effect of the host on the guest. The experimental results also showed that the molecules of Eu(Phen)4 presenting in the channel of MCM-41 had formed the centers of luminescence, hence the functional supramolecular NSM with strong luminescence under UV excitation was obtained. The transitions 5D0 →7FJ (J=1,2,3,4,5) of Eu3+ with peak values 590.4nm, 614.6nm(617.9nm), 653.4nm, 685 4nm and 699 6nm have been observed in which the electric dipole transition, especially, 5D0→7F2 (617.9nm red), is as stronge as that for the fine powder of Eu(Phen)4. This work has resulted in a new field of luminescence and a new route to prepare complex luminescent NSM.关键词：functional NSM of supramolecule;MCM-41 meseporous molecular sieve;MCM-41-Eu(Phen)4;luminescence91|67|5更新时间：2020-08-11
- 摘要：In recent years, the borate luminescence materials have received much attention owing to their low synthetic temperature and high luminescent efficiency. In order to search for the new luminescent material, the synthesis and luminescence properties of Na3(La1-xSmx)2(BO3)3(x=0～0.10) were firstly reported in this paper. The samples in polycrystalline form were synthesized by the conventional solid state reaction. The mixture of Na2CO3,La2O3,Sm2O3 and H3BO3 with an excess of 5 mol% were preheating at 500℃ for 10 hours, then sintered 24 hours at 720～750℃for Na3(La1-xSmx)2(BO3)3(x=0.005～0.10), and 935℃ for Na3La2(BO3)3. In the course of experiment, the purity of all samples was checked by X-ray diffraction (XRD). The single phase powder of Na3(La1-xSmx)2(BO3)3 in range of 0.0～1.0mol% were obtained when repeated heat treatment caused no further changes in the X-ray powder diffraction patterns. X-ray diffraction analysis shows that all these compounds are isomorphous with Na3La2(BO3)3, which belongs to orthorhombic systems, space group Amm 2. This indicats that the La3+ ions(r=0.105nm) in Na3La2(BO3)3 can be partly replaced by the smaller rare earth ions Sm3+ (r=0.096nm) without change of crystal structure. The infrared spectra of the compounds Na3La2(BO3)3(a), Na3(La0.995Sm0.005)2(BO3)3(b) and Na3(La0.94Sm0.06)2(BO3)3(c) scanned between 400～2000cm-1 in the transmittance mode were measured. The results were in agreement with the characteristic values of the BO33- groups. The minor difference observed in the infrared spectra of (b) and (c) at 450～550 cm-1 might be due to the changes in the Sm and La ions and their ionic radii. The luminescent properties of Sm3+ in Na3La2(BO3)3 host were investigated by the excitation and emission spectra at room temperature. The emission spectrum obtained for Na3La2(BO3)3:Sm3+ under 400nm excitation at room temperature in range of 500～750nm was shown in Fig.2(a). There were four main emission peaks at near 564, 599, 645 and 707nm, among which the intensity of the 599nm line was the highest. These emission peaks were all narrow sharp peak not broad bands. They originated from the f f transitions of Sm3+ ions 4f electrons, which assigned to 4G5/2→4H5/2transition between 550～570nm, 4G5/2→6H7/2 transitions between 580～610nm, 4G5/2→6H9/2 transition between 630～655nm and 4G5/2→6H11/2 transitions between 700～710nm, respectively. They belonged to the characteristic emission of Sm3+ ions. The excitation spectrum for Sm3+ 599nm emission recorded at room temperature showed lines corresponding to transitions 6H5/2→(4K, 4L)17/2(345nm), 6H5/2→(4D, 6P)15/2(362nm), 6H5/2 →4L17/2 (375nm), 6H5/2→4K11/2(400nm), 6H5/2 →4M19/2(6P, 4P)5/2(418nm), and 6H5/2 →4I13/2(4I9/2)(475nm). As we can see in Fig.2(b). The intensity of the transition at 400nm was found to be the highest in all the spectra. It showed that the strongest fluorescence emission at 599nm could be obtained under 400nm excitation. At room temperature, the emission spectra of Na3(La1-xSmx)2(BO3)3 at different concentration were recorded by the excitation of 400nm. The relative peak heights can change with the concentration of Sm3+, while the peak positions remain practically unchanged. The relationship between fluorescent intensities of 599nm emission peak of Sm3+ and act ive rare earth ion concent rat ions in Na3(La1-xSmx)2(BO3)3 was described in Fig.4.It shows that Sm3+ luminescence exhibits the concentration quenching effect,which might be due to energyt ransfer resulted from higher concentrations and the cross relaxation process among mate levels pairs,for example 4G5/2→6F9/2 and 6F9/2→6H5/2 energy levels.So the suitable concentration of Sm3+luminescence in the Na3La2(BO3)3 host was about 6mol%.104|72|20更新时间：2020-08-11
- 摘要：Gd2O3:(Ce3+, Eu3+) is a potential luminescent material which can act both in fundamental research and application. In the past two years, Wegh et al. realized the quantum cutting grounded on the energy transfer between some rare earth ions such as Gd3+→Eu3+, Gd3+→Er3+ and so on, the quantum efficiency approximates to 200%. So we investigated the energy transfer in Gd3+ Ce3+ Eu3+ system, prepared for the design of the new type materials based on effective quantum cutting. Gd2O3:(Ce3+, Eu3+) micro crystals were prepared by the sol-gel method. The samples were checked to be pure cubic phase by X-ray powder diffraction, the mean size of particles is about 400nm. The excitation spectra of Ce3+ (λem=450nm) and Eu3+ (λem=619nm) in the UV range were researched, and the emission spectra of Ce3+ and Eu3+ were measured with UV excitation respectively. The results showed that the energy transfer between Gd3+ and Ce3+, Gd3+ and Eu3+, Ce3+ and Eu3+ correspond to the energy transfer from 8S7/2→6DJ and 8S7/2→6IJ (Gd3+) to 4f (2F7/2, 2F5/2)→5d (Ce3+), from 8S7/2→6DJ and 8S7/2→6IJ (Gd3+) to 7F 1,2,3,4 →5D0 (Eu3+), and from 5d→4f(2F7/2, 2F5/2) (Ce3+) to 7F 1,2,3,4 →5D0 (Eu3+),respectively. We also made use of synchrotron radiation light to detect the excitation spectra of Gd2O3:(Ce3+, Eu3+) in the UV VUV range, and the emission spectra with VUV (180nm) excitation. The emission spectra of Ce3+ (λem=450nm) was decomposed to four sub bands with UV excitation, while it was decomposed to two sub bands under VUV excitation. These results indicate that Ce3+ substituted for Gd3+ and located in two kinds of different sub lattices. Gd3+ can transfer energy to two kinds of different sub lattices effectively, while the host just can transfer energy to one kind of different sub lattices. The energy transfer from 8S7/2→6DJ and 8S7/2→6IJ (Gd3+) to 4f (2F7/2, 2F5/2)→5d (Ce3+), and from 5d→4f(2F7/2, 2F5/2) (Ce3+) to 7F 1,2,3,4 →5D0 (Eu3+) occurred simultaneously, so it is concluded that the cascade energy transfer Gd3+→Ce3+→Eu3+ exists in Gd2O3:(Ce3+, Eu3+) micro crystals.关键词：Gd2O3：(Ce3+;Eu3+);UV-VUV excitation spectra;luminescence;cascade energy transfer98|79|0更新时间：2020-08-11
- 摘要：The luminescence properties of PbWO 4 doped with Gd3+ have been studied. The PbWO 4:Gd3+ microcrystal powder was obtained by solid phase reaction method. The microcrystal with strong green emission band was prepared in air with rich oxygen at 875℃ for 10 hours, and the microcrystal with strong blue emission band was prepared in vacuum with active carbon at 800℃ for 8 hours. By measuring the emission of PbWO 4:Gd3+ for 311nm excited by 274nm, and measuring the excitation spectrum of PbWO 4:Gd3+ from 200～300nm of 311nm emission, it can be concluded that the luminescence of Gd3+ in PWO was quenched. So both the excited states 6I 7/2 and 6P 7/2 of Gd3+ are located in the conduction band of PWO. The luminescence from 4f 4f transition of Gd3+ is slow, its quenching should not increase the slow components of luminescence of PWO in general, so the luminescence of PWO:Gd is still that of PbWO 4 host dominated by fast components. As a structure sensitive material, PWO is sensitive to oxygen during preparing and annealing. The strong green component of luminescence from PWO:Gd powder compounded in air with rich oxygen is as about 100 times as that of crystal compounded in a atmosphere lack of oxygen, similar to that of crystal sample annealed in air. Its emission and excitation spectra are showed in Fig.1, and the concentration dependence of the peak emission intensity of PWO:Gd is showed in Fig.2. For PWO:Gd prepared in air, the intensity of the green emission of PWO is increased by doping with 50～100ppm Gd. But beyond 100 ppm, Gd doping will quench the luminescence of PWO. For PWO:Gd powder prepared in vacuum with active carbon, its emission is mainly in blue band and the blue emission intensity is increased remarkably as 3～4 times as that from PWO crystal grown by Bridgman method. As shown in Fig.3, the main wide excitation band peaked at 378nm is very different from that prepared and annealed by other method or in other atmosphere. It is a new phenomenon. The new excitation band at 378nm can not excite the green emission. It excites directly the blue centers. The luminescence of PWO doped with low concentration of Gd is stronger than that of pure PWO, and its concentration dependence of the blue band intensity is shown in Fig.4. For PWO:Gd emitting in blue band, prepared in vacuum with active carbon, doping with about 100ppm Gd would improve the luminescence of PWO best, and doping with over 300ppm Gd would make the quenching of PWO luminescence. Low concentration doping of Gd could improve the luminescence intensity of the green and the blue band of PWO. This is not caused by the compensation process of the structural defects of PWO. Because green band and blue band are produced by two different kinds of luminescence centers, these two kinds of luminescence centers could not be compensated by one kind of defects. Mechanism of the Gd3+ enhancing PWO is probably due to the inverse energy transfer in crystal, Gd3+→PWO host, as the excited states of Gd3+ are included in the conduction band of PWO host. The PWO doped with Gd is a good scintillating material.关键词：PbWO 4;Gd doping;scintillator;luminescent property93|73|0更新时间：2020-08-11
- 摘要：The localized electronic state is different from the free atomic state in condensed matter. The strong or weak interaction between localized electronic state and the crystal lattice results in a big or small shift of the atomic balance site in solid states. This phenomenon was called crystal lattice relaxation. Rare earth ions may have a partially filled 4fn (1≤n≤13) electron shell both in free and in bound states. The peculiarities of the physical properties of rare earth compounds are determined by the presence of this partially filled shell. Internal 4f electrons remain localized near their own nucleus and interact relatively weakly with the ligands. In this work, a serial of glasses with different ratios of H3BO3 and PbF2 in molar and with same density of purity was prepared, using the solid melt method. The excitation spectra of Eu3+ in these glasses were measured with the HITACHI F-4500 fluorescence spectroscopy, and the phonon sideband spectra were obtained from the excitation spectra. A detail script of the theory of electron phonon interaction in the condition of weakly coupling system, such as trivalent rare earth ions in the condensed matter, was confirmed. The experimental technique for obtaining phonon sideband spectra was concluded. Based on the theory, we proposed a method to obtain the Huang-Rhys factor from the phonon sideband spectra of Eu3+ in these serial glasses with different components. The Huang-Rhys factors for different glasses were calculated. The relationship between Huang-Rhys factor and sample components was obtained and discussed. Then we investigated the dependence of the constant α on the energy gap, between two levels, for different glasses with various Huang-Rhys factors. The available area of energy gap law, Anr,=Ce-αΔE was discussed. Lastly for instance, we ticked off some values of α and C in different crystals, obtained by researchers. A detail analysis of effect of α and C on the nonradiative transitions was confirmed.关键词：Huang-Rhys factor;nonradiative transitions;phonon sideband;Eu3+ ion105|165|5更新时间：2020-08-11
- 摘要：Ce3+:LiSrAlF6 crystal is a solid state laser material potentially capable of efficiently producing tunable ultraviolet (UV) output. Recent results suggest that it may be the most efficient continuously tunable, rare earth doped UV laser material reported to date. There are some defects in Ce3+:LiSrAlF6 crystal. These defects will affect the laser and luminescence properties of crystal. In this paper, the temperature dependence of luminescent intensity (I-T) of Ce3+:LiSrAlF6 crystal with X-ray excitation from 105K to 300K has been studied. The luminescent intensity is enhanced " specially " in the range of 237～300K, which is probably caused by traps. In order to verify our surmise, we investigated the thermoluminescence of Ce3+:LiSrAlF6 crystal from 105～300K with X-ray excitation at 105K for two minutes. From 237～300K, two peaks locate at 258K and 274K respectively. These two peaks are accord to two kinds of traps, whose depth are 0.51eV (258K) and 0.55eV (274K). Comparing I-T curve with TL curve, the enhanced part of I-T curve is coincided with temperature range in which TL peaks locate. Because the TL peaks originate from traps, we suggest that the special structure of I-T curve is caused by the traps effect. That is, during the period of measuring the I-T, at lower temperature, some charge carriers relax to luminescent center and luminesce, while some other charge carriers is captured by traps. The release probability of bonded carriers is described as C×exp(-E/kT), where C is a constant, E is the depth of trap and T is temperature. With the temperature rising, the bonded charge carriers will release from the traps at higher temperature, via conduct band then relax to luminescent center and give out light, which make the intensity of luminescence enhanced. The origination of defects of Ce3+:LiSrAlF6 crystal is discussed too. It is primary that Ce3+ occupies the sublattice of Sr2+ in Ce3+:LiSrAlF6 crystal, forming CeSr3+ defect. Generally, fluorine vacancies (VF) always exist in fluoride. Ce Sr3+ and VF are negative charge center, which form electron traps. The lithium vacancies (VLi) are principal positive charges, which compensate the negative charge Ce Sr3+ and VF, VLi form hole traps. In conclusion, the "special" structures of I-T curve in the range of 237～300K is explained by the traps effect, which is verified by means of TL. The depths of two traps are 0.51eV and 0.55eV respectively. These traps mainly originate from CeSr3+ and some intrinsic defects such as VF and VLi.关键词：Ce3+：LiSrAlF6 crystal;temperature dependence of luminescence;trap;thermoluminescence;UV laser109|96|0更新时间：2020-08-11
- 摘要：Eu3+ doped materials has made an important role in the PDP, but the color purity and fluorescent efficiency of the materials now available can not be satisfactory. To look for better materials, the fluorescent properties of Ln7O6(BO3)(PO4)2:Eu(Ln=La,Gd,Y) have been studied. The samples were synthesized by high temperature solid phase technique. The structures of the samples were complicated, it was showed by the infrared absorption spectra that the basic structure unit are [BO3]3- and [PO4]3-, but because there are interaction between of [BO3]3- and [PO4]3-, the radius of Eu3+ ions is different from the La3+, Gd3+, Y3+ ions, and there exists other anion group, etc., the absorption spectra of Ln7O6(BO3)(PO4)2:Eu are not entirely the same as that of LnBO3 and LnPO4 doped with Eu. The excitation spectra in the region of VUV UV and the emission spectra in the visible region were studied. The excitation spectra are consisted of the Eu3+-O2 charge transfer band and the host absorption band. The location of the Eu3+-O2 charge transfer band shifted to the high energy with the radius of the La3+, Gd3+, Y3+ decreasing; in the excitation spectra of the Gd7O6(BO3)(PO4)2:Eu and Y7O6(BO3)(PO4)2:Eu, the ratio between the absorption in the VUV region and in the Eu3+-O2 charge transfer band is higher than that in the La7O6(BO3)(PO4)2:Eu; there is high absorption at 147nm in the Y7O6(BO3)(PO4)2:Eu.关键词：VUV-UV excitation spectrum;Eu3+ ions;Ln7O6(BO3)(PO4)2;emission spectrum88|52|2更新时间：2020-08-11
- 摘要：In the early 1970s, Ibach carried out low energy electron diffraction (LEED) experiments on ZnO and other semiconductor surface. The surface polaron in the crystals are of considerable interest. The behaviour of the electron phonon interaction near the surface or interface of a crystal has been studied by many investigators by means of various theoretical methods.Most polar crystals are diatomic and cubic and their crystal structure belongs to NaCl,CsCl or ZnS type.In these crystals there is one mode of the longitudinal optical(LO) phonon.The properties of crystals have been studied by a great variety of techniques,in the case of crystals having only one LO phonon branch.However,a large number of polar crystals,with several atoms per unit cell,have more than one LO phonon branch.For example,in cuprite such as CuO2 there are two LO phonon modes and a large number of perovkites(SrTiO3,BaTiO3,LiNBO3...) also have more than two modes.Recently,there have been studied the polaron problem with many LO phonon branches.The properties of the surface polaron in polyatomic polar crystals are investigated using a linear combination operator and a simple unitary transformation by one of the authors.However,the influences of the electron interaction with both bulk longitudinal optical(LO) phonons and surface optical(SO) phonons on the effective potential of the surface polaron in polyatomic crystals has not been studied so far.The purpose of this paper is to explore the effect of the interaction between the electron with both LO and SO phonons on the effective potential of the surface polaron in polyatomic semi infinite crystals using a linear combination operator and a unitary transformation method.关键词：polyatomic semi infinite crystals;surface polaron;effective potential90|73|0更新时间：2020-08-11
- 摘要：Thd contribution of electrochemistry method to the research of the electroluminescence cell has been discussed in this paper. In the electroluminescence cell electrons coming from metal electrode (such as Al, Mg) inject into the lowest unoccupied orbital (LUMO) and radioactively recombine with holes to generate electroluminescence. The energy transport can be calculated by electro chemistry method in the theory. The energy of LUMO and HOMO is corresponded to the potential of cathodic current peak and anodic current peak in the voltammogram chart,respectively.But the experiment results indicated that it is difficult to calculate the band-gap energy accurately using electrochemistry method from I-V voltammogram chart,because the electrode process in teh interface between the electrode and the solution is so complicated that much polar potential,such as double electronic layer polarization,concentration polarization need to be considered.In fact the I-V voltammogram still give us many useful massages to explain the EL behaviors.The electrodic potentials in a redox reaction in dicate the attention ability for accepting or losing electrons in a electrochemistry reaction.A bigger I-V area in the voltammogram will show a bigger charge or discharge quantity as a electron accepter or a electron donor.It is easy to find out most of organic polymers possessing conjugated double bonds appear a reversible redox characteristics such as polythiophene and 3 methyl poly thiophene. Ultra violet spectrograph and voltammograms of organic luminescent material,Alq,BBOT and PBD have been investigated in this paper.Results of I-V cyclic voltammograms indicated Alq,BBOT and PBD apperas unreversible electrochemistry process with a big cathodic current peak,the cathodic reduction potential of PBD is more negative than that of Alq.Both of results of UV and voltammograms are in a good agreement with the electroluminescence behaviors.关键词：organic luminescent materials;electroluminescence;energy band match;voltammograms107|100|1更新时间：2020-08-11
- 摘要：Using 3-aminopropyltriethoxy-silane(KH550) and 3-glycidoxypropltrimethoxy-silane(KH560) as precursors, Disperse Orange 3 (DO3) was doped into above sol and ormocer in 3wt% concentration, and the sol-gel derived films with 4μm thickness coated on ITO film were fabricated. Corona poling was performed by applying a high voltage of + 5kV to a needle electrode. After corona poling of the film at 185° for 4 hours, about 1/5 of DO3 molecules remained in solid state film, estimating from their spectra, and the concentration of DO3 molecule in poled film was estimated about 1.6×1019cm-3. Second harmonic generation (SHG) was used to probe the size and stability of the orientational order of the poled films. The second harmonic intensity of the films was measured using p (parallel polarized) excitation and p detection, and compared with that generated by a y-cut quartz crystal. No Maker fringe pattern for the film was observed, we could assume that the coherence length was much larger than the film thickness. The SHG intensity increases with increasing angle and reaches to maximum at θ=52°. The effective second order nonlinear coefficient, deff and d33 were estimated about 0.11pm/V and 0.14pm/V, respectively, and the intensity of SHG decreased slightly and remained ～80% of the initial value even after poling 500 hours. It is thought that for a combination of DO3 and organic inorganic gel the pore shrinkage and high baking temperature stabilize the nonlinearity in particular. Furthermore, due to leading KH550 (containing-NH2 group) into sol-gel derived matrix, it is expected that the hydrogen bonds between DO3 and KH550 in matrix are formed and the more density of matrix is reached, which can keep the oriented DO3 stable.关键词：DO3;ormocer;corona poling;second order nonlinearity93|76|0更新时间：2020-08-11
- 摘要：A model of Single Molecule Photon Cryocooler(SMPC) was built in generally meaning. Quantum transitions in single molecule, which was excited by photons with different energy and treated as a cryocooler, were simulated with computer. Frequencies and number of phonons, which participate in thermal excitation in ground state and in excited states and during fluorescence emitting, were studied. The conclusion that single molecule in ground state has more cooling power was obtained. So in optical absorption and emission process, the thermo dynamic effect in ground state is different from that in excited state for fluorescent cooling of single molecule. So, when we choose cooling material for anti Stokes fluorescent cooling usage, splits of the energy level in ground state of luminescence center is more important than in excited state.101|121|0更新时间：2020-08-11
- 摘要：By replacing the AlxGa1-xAs with [GaAs/AlAs] superlattice, a novel semiconductor/superlattice distributed Bragg reflector has been grown by molecular beam epitaxy system, at the same time the optical and electrical characteristics have also been measured. From the experimental results the center wavelength of the DBR reflection spectrum is about 850nm, the 19-period-DBR has the reflectivity as high as 99.5%, and the reflection bandwidth is as wide as 90nm. Moreover, using twice self-designed tungsten filament mask and proton implantation method we made the 15×15μm2 square current flowing area to measure the series resistance of the p type DBR. This method avoided the difficulty in controlling the depth of implantation, and prevented the occurrence of side etching in wet chemical etching. The series resistance of the p type DBR is just about 50 Ohms. Therefore this kind of DBR has both a high reflectivity and low series resistance. Comparing with the normal semiconductor/semiconductor DBR, this kind of DBR can also simplify the structure design and fabrication of DBRs by omitting the modified heterointerface structures in the former DBR. It is clear that the simplification of the structure of DBRs can be a serious advantage in the VCSELs structure, therefore these factors reveal that this kind of DBR may have sufficient quality for the characteristics of VCSELs or the fabrication of the devices. Finally, the dependence of the series resistance of the DBR on temperature is also experimentally studied, from the result the series resistance depends on temperature slightly. It is clear that the thermal current depends more on temperature than the tunneling current, so the tunneling current should account for the majority of the current flowing in this kind of DBR, and it makes the DBR depend on temperature slightly. In VCSELs, the temperature characteristic is an important point in the performances of devices, so the characteristic of resistance depending on temperature slightly in this kind of DBR may improve the temperature characteristics of VCSELs with this kinds of DBRs.关键词：distributed Bragg reflector(DBR);superlattice;molecular beam expitaxy(MBE);reflection spectrum;series resistance103|82|1更新时间：2020-08-11
- 摘要：Alkali halide crystals containing color centers (CCs) are well known as laser active media in optically pumped tunable solid state lasers generally operating at liquid nitrogen temperature. Among them, lithium fluoride has several unique characteristics because it can hold laser active defects stable at room temperature (RT) and emit in the visible and near infrared. Despite the deep knowledge on alkali halide crystals, little attention was devoted to non epitaxial alkali halide films. In the last years we devoted our attention to the growth and characterization of LiF films in order to study the spectroscopic properties of CCs created by low energy electron beams for application in integrated active devices. Polycrystalline LiF thin films of total thickness t between 0.5 and 3.8μm were grown by thermal evaporation on amorphous substrates, mantained at fixed temperature Ts between 30 and 350℃ during deposition. Their structural, morphological and optical properties are strongly dependent on the evaporation parameters, especially on Ts. Low energy electron beam irradiation gives rise to the efficient formation of stable F2 and F3+ centers. Properties of photoluminescence at room temperature were studied. It shows that active channels (F2 and F3+ centers) with sizeable optical gain and a substantial increase of the refractive index are promising for the realization of active optical waveguide devices which are tunable in the visible.关键词：LiF thin films;color center;optical waveguides135|72|0更新时间：2020-08-11
- 摘要：At first we stress that a successful fit result is determined by three factors, namely the high-resolution spectrum data, effective computer program and skill for correctly undertaking curve fitting. The latter two factors are considered in this article. The algorithm of curve fitting are based on the damped least squares optimization methods. It is programmed in FORTRAN 77.The general principles of a satisfactory optimization routine are given in the context of degree of convergence and the computation time needed to achieve an acceptable fit. The computer programs developed are capable of separating 24 overlapping bands at the most in a composite profile having 500 experimental data points. In the case of a composite profile strongly perturbed by the shot noises, a weighting function must be introduced into the computer program for its effectively running. Corresponding to the shape of a profile (a smooth curve or a curve revealing a high-level of noises) and the constraint conditions, one may use a suitable program to undertake curve fitting. The functions of six programs are listed in Table 1. Furthermore, we stress that the mere ability to undertake the required calculations, in terms of rapid data handling capability of the computer, is not the guarantee that meaningful fits will be obtained. It is shown that a preliminary data processing is needed. In order to eliminate "insensible parameters" during the fitting calculations we should make the conversion of the values of original data. The value of abscissa for every point should be converted into the value expressed in the unit of meV. The value of intensity for every experimental point must be converted into a value as the maximum intensity is set at 100 a.u .Curve fitting may be facilitated if the initial estimates of parameters were chosen appropriately. The peak energy position must be accurately fixed. The discrepancy of a fit may be employed to locate any regions of poor fit in conjunction with visual plot. The regions of poor fit are attributed to incorrect choice of the initial estimates of parameters or the incorrect fit model adopted. A successful fit result is determined by the fit model which include the number of peaks, peak energy position and degree of band asymmetry. These factors are discussed in detail.At last we have exemplified the curve fitting of the 25K luminescence spectrum involving NN1-bound exciton in GaP:N sample. We have shown how to undertake the curve fitting of the whole composite profile, how to locate the region of poor fit and to change the fit model, and finally achieve a reliable fit.关键词：luminescence spectrum;curve fitting84|72|0更新时间：2020-08-11
- 摘要：Research in measuring and evaluating method of LED visual display panel is presented. Both subjective and objective facts should be considered to evaluate efficiently the main parameters of LED panel so as to make a conclusion to LED panel display quality.Through the analyzation of the indispensable parameter in the LED panel display quality,the research method is determined.On account of subjective perception on the scheme of the watching and detection experiment,the research emphatically focus on as follows:the establishment of simple appraising way,the model of chroma space,perceptive stimulative algorithm,analysis of the parameters ect.Aimed at nonstandard complication of LED quality evaluation,this paper presents a simplified measuring and evaluating theory for LED visual image quality evaluation based on physiology.For verification the correctness of the theory,the measurement tests of various LED display panel have been done,and it is proven that it resolves many problems arised in LED measurement and evaluation.关键词：LED;parameters measurement;evaluating method118|71|2更新时间：2020-08-11
- 摘要：Wide band-gap semiconductor materials are of considerable interest for their important use in blue and ultraviolet optical devices such as light emitting diodes and laser diodes. In 1997 the ultraviolet laser emission of ZnO film at room temperature was reported.Then the random laser from nanosize ZnO power was also announced.After that this material has attracted a lot of scientists. And high quality ZnO films were grown by different methods such as MOCVD and MBE. We have obtained high quality ZnO films by reactive DC sputtering on Si(100) and Si(111) and observed its superlinear ultraviolet emissions.In order to compare the properties of ZnO films made by different methods,our team prepared ZnO films on Si(100) by electron beam evaporation.We wanted to gain polycrystalline films by this method.A serial of ZnO films has been obtained successfully by changing the speed of growth.All the samples were annealed in air at 950℃ for 1h. From the X-ray diffraction pattern it was found that some films had very strong c axis orientation.But the orientation disappeared as the speed of growth became very high. The surface of film was observed by scanning electron microscope.From the picture one can see the crystallite grain with size around 150nm. At last the PL spectrum (210nm excitation) of the ZnO grain films was measured.The emission spectrum showed strong green band peaked at 525nm.The intensity increased with increasing the speed of growth.Because the high speed growth can create more defects,this result showed the emission of green light might be caused by defects. Recently, research efforts were usually focused on the blue emission and ultraviolet emission.We will try to obtain them by changing the conditions of growth and anneal of ZnO films.It was reported that the excitation spectrum of ultraviolet emission (390nm) peaked at 195nm.It’s better to excite ZnO films with Synchrotron Radiation shorter than 200nm.132|104|3更新时间：2020-08-11
- Address：No.3888 Dong Nanhu Road, Changchun, Jilin, China Postal code：130033
- Tel：0431-86176862 Email：fgxbt@126.com
- Technical support is provided by Beijing Founder electronics co., LTD 吉ICP备11002662号-17
京公网安备11010802024621 - It is recommended to read the content of this site in Chrome&IE9+. Please switch to extreme mode in browser 360.
- Cookies We use cookies to help provide and enhance our service and tailor content. By continuing, you agree to the use of cookies.
0