最新刊期
卷 8 ， 期 1 ， 1987
- 摘要：The Hamiltonian describing a rare-earth impurity ion is assumed to be composed of the free ion Hamiltonian HF and the one-electron crystal-field Hamiltonian HCF·We write HCF=V0+H’CF with
here V0 is the part of HCF that is independent of angular variables.Thus the Hamiltionian of the system can be written as H=HF+V0+H’CF (3)The eigenvalues of HF+V0 are usually called free ion levels. Because of the existence of H’CF, each free ion level will split into Stark levels, and the center of gravity of the Stark levels will be shifted from correspondent free ion level. It is not concluded whether these shifts are comparable with the contributions of configuration interaction, spin-spin interaction and other interactions. The systematical calculation on these shifts has not been reported so far as we know. In this paper we present the results for Er3+ in Y3Al5O12. 103|34|0更新时间：2020-08-11 - 摘要：By two ways the impurity Li was diffused into CaTe crystals. The anneal of sample a was made in a quartz tube at 350℃, under Te atmosphere for 320 hours. Li diffusion was made from Li2CO3 solutions deposited on the polished wafer surface in a horizontal furnace, under a continuous flow of H2-N2 mixture. The temperature was 350℃, and the diffusion time was one hour. Li diffusion of the samples b and c was similar to that of sample a but without the first stage. The temperature was 450℃, and diffusion time one hour and 0.5 hour respectively. The second way without prediffusing of Te is reported first time.In order to investigate the interaction of ALi° with electrons and excitons in CdTe:Li, the dynamic processes of various luminescence mechanism were analysed. The effect of excitation intensities of (e, ALi°) and (ALi°, X) emission were observed at UK. And two relationships, Ilum-Iexc and Ilum-Iexc1.5 were obtained respectively. A bound exciton (ALi°, X) could be dissociated thermally into an electron and a hole leaving a neutral acceptor ALi°,(ALi°,X)→ALi°+e+h. By fitting the curve to the experimental data of the integral intensities in (ALi°, X) emissions, we got that the bound energy of exciton was about 4meV.The electron-phonon coupling for various Iexc in (e, ALi°) was analysed. When the trapped centres are the same, N, the mean number ofemitted phonons is a constant. And N is a measure of the radius of the trapped carrier wave function if the charge distribution of trapped carriers can be approximated by a Gaussion function. The constant a characterizing the localization of the carrier at a centre is about 160Å.102|49|0更新时间：2020-08-11
- 摘要：Implantation of rare-earth ion into ZnSe and ZnS crystals has been used to fabricate light emitting diodes[1-4]. ZnS:Er, Nd MS diodes also have been fabricated which give different colours of electroluminescence emission when the efxcitation parameters are changed[9]. In this report, the variable colour ZnSe:Er3+ MIS diodes are depicted which are made by means of effective luminescent centers under high[5,8] and low[7,8] electric field excitation, as shown in Fig.1.ZnSe crystals were grown by sublimation method. The dice with demen-sions of 6×6×1 mm3 were annealed in the molten zinc to reduce their resistivities to the range of l-10Ω·cm. Erbium ions with energy of 100keV and dose of 1×1015cm-2 were implanted into ZnSe substrate at room temperature. Annealing was performed in the molten zinc to eliminate the radiation damage[11]. After annealing, an In ohmic contact was made on the substrate. A thick layer (-600Å) of ZnSe was deposited on the implantation surface by evaporation and finally a circular gold electrode (1 mm in diameter) was evaporated on the top of ZnSe layer.Fig.2 shows electroluminescence spectra of the variable colour ZnSe:Er3+ MIS diodes. It is easily found that the diodes give green electroluminescence of Er3+ when reverse biased, and give near band edge emission in blue when forward biased. The luminescent colour is changed with the polarity of applied voltage in this kind of diodes.The luminescent mechanism of the diodes is the high field direct impact excitation when they are reverse biased[2-4]. And the blue near band edge luminescence under forward bias could be explained by the hot holes injection[10], as shown in Fig.1.137|37|0更新时间：2020-08-11
- 摘要：For the advanced study of the luminescence of Ce3+ in various coordination environment served as are activater or sensitizer, the luminescence and energy transfer phenomena in hexagonal-NaLnF4 (Ln=La Gd or Y) doped with Ce3+, Ce3+-Tb3+, Ce3+-Eu3+ have been investigated and some results are reported in this paper.The same luminescence centre of Ce3+ formed in NaLaF4 and NaYF4 and the higher energy transfer efficiency of that in the host lattices are suggested from the fact that in the two host lattices Ce3+ emits near 300nm with the close luminescence intensity and that the quenching concentration is very low for Ce3+ in the flouride.A broad band with a max. emission peak at 420nm was observed in the host lattice of NaGdF4 and the doped NaGdF4:Ce3+ under the excitation of 273.5nm (Gd3+ 6p-8S) and 250nm (only for NaGdF4 at 77K and room temperature). Comparing the excitation and the emission spectra of NaGdF4 and NaGdF4:Ce3+, the relationship between the concentration of Ce3+ and the luminescence intensity of the broad band and Gd3+ in NaGd1-xCexF4 (x=0, 2.5, 3.5, 1) and the results-reported in some referencesthat the cation-defect centre or electron-self-trcped hole centre could be observed in some flou-rids especially containing Gd3+ which could provide a shallow trap for electron, we suggest that one kind of cation-defect centre may exist in the NaGdF4 host lattice (broad band emit in 420nm) and be sensitized by Ce3+ and Gd3+ through the pathway from (Ce3+→Gd3+) to cation-defect centre.104|30|0更新时间：2020-08-11
- 摘要：La2SO6(LS), Gd2SO6 (GS) and Y2SO6 (YS) were prepared by a flux method in a reducing atmosphere. They are of the same type of structure, orthorhombic,with the space group I222, and the site Symmetry of Ln is C2.The luminescence of Ce3+ in them was studied v/ith their excitation spectra and emission spectra.The spectra of GS:Ce3+ and YS:Ce3+ are quite similar as expected, whereas those of LS:Ce3+ show marked differences.The excitation spectra of the samples prepared by codoping Ce3+ and another emission center which can be sensitized by Ce3+ e.g. Dy3+ in these three hosts monitored at Dy3+ emission line, show very similar behavior (Fig.2).The excitation peaks due to Ce3+ in GS:Ce3+, Dy3+ and YS:Ce3+, Dy3+ coincide with those of GS:Ce3+ and YS:Ce3+ in Fig.1, whereas the peaks located at-300nm and-330nm in LS:Ce3+,Dy3+ have no correspondence in LS:Ce3+. But it was argued that these two peaks also originated from Ce3+ and this was affirmed by diffused reflection spectrum of LS:Ce3+ (Fig.3).Hence the luminescence of Ce3+ in LS might be described as following:the 5d manifold of Ce3+ are split into 5 levels, in conformity with C2 site symmetry, three of them are obtained directly from the excitation spectra of LS:Ce3+, the other two are obtained from the excitation spectra of a center sensitized by Ce3+ or from the deffused reflection spectra and the emission is originated from the next lowest 5d state.Here it can be argued that two factors pertaining to the appearance of the uncommon emission from the next lowest 5d state are as follows. (1) small Stokes’ shift, and (2) narrower excitation peaks.109|40|0更新时间：2020-08-11
- 摘要：In this paper the synthesis method of Me2SiO4:Tb3+ (Me=Ca, Sr, Ba) is reported. The Me2SiO4:Tb3+ (Me=Ca, Sr, Ba) were fired at 950℃ for two hours using MeCO3, H2SiO3, Li2O3 and Tb2(C2O4)3 with suitable mole ratio, reground, and then retired in air at 1250℃ for three hours. Li+ ions were added to compensate charges. The crystalline phase was checked by a X-ray powder diffractometer. The excitation and emission spectra were measured by MPF-4 fluorospectrometer.The emission spectra of Me2SiO4:Tb3+ (Me=Ca, Sr, Ba) under UV excitation originate from 5D3-7FI and 5D4-7FJ transitions of Tb3+ ion. The strongest peak corresponds to the transition of 5D4-7F5, when the concentration of Tb3+ ion is 0.05-0.3mol. The difference between emission spectra of Me2SiO4:Tb3+ (Me=Ca, Sr, Ba) is small. The concentration quenching of the luminescence of Me2SiO4:Tb3+ is discussed. It is found that the variation in intensities of 5D4-7F5 and 5D3-7F5 transitions with the terbium concentration is of different trends. The optimum concentration of Tb3+ ion for Ca2SiO4:Tb3+ or Sr2SiO4:Tb3+ is about 0.15mol., and that of Ba2SiO4:Tb3+ is about 0.25mol.It is well known that the relationship between the luminescence intensity I and the concentration of activator x can be written as I/x=A(1+βθ/3)-1, where θ is a constant related to the interaction between activator ions, A and β are two parameters. We have found that 6 is equal to three for the transition of 5D4-7F5 and 6 for the transition of 5D3-7F5. This result means that the concentration quenching mechanism for 5D4-7F5 and 5D3-7F5 is different.98|40|0更新时间：2020-08-11
- 摘要：Zn is one of the accepor dopants for getting the hightest efficient radiate recombination centers in GaN[1]. It is reported that the different Zn concentration in Zn-doped GaN can provide emission colors of blue, green, yellow and red[2-4].So the problem non-uniformity of Zn concentration in the layer if GaN by VPE must be solved. Monemar et al[4]. have showed that Zn concentration was related to the position of substrate in a reactor chamber. High ohmic resistance Zn-doped GaN layer was not at the front of reaction zone but at some distance of the reaction zone. A typical variation in resistivity was a factor of 40 when the substrats were arranged in a region of 15 mm along the reaction zone. This behavior can partly be explained by the vari-arion of N-vacancy concentration in this growth direction. We have investigated a lot of samples of Zn-doped GaN. It was observed that the concentration of Zn was non-uniform in the VPE layers of GaN.Variant position for obtaining ohmic Zn doped GaN was different even on the same sample surface, resulting in different emission spectrum.This phenomena may connect with defects of grown GaN such as helical dislocation different morphology and growing pits on the GaN epitaxy layer surface.107|81|0更新时间：2020-08-11
- 摘要：The change of concentration, depth and capture cross section of deep level for p+-n GaAs1-xPx LED’s during degradation at large current (J=250A/cm2) for about 750 hours was investigated by DLTS techniques at room temperature, and their luminescence spectra, luminous fluxs and C-V and I-V characteristics were measured. The parameters of deep level before and after degradation are listed in Table 1.It was observed that there were three electron energy levels [△En1=0.19±0.01) eV; △En2=(0.20±0.01)eV; △En3=(0.40±0.01)eV] in GaAs1-xPx LED. No new deep level was found after degradation. The luminous efficiency of LED was reduced by 20-35% and then tended to be saturated during aging process, as shown in Fig.3. Experimental results show that the deep energy level density of △En1, △En2 is decreased, while △En3 is increased and its capture cross section is larger. Thereby the △En 1 of capture ration is relatively increased after degradation. As shown in Table 1 the proportion of capture probability of △En3 is increased, although total capture probability of the three energy levels remains almost constant. The capture probability of △En3 is increased by 9,15,26 and 30% respectively and 20% in average for 1#-4# LED’s. Whereas luminous effoiency is decreased about 21%. The results are agreed very well. This means that the decreace of luminous efficiency after degradation is mainly due to △En3 and △En1,△En2 do not influence the luminous efficiency and degradation characteristic at all. Fig.3 shows that the forward threshold voltage and reverse breakdown voltage of GaAs1-xPx LED are decreased after degradation. This means that p-n junction is damaged and the leakage current is increased with degradation. This may be one of the reasons for the reducing of GaAs1-xPx LED luminous efficiency.102|40|0更新时间：2020-08-11
- 摘要：In this report the degradation characteriscs of GaAs/GaAlAs DH LEDs were investigated.The GaAs/GaAlAs DH wafers were grown by LPE technique, the DH LED used in this study was consisted of four layers. The first n-Ga1-xAlxAs (x=0.35) buffer layer is 6μm thick. The second active layer p-Ga1-xAlxAs (x=0.05) is 1 μm thick. The third p-Ga1-xAlxAs layer is 1-2 μm thick, and the last contact layer is p-GaAs, 2 μm thick. The output power is above 1 mW. The output power of the tail fibre (inner diameter 60 μm, NA=0.17) is above 60 μW.The degradation characteristics of the devices were investigated at room temperature with inject current of 100 mA. During ageing dark defects in LEDs were observed with an infrared line scanning.The effect of operation time on the P/P0, I-V characteristics and EL pattern was investigated. The results shown that there are two degradation modes. The slow degradation of the LEDs are due to the dark defects(DSD) grown in the action layer of LEDs.The degradation characteristics of GaAs/GaAlAs and InP/InGaAsP DH LEDs were compared. The result indicated that the degradation mechanism for GaAlAs and InGaAsP DH LEDs is different.101|55|0更新时间：2020-08-11
- 摘要：Photoelectron yields of fast and slow decay components corresponding to 220 nm and 300 nm emissions in BaF2 luminescence have been measured respectively. By means of the fast decay component of 220 nm emission,a BaF2 detector with both high time resolution and high counting rate has been developed. Application of our BaF2 detector to positron annihilation lifetime spectrometer to replace the plastic crystal scintillation counter improves the time resolution from FWHM=270 ps to FWHM=19.0 ps or increase the counting rate by ten times.Laval et al. discovered that there is a fast decay component with the lifetime of 0.6 ns at the wavelength 220 nm in BaF2 luminescence in addition to the slow decay component with the lifetime of about 600 ns at the wavelength 300 nm. The time resolution of the BaF2 crystal obtained by means of the fast decay component can be compared with that of the plastic scintillation crystal NE111. On the other side, the BaF2 crystal, containing heavy element Ba, has the ability to effectively gamma-rays, and so, the BaF2 detector has high detection efficiency.94|46|0更新时间：2020-08-11
- 摘要：By making use of the modified unitary transformations the effective Hamiltonian and effective mass of the exciton are given. The binding energy of the exciton for some polar crystals is calculated, which is given in Table 1.115|46|0更新时间：2020-08-11
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