最新刊期
卷 7 ， 期 2 ， 1986
- 摘要：In this paper, the theory and method of energy level calculation of rare earth ion in crystals, were reviewed.First of all, the physical thoughts and physical actions were described,then,the mathematical methods of calculating physical action were inducted.246|107|0更新时间：2020-08-11
- 摘要：We have investigated the EPR spectra of LaOBr:Ce3+,Tb3+ powder at liquid helium temperature(4.2K).The EPR signals of three samples with differential concentrations of Ce3+and Tb3+have been obtained on the X-band at 4.2K.The measured results are as follows:ion sample1 2.3Ce3+ g=2.440 g=2.457Tb3+g=3.110 g=3.125The EPR spectra of LaOBr:Ce, Tb powder are computed according to crystalline field theory.The crystalline field Hamiltonian of LaOBr:Ce3+ Tb3+ crystal is computed by means of point charge model.Using Stevens’“Operator Equivalents”method,we have obtained the crystalline field Hamiltonian operator:where Amn=-|e|γnm const are known as the “crystal field parameters”, and γnm are coefficients which are related to the crystal structure.The particular form of for LaOBr:Ce3+Tb3+is: Using the Hamiltonian operator, we have computed the energy level splitting of Ce3+ and Tb3+ ions in LaOBr crystal by perturbation theory at representations |LzSz| and |JJz| respectively.On this basis the values of g-factor of Ce3+ and Tb3+ ions are obtained:g=2.487 for Ce3+iong=3 for Tb3+ ionAccording to the theory of Ibers ’et al., through analyzing the line shape of powder EPR spectra.It is verified that the factor of crystal is almost equal to the that of LaOBr:Ce3+Tb3+powder.The calculated result agrees very well with the experimental result.It is thus affirmed that the dopant Ce3+ and Tb3+ions substitute La3+ ions in host material and form luminescence centers.105|41|0更新时间：2020-08-11
- 摘要：It is interesting to investigate the characteristics of luminescence in GaP crystals doped with two kinds of isoelectronic impurities Bi and N.In the present paper, the experimental evidence for exciting energy transfering from N-and NNi-traps to Bi-traps is presented for the first time.Photo- luminescence measurement had been carried out for GaP epilayers under the excitation of 4880A radiation from an Ar-ion laser in the temperature range of 4.2-147K.The PL spectrum were presented which were recorded from GaP:Bi at 4.2K phonon sidebands of the BBi-line, and there were not ABi-line, its phonon sidebands, and the BBi-line.The 4.2K spectra of many GaP-crystals doped with N and Bi were similar to that of GaP-crystal doped with Bi alone.Although the crystals used in these measurements contained nitrogen with a concentration of about 1×1018cm-3, in general the AN-line and NNi-lines were hardly seen in the 4.2K spectra.In the temperature range of 50-77K these lines could only be recorded by radiation detecting system with a higher sensitivity for most of the samples.On the other hand, the EL spectra of LEDs of GaP:(Bi,N) at room temperature showed both N-green emission band (peak) and Bi-emission band (shoulder).Therefore it is reasonable to suggest that there is an exciting energy transfering from N-NNi-traps to Bi-traps to Bi-traps at low temperatures.Based on the experimental results a dynamical model was proposed.The intensity of Bi-emission band iswhele, G is a constant depending on the number of Bi atoms in GaP:(Bi,N), and excitation density.The termrepresents the energytransfer from N and NNi-pair centres to Bi centres due to tunneling and thermal dissociation.The competition between radiative transition and thermal quenching are represented by 1 and Ae-Ea/kT in denominator.It was pointed out that the energy transfer due to exciton tunneling from N centres and NNi-pair (i≥3) traps to Bi traps was predominant at temperatures below 40K and the energy transfer from N and NNi-pair centres to Bi centres due to thermal dissociation predominated above 40K.Above a certain temperature both the two kinds of energy transfer decreased, so that the intensity of AN and NNi-line in the spectra increased with the temperature for the ability of Bi centres to bind excitons had dropped.This formula was used for explaining the temperature dependence of the ratio of the intensity of Bi-emission band in GaP:(Bi,N) samples to that in GaP:Bi sample.128|72|0更新时间：2020-08-11
- 摘要：Energy transfer from Ce3+ to Tb3+ in various hosts has been normally observed.We report, in this paper, that the energy transfer in the reverse direction, i.e.from Tb3+ to Ce3+ in CaS: Ce,Tb phosphor.Excitation spectrum of 500nm emission of Ce3+ in CaS:Ce consists of two bands.The band peaking at 280nm corresponds to the excitation host and that at 450nm relates to the 4f-5d transition of Ce3+.The excitation spectrum of 436nm emission of Tb3+in CaS:Tb consists of the 280nm band as well as a band at 320nm, which is a characteristic of Tb3+.For CaS:Ce,Tb,however,the excitation spectrum of Ce3+ emission at 505nm also consists of the 320nm band.This indicates that the excitation energy may be transferred form Tb3+to Ce3+.Under the excitation of 320nm, CaS:Ce, Tb gives emission both from Ce3+ and Tb3+ and the intensity of Ce3+ emission increases with the concentration of Tb3+.The enhancement of Ce3+ luminescence by codoping of Tb3+ can be as large as 3 times.The decay time τc of Ce3+ luminescence in CaS:Ce is less than 1 Us.The decay of Tb3+ in CaS:Tb consists of a fast decay component τT1=80μs and a slow one τT2=1400μs, the Tb3+ concentration being 3×10-5mol.It can be seen that the decay of Ce3+ emission in CaS: Ce,Tb has now a slow component, very similar to the decay of Tb3+ luminescence.On the other hand, the decay of Tb3+ emission depends on the concentration of Ce3+.All these results imply that the energy is non-radiatively transferred from Tb3+ to Ce3+.Owing to the overlapping of the excitation spectrum of Ce3+ emission in CaS:Ce and the emission spectrum of CaS:Tb, we believe that the energy transfer is a reasonable process.128|48|0更新时间：2020-08-11
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THE POLARIZATION PROPERTIES OF THE RECOMBINATION EMISSION OF BOUND EXCITONS IN EPITAXIAL GaN CRYSTAL
摘要：The polarization properties of the three kinds of bound excitons bounded at neutral donors(BED0) neutral acceptors(BEA0) and Donor-Acceptor pairs (D-A) in GaN crystals were studied.The polarizability of the emission of BED0 and BEA0 increases quaduatically with the increase of the excitation intensity (Iex) in the range of 104W/cm2~106W/cm2.And a saturation appears thereafter.The initial polarization of the photoluminescence from BED0 and BEA0 can be explained by the anisotropic dielectric constant of uniaxial crystal.And the change of polarization with the Iex is due to the different extent of the dipole-dipole interaction between bound excitons at different density.The GaN crystal layers were grown by the VPE on sapphire substrates oriented in the (0001) direction.The samples were put in the crystal ESR-900 and cooled down to 77K.And they were then excited by a light beam of wavelength of 308nm from an excimer laser EMG-102.With a set if neutral attenuators and a lens, Iex on samples could be easily changed from 104W/cm2 to 107W/cm2.A polarizer was put before a double grating monochrometer to pick out bound exciton emissions polarized in parallel and vertical directions to the C-axis of GaN wafers respectively.After the monochrometer, the light signal was messured by a photomultiplier C-31034 with cooling system and recorded by a X-Y recorder.Fig.1 and Fig.2 show the emission spectra of different samples.Fig.3 shows the optical scattering plane in experimental setup.Fig.4 and Fig.5 show the P values under different Iex for different samples.Therelations of BED0 and BEA0 are shown in Fig.6 and Fig.7 respectively.From Fig.6 and Fig.7,we can see that the ralation P=(A+BIex)2(7)is valid in the Iex range of 103W/cm2-105W/cm2.When Iex is higher than 105W/cm2, P tends to a saturation point.It might be caused by the concentration limitation of neutral donors and neutral acceptors.139|73|0更新时间：2020-08-11 - 摘要：Implantation of rare-earth ion into ZnS and ZnSe has been used for fabrication of LEDs with MS structure.The implantation processes were carried out by using an ion beam energy of 20keV and with the substrate at 77K.In the present experiments, erbium ions were implanted into ZnSe with the substrate at 300K.After annealing the ZnSe:Er3+ crystal in N2 atmosphere, ZnSe:Er3+ LED with MIS structure was fabricated.According to the reason of I layer forming, we first proposed that the I layer could be eliminated by annealing Er3+-implanted ZnSe crystals in melten zinc and the LED with MS structure could be fabricated.ZnSe crystals were grown from the vapour phase in sealed capsules con-tainting slight excess of zinc in our laboratory.Dice with dimensions of 6×6×1mm3 were annealed in melten zinc to reduce their resistivities to the range of 1-10Ω·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 N2 atmosphere or in melten zinc, respectively.105|38|0更新时间：2020-08-11
- 摘要：The result of photocapacitance measurement on background deep levels in ZnSe is reported.A short discussion about the principle of photocapacitance technique used in this work is presented.In the case that there is only one deep level located within the upper half of the gap and its concentration NT is much smaller than that of the shallow impurity ND,the capacitance transient is a single exponential one.In the case that more than one deep levels exist,the transient is a multi-exponential one When m=2 the individualΔCi(∞)and Ti can be determined by multi-regression procedure.113|67|0更新时间：2020-08-11
- 摘要：Cerium is more abundant and cheaper than the other rare earth elements.The Ce3+ luminescence is due to a f-d transition with a broad emission bands.Its decay time of the fluorescence is very short, usually in the range of 30-100 ns.The phosphors with Ce3+ ion find applications in cathodolu-minescence and photoluminescence, and they are scintillator materials.So people havebeen interested in Ce3+ luminescence.The Ce3+ luminescence varies strongly with host lattice and local surroundings.The energy transfer and sensitization had been studied between Ce3+ and Ln3+ ions in several materials.131|38|0更新时间：2020-08-11
- 摘要：The phosphor BaSi2O5:Pb2+ has been widely used in manufacturing of black light lamps.However, the detailed information about its preparation can not be found in the literature.The aim of this research is to work out the optimum conditions for preparing BaSi2O5:Pb2+ having efficient emission in ultraviolet.A solid state reaction between barium carbonate and silicic acid in the presence of activating agent PbO2 and some fluxes was studied with the aid of orthogonalizing method of the experimental design.The optimum reaction conditions are found to be as follows.The excess silicic acid must be used to inhibit the formation of other barium silicates so as to ensure the product being of a sanbornite structure.The mole ratio of SiO2/BaCO3 is 2.3-2.8.The activating agent, lead oxide, should be added in a large amount.The mole ratio of PbO2/BaCO3 is 0.04-0.17.Because of the volatility of lead oxide at high firing temperature.some loss of lead occurs.The actual concentration of divalent lead remained in the phosphor is determined to be about 0.8 mole by atomic emission spectroscopy.The addition of fluxes BaF2, BaCl2 and BaSO4 promote the solid reaction.Firing should be proceeded at the temperature above 1100℃The excitation and emission spectra of BaSi2O5:Pb2+ obtained in our laboratory are studied and they are as same as the commercial products.Furthermore, its integration intensity of luminescence is higher than that of the commercial phosphors and is evaluated to be 108% of that of Toshiba phosphor SPD-8S.110|35|0更新时间：2020-08-11
- 摘要：LEDs for application in long-haul optical communication system are characterized by their high effective radiance and the long-term reliability.Although diodes having hemispheric or spheric lens on the emitting surface exhibit higher external efficiencies,but such devices are too expensive to make for this application purpose.Therefore in the present work, we investigated the effect of front facet sputtered A12O3 coating on light output increase of In GaAsP-InP LED.A conventional RF sputtering equipment with the source power 3kW at 13.5MC was used in deposition of A12O3 AR coating.A high purity A12O3 disk was employed, as target.The calulated results show that reflectivity of A12O3 AR coating on InP surface is very low.It’s coefficient of thermal expansion (α=6.8×10-6℃-1) is approximately comparable to that of In P (α=4.5×10-8℃-1).In order to eliminate possible second electrons bombardment on devices during deposition of A12O3 coating.It is necessary to modify the sputtering equipment to provide a “region without damage” on the surface of the substrate table where diodes are placed for A12O3 coating.103|40|0更新时间：2020-08-11
- 摘要：This paper discussed in detail some essentials on the Time Correlated Single Photon count technique (TCSP), which includes principle of statistics, problems which should be noted in measurement and the estimation of basic technique.When the sample is excited, photon emission should satisfy the following conditions.(1) STABILITY: Time probabilities are fully the same in photon emission process, after the sample is excited.(2) PARTICULATE PROPERTY: Statistical distribution between neighbor excitations is irrelevant.(3) GENERALIZATION: Let (t) represent the probability of the emission of two photons in the range [0,t].Iflim (t)/t=0is satisfied, PT(k), the probability of the emission of k photons in the interval T, is Poison distribution.121|91|0更新时间：2020-08-11
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