最新刊期
卷 23 ， 期 3 ， 2002
- 摘要：Progress in the scintillator luminescence research is summarized in this paper.The summary is concentrated on luminescence mechanism of the scintillators used for high energy physics in near future.New scintillators we have studied include BaF2,BaF2:RE,CeF3,PbWO4 crystals.Some new results on their luminescence mechanism were presented as follows: (1)Quantum cutting effect in Gd3+ and Eu3+ doped BaF2 powder has been observed,and its double photon emitting efficiency was about 190%.Based on BaF2 luminescence from "valence band → core band" transition,possible multi photon emitting from RE3+ in this kind of fluoride system has also been considered.(2)Temperature dependence of energy transfer from Ce3+ (emitting 290nm band) to defect luminescence centers (emitting 340nm band) in the CeF3 crystals was studied at 61nm (VUV) excitation.The energy transfer was confirmed by the excitation spectra of 290nm,240nm emissions and luminescence decay curves for 340nm emission at different temperatures.At 5K,the excitation spectra of 340nm emission were quite different from that of 290nm emission,but they were almost the same shapes at 350K.Under 61nm excitation,the decay time of 340nm luminescence was postponed from about 20ns to 40ns with rising temperature from 5K to 350K.The energy transfer efficiency was rapidly increased with rising temperature from 5K to 350K.(3)The "WO42-+Oi" defect as green emission center in PbWO4 crystals was proposed and instead of "WO3+F" center.The evidences of the view point about the "WO42-+Oi" green centers were offered by the emission spectra and EXAFS data for O2 or air annealing PbWO4 as well as the results of theoretical calculation of electron states for the "WO3+F" and "WO42-+Oi" centers.关键词：scintillator;BaF2;CeF3;PbWO4;quantum cutting217|117|4更新时间：2020-08-11
- 摘要：Prions in SrAl12O19 occupy highcoordination sites,hence experience a weaker crystal field environment.The 4f21S0 level lies below the 4f5d configuration,photon cascade emission has been reported.Photon cascade emission process also provides a unique method for directly measuring the quantum efficiency (QE)of 3P0 in this material.Since the separations between the Stark levels of 1I6,3P1 and subsequently 3P0 are small,it is reasonable to assume that the depopulation of 1I6 is dominated by multiphonon relaxation.All the electrons from 1S0 down to 1I6 would relax to 3P0 afterwards.The 1S0→1I6 fluorescence intensity can be taken as a measure of the initial 3P0 population.Thus the QE of 3P0 can be written as η(3P0)=photon number of photons emitted from 3P0number of electrons arrived at 3P0=intensity of all the emission lines from 3P0 intensity of the emission 1S0→1I6=I(3P0 - 3H4)βI(1S0- 1I6)=Rβ, where β is the branching ratio of the 3P0→3H4 transition.The emission spectrum within 370～520nm of the 1% sample is shown in Fig 4.The excitation wavelength being used is 205nm.The ratio of the 3P0→3H4 and the1S0→1I6 emission intensities,R,can be obtained from the spectrum.QE can then be derived from η=R/β.In Table 1 we listed the measured QE of some samples with different Pr concentrations or grown from different raw materials.For comparison,we also listed the result measured in CaAl12O19:Pr,Mg.As it is shown,QE decreases with increasing of Pr concentration.This reflects the effect of concentration quenching.It should also be noted that even in dilute sample,QE is still remarkably less than 100%.This might be the result of thermal excitation of the1I6and 3P1states.In fact,in the spectrum measured at room temperature,we do observe 3P1→3H5 emission peaked at 525nm (B in Fig.1).Besides,there are also other lines (b,c in Fig.5) appear as the temperature rises from 77K to room temperature,which may be attributed to the emissions from 3P1 or 1I6.According to the Stark levels given in Ref.,at room temperature,approximately 32% of the electrons would be at 1I6,while 7% at 3P1.And it is estimated by Judd Ofelt analysis,comparably great part of the 1I6emission intensities falls into infrared.关键词：quantum efficiency;photon cascade emission;trivalent praseodymium ions90|58|2更新时间：2020-08-11
- 摘要：Based on the difference between the inorganic composite and the organic composite,one of the softchemistry synthesis method(sol-gel process has been employed to prepare the rare earth/polymer hybrid materials.SiO2 with good photostability and thermalstability was used as the inorganic composite and acrylic acid series e.g.methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) with the almost same refractive index as SiO2 as the organic composite.In the presence of coupling agent 3-(trimethoxysilyl) propyl methacrylate (MSMA),sol-gel method was used to prepare two kinds of hybrid matrix materials SiO2/P(MMA-MSMA) and SiO2/P(HEMA-MSMA).The experiment results show that inorganic network and organic network were formed in the matrix materials.Since there exists a strong chemical bond between the inorganic phase and the organic phase,no evident interface in the final materials was found.The particle size is less than 100nm,suggesting the materials belong to nanometer composites.Owing to the formation of inorganic SiO2 and the polymer at the same time in the matrix,the materials not only have good toughness but also decrease the thermal collection and photo loss.This kind of material is a promising matrix for the inorganic/organic composite materials.In order to overcome the drawback and limitation of pre-doped and post-doped method in the traditional sol-gel method and shorten the period for the preparation of optical functional materials,a two step sol-gel method was developed with hydrochloric acid as the acid catalyst and hexamethylenetetramine (CH2)6N4 as the base catalyst for the in situ synthesis of rare earthcomplex in the SiO2 matrix based on the characteristic of the sol-gel method and synthesis rule for the rare earthcomplex.Since (CH2)6N4 can generate hydroxyl groups gradually,the pH value was raised and accelerated the condensation reaction.In the meantime,this kind of reaction condition also favors the formation of rare earthcomplex.As a result of hydrolysis and condensation,the rare earthcomplex was synthesized and wrapped in the matrix.Using the two step sol-gel technique,in situ complexes of rare earth ion(Eu3+,Tb3+) with organic ligands such as β diketone,aromatic carboxylic acids and phen were synthesized in SiO2/polymer hybrid matrix.By doping of rare earthcomplexes into layered compounds zirconium bis(monohydrogenphosphate) (α-ZrP) and mesoporous material MCM-41,new luminescence assemblies were prepared.Because the interlayer spacing of α-ZrP is too small to let the rare earthcomplex molecules intercalate,the increasing the interlayer spacing is the prerequisite for the preparation of the assemblies containing rare earthcomplexes.P Methoxyaniline (PMA) was used to preintercalate into the galleries of α-ZrP and the interlayer spacing was increased and confirmed by XRD.Therefore,the assemblies containing rare earthcomplexes were prepared and demonstrated by XRD and UV visible spectra.Since the high energy vibration of the hydroxygen group will heavily quench the luminescence of the rare earth ion,the mesoporous material MCM-41 was modified by aminopropyltriethoxysilane (APTES) and thereby the assemblies containing rare earthcomplexes were made.The luminescence intensity of the assembly using MCM-41 modified by APTES was as 9 times as the assembly using the MCM-41 unmodified.Novel,covalently bonded hybrid materials of rare earthcomplexes with silica were prepared by using bipyridine,Si as one of the precursors,which reacted with the TEOS by hydrolysis and condensation in the presence of lanthanide ions.These researches provide new possibilities for the development of new luminescence composites with high efficiency and long lifetime.关键词：rare earthcomplex;hybrid material;assembly;luminescence95|80|8更新时间：2020-08-11
- 摘要：Because glasses have particular properties,for example it is easy to be fabricated into products with various shape in the range from bulk plate to fine fiber,and many key optoelectronic components,e.g.,amplifier,display and storage devices etc.are made of glass with special optical properties,therefore we think the studies on long lasting phosphorescent (LLP) glasses and glass ceramics are important in views of not only the traditional application of LLP materials,but researching of new optoelectronic materials and devices.This article introduces the study on a new kind of LLP material:Eu2+,Dy3+co-doped strontium aluminoborate glass-ceramic with a composition of 29% B2O3,28% Al2O3,43% SrCO3,0.1% Eu2O3 and 0.1% Dy2O3(mol%).TransparentEu2+,Dy3+co-doped strontium aluminoborate glass with the same composition was synthesized under a CO atmosphere at 1550℃ which didn’temit LLP,however,opaque glass-ceramic with LLP phenomenon was formed by appropriate heat-treatment to glass.The XRD and infrared analysis show that the main microcrystalline phase in the sample is SrAl2O4.The excitation spectrum of the sample shows a broad band peaking at about 366nm which is due to the f→d transition of divalent europium; the emission spectrum is alike with the long lasting phosphrescent spectrum,showing a band which peaks at 516nm attributed to 5d→8S7/2transition of divalent europium.Thus the LLP of the sample is due to the characteristic emission of Eu2+ion.The thermoluminescence spectrum consists of three Gaussian fitted components,which may indicate there exist three kinds of traps.When the glass ceramic is irradiated with fluorescent lamp with a power density of 1.2×104lx for 20 minutes,the luminance of the sample is 3.53cd/m210 seconds after stopping the irradiation,the chromaticity coordinates are x=0.2842,y=0.5772.After 5 hours of the irradiation,the sample still has a luminance of 0.01cd/m2.The phosphorescence can be seen in dark even 30 hours after the irradiation.The decay of the luminescence is a complex process that consists of three parts: a fast decay,a intermidate and a long decay process.We considered that the formation of SrAl2O4 micro crystal was essential for the LLP of glass ceramic,it was very possible that Eu2+and Dy3+ ions were incorporated in the SrAl2O4 micro crystal,thus the LLP of glass ceramic was emitted by Eu2+,Dy3+ co-doped SrAl2O4 micro crystal.However,directly proof showing the formation of SrAl2O4:Eu2+,Dy3+ was absent.We suggest the LLP is due to the recombination of trapped holes and electrons whichcan be thermally released from trapping centers at room temperature.However,further studied should be carried on the mechanism of the LLP of Eu2+,Dy3+ co-doped strontium aluminoborate glass ceramic,as well as the relationship between the treatment processing of glass ceramic and its phosphorescent properties.关键词：long lasting phosphorescence;glass ceramic;Eu2+;Dy3+99|176|6更新时间：2020-08-11
- 摘要：Laser properties of Er3+,Yb3+co-doped erbium phosphate glass pumped by 974nm,2W laser diode is reported in this paper.Continuous laser at 1.53μm was obtained at room temperature in this erbium glass.The effect of Er2O3 concentration and sample thickness on laser properties was investigated.0.13wt%,0.5wt% and 1.0wt% mean Er2O3 concentrations and 1mm,2mm and 3mm sample thickness were used.It is found the laser threshold and slope efficiency is strongly depend on sample thickness and Er3+ ion concentrations.At the same Er3+ ion concentration,the thicker the sample,the larger the laser threshold.Slope efficiency increases with the Er3+ ion concentration at the same sample thickness.At present the best laser properties are realized in glass with 0.5wt%Er2O3 concentration and 2mm thickness.In this glass 10.2% slope efficiency,118mW laser threshold and 43mW maximum laser output were obtained.The laser spectral range is from 1527 to 1533nm.The center laser wavelength is 1530nm.99|121|2更新时间：2020-08-11
- 摘要：KMgF3 which was typical cubic perovskite structure,was ideal material for searching for new solid state laser because of its several advantages: good homogenous optics,high thermal stability,low melting point,anisotropy and high optical transparency etc.Due to the broad forbidden band and weak crystal field intensity,KMgF3could stabilize low-valence rare earth ions,whichcould be used to further study refine spectra structure of these rare earth ions.Using a traditional high temperature solid state reaction,mild hydrothermal and bridgman stockbarger method,the KMgF3:Eu2+samples was synthesized.In the hydrothermal and single crystal samples,the 420nm emission peak besides the emission of Eu2+ at 359.5nm was observed.After the sample was annealed,the emission intensity at 420nm lowered about 30 times than that before annealing,but there still was the weak emission peak at 420nm.We drew a conclusion that the 420nm emission peak resulted from main color center and trace oxygen center.Combining the intensity change of theEu2+ emission at 359.5nm in KMgF3:Eu2+sample annealed before and after,we proved that the energy transfer fromEu2+ to color centers occurred.In addition,the relative oxygen content in crystal was calculated by means of the absorption spectra data.关键词：complex fluoride;defects;energy transfer;divalent europium89|120|1更新时间：2020-08-11
- 摘要：For the excellent properties such as high quantum efficiency,long persistence of phosphorescence which may reach 16h,no radiation,and good stableness,SrAl2O4:Eu2+,Dy3+ phosphors have indicated their good practical prospects.Preparation of the phosphors has been conducted from the beginning of this decade.The synthesis of this kind of phosphor generally requires high temperature (i.e.,1300～1500℃) by solid state reaction.The matrix composition,structure and luminescent properties of the phosphors could be affected under different synthesizing conditions,such as calcining temperature,soaking time etc.However,little attention is paid to their synthesis conditions,structures and properties.The present work was motivated by the possibility of acquiring optimal calcining technology parameters for the applications of the long-lasting phosphors.In this paper,the SrAl2O4:Eu2+,Dy3+ phosphors were synthesized by high temperature solid state reaction process at weak reductive atmosphere (4%H2～96%N2).The preparation conditions and their effect on the luminescent properties of SrAl2O4:Eu2+,Dy3+ phosphors have been investigated.Based on the XRD peaks,the powder phosphors were identified as SrAl2O4 phase,which is monoclinic (a=8.4424Å,b=8.822Å,c=5.1607Å,β=93.415°).The results proved that the phosphors synthesized at different temperature in this work are all α phase,and the little amount of doped rare earth ions (Eu2+:0.2mol%,Dy3+:0.2mol%) have nearly no effect on the SrAl2O4 matrix phase composition.The typical SEM micrographs of the sample synthesized at 1500℃ (Sample A) and the sample synthesized at 1300℃ (Sample B) implied that the clusters are spherical,porous and multi crystalline.The average grain sizes of Sample A and Sample B are about 14.4μm and 4.8μm respectively,calculated on the ball like particles.The excitation and emission spectra of the phosphors were measured and analyzed.At room temperature,both samples exhibit broadband excitation and emission peaks in the photoluminescence spectra.Three excitation peaks were observed in Sample A,since two shoulders at 327nm and 374nm in addition to the maximum at 430nm.The emission peak was at 518nm with a bandwidth of 70nm.Compared with Sample A,in Sample B,the excitation and emission spectra exhibit similar shapes,however,both of them shift to the blue side in the photoluminescence spectra.The excitation peaks were at 317,362 and 425nm; the emission peak was at 515nm with a band width of 68nm.The results indicate that the main peaks of Sample B,which has a smaller grain size than Sample A,intend to shift to shorter wavelength.The results indicated that the luminescence of these phosphors is due to 4f65d→4f7 transition of Eu2+.The observed discrepancy in shifting of main peaks may be attributed to the difference in the crystal field strength that Eu2+ experienced and inherited from different synthesis routes.关键词：phosphor;strontium aluminate;spectrum;crystalline structure88|81|6更新时间：2020-08-11
- 摘要：Recent development of field emission display (FED) device require searching for some new kind of phosphor material whichcan possess low excitation potential,chemical and thermal stability,long service life at highcurrent densities.YAGG:Tb phosphor has been used as an green phosphor for PTV application.It shows green emission with high brightness and good chromaticity under high energy electron beam excitation.The co activated lanthanon such as Ce,Dy,Gd was study separately and exhibited good brightness.We synthesize and carry on surface perfect the phosphor and try this phosphor to be used in low voltage range such as 0～3000V which is suitable for FED.The YAGG:Tb,Gd powder was synthesized by heating highly pure powders of Tb2O3,Ga2O3,Gd2O3,Al2O3,and other flux at 1400～1500℃ in the air.After that,acid and pure water was used to clean the phosphor.At last,polymer binder was used to film the phosphor.The emission peak of YAGG:Tb,Gd excited by electron ray was in 544nm similar with YAGG:Tb.Its relative luminescencent brightness change with voltage of electron ray was show in Fig.1.The properties of traditional green phosphor ZnO:Zn was used as standard.It can be seen that the relative brightness of YAGG:Tb is higher than that of ZnO:Zn at 0～3000V excited voltage and the dead voltage was similar with ZnO:Zn.It has not saturation situation as ZnO:Zn.Fig.2 shows the change curve of relative brightness of YAGG:Tb,Gd and ZnO:Zn with excited current density.YAGG:Tb,Gd also shows the good behavior.The YAGG:Tb,Gd was synthesized and improved with suitable method.After compared with ZnO:Zn,it was concluded that it will be more effective at strong excited condition.关键词：field emission display(FED);green phosphor;luminescent properties87|107|0更新时间：2020-08-11
- 摘要：A modeling of the electrical injection and the optical output of a typical high brightness LED indicates an important influence by top layer thickness.Not only the high reflective index of the top layer which limits the inner emitting angle of less than 16.6°,but also light area where the light emitted directly under the electrode will be total reflected back or be absorbed .As increasing the thickness at the top layer,the current spreads via diffusion and electrical density distributed uniformly on the whole emitting area,where most of the emitting area has been outside of the shade of the electrode.The thicker the top layer is,the easier for current spread and light to emit out.A method of high brightness light emitting diodes precisely design was provided in this paper.A current density function,which is symmetrical because the electrode is round,was deduced with perfect p n model.From the calculated curve of current density distribution,the one of 50μm top layer is more uniform than that of 5μm one.On other words,as increasing the thickness at the top layer,more current was spread outside of the shade of the electrode.LED optical output can be divided into edge emitting and surface emitting.A thick top layer is very useful for increasing LED edge emitting and decreasing no light area in surface emitting where was shaded by electrode.The calcu lated result shows that LED with a top layer between 49 and 98μm will make maximal optical output.The processes of electrical injection and optical out as basis,external quantum efficiency of LED with any thickness of top layer can be calculated.The theoretical calculated curve indicates external quantum efficiency vs.the thickness of LED top layer rise the slope sharply before 20μm,and then become a slight slope.If the top layer is thick enough,current in active layer distribution uniform completely,maximal optical output,and internal quantum efficiency being 1,the maximal external quantum efficiency of this type of LED is about 12.1%.关键词：HB LED;internal quantum efficiency;external quantum efficiency;current density distribution103|54|3更新时间：2020-08-11
- 摘要：Hemispherical Si nanoquantum dots have been formed by self-assembled growth on SiO2/c-Si substrates using low-pressure chemical vapor deposition (LPCVD).The n-type Si(100) wafers were used as substrates in this study.After conventinal wet-chemical cleaning steps,2.3nm thick SiO2 was grown on Si(100) at 1000℃ in 2% O2 diluted with N2.Si nanocrystals were self assembled on the SiO2 surface by LPCVD of SiH4 in the temperature range of 560～590℃.The SiH4 pressure was 0.27×102Pa and the deposition time was 1min.We have experimentally studied the changes of PL efficiency and peak energy of Si nanodots with its heights hc.The results indicate that the PL efficiency remains unchanged when heights h e of Si dots are smaller than 5nm,while it dramatiaclly decreases as hc exceeds 5nm.The PL peak energy shifts from 1.28eV to 1.43eV when hc decreases from 5.5 to 0.8nm.We present a light emission mechanism,e.g.,quantum confinement effect interface light emission center radiative recombination model.The model indicates that the photoluminescence is not caused by the band to band transition,but caused by the recombination through radiative centers exsisting in the Si/SiO2 interface region.Namely,the radiative centers might indirectly play a role for the photoluminescence.Since localized states exist in the Si/SiO2 interface region,which originate in silicon oxygen clusters act as radiative recombination centers.When electron hole pairs are genarated by laser excitation,they are trapped by the radiative localized states through thermalization process.Since the carrier thermalization to the radiative recombination,the centers in the nanodots are considered to be very slow and less sensitive to the dot size,the radiative recombination rate of photo excited carriers is almost constant for hc<5nm despite the enhancement of carrier transfer to the radiative recombination center by the quantum confinement effect.关键词：Si-nanodots;self-assembled growth;quantum confinement effect-interface light-emission center recombination model92|81|1更新时间：2020-08-11
- 摘要：Periodic multilayer structures fabricated by alternate deposition two different organic materials are recognized as offering unique electrical and optical functions promising for high performance and new functionality devices.Considering the application of organic multilayer structures to various optical devices including highly efficient EL diodes and lasers,it seems desirable to explore material systems with the typequantum-well structure which has been one of the basic structure of semiconductor optical devices.Three periods multilayer structure was fabricated,in which tris(8-hydroxyquinoline) Alq and 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole were alternate deposited.The structure of the specimen was: PBD/Alq/ PBD/Alq/ PBD/Alq/PBD,in which the thickness of Alq was 3nm and PBD was 5nm,respectively.From the configuration and the energy band diagrams,the structure of the specimen was like inorganic quantum well structure,so conveniently,it was called organic quantum well structure in this paper,where PBD act as barrier potential and Alq as potential well.The photoluminescence (PL) spectrum of PBD are largely overlapped with the absorption spectrum of Alq,suggesting the possibility of resonance energy transfer or Frster transfer from PBD to Alq.The PL spectrum of the quantum well structure shows only peak at 508nm,which is Alq luminescence.And in the photoluminescence excitation (PLE) spectrum detecting Alq,the peak at 330nm is most dominated,whichcorresponding the absorption of PBD.So,the PL and PLE spectrum of the specimen prove that the period multilayer structure could possess carrier confinement type Ⅰ energy lineup.Compared the PL spectrum of the specimen with that of the single layer of Alq (20nm),the emission peak is shifted to higher energy by 20nm and the full width at half maximum (FWHM) is narrowed by 25nm.The phenomena were contributed to the confinement effect of the quantum well structure.Being confined energetically in the narrow potential well,the possibility of the carrier possessing the higher energy states is enhanced and the diffusion of Alq exitons is suppressed,which induce the increase of the higher energy component and decrease of the lower energy component of the PL spectrum.So the PL spectrum is blue shifted and narrowed considerably.77|86|0更新时间：2020-08-11
- 摘要：Organic electroluminescent devices using fullerene C60 as a hole-injecting buffer layer with different thickness have been prepared.The structure of the device is ITO/C60/TPD/Alq3/LiF/Al(TPD: N,N-diphenyl-N,N-bis(3-methylphenyl)-1,1- biphenyl-4,4-diamine,Alq3:tris(8-quinolinolato)-aluminum).The driven voltage are higher at the same current density with the increment of C60 thickness.The driven voltages are 8.1V,8.4V,9.2V,10.3V for the devices with 0nm,12nm,16nm and 20nm thickness of C60 at the current density of 4mA/cm2,respectively.The effects of the thickness of C60 on the efficiencies of the devices are investigated.The device with 12nm C60 buffer has the highest luminance while the current efficiency is not the optimum for this device,because the current density for this device is much greater than that for the device with 16nm C60 buffer.The optimum thickness of C60 buffer,16nm,which produces the highest efficiency,is obtained.EL efficiency of the device,whichcontains 16nm C60 buffer,has been improved by about a factor of one in comparison with the device without buffer at the current density of 100mA/cm2.The undoped C60 with high resistivity and first ionized potential using as a hole injecting buffer layer blocks the hole injection at the interface of anode and hole transporting layer.As the buffer becomes thicker,the current density is suppressed by decreased tunneling of holes under opplied voltage.As a result,the current densities are reduced at the same driven voltage.In the devices,Alq3,which is an electron transporting and emissive layer,has a much higher electron mobility than hole mobility.Accordingly,in Alq3,electrons are majority carriers and holes are minority carriers.In order to obtain high efficiency in organic electroluminescent devices the balanced electrons and holes injected from the cathode and anode into the emissive layer is required.Electroluminescence efficiency is controlled by the hole injection from the TPD into the Alq3.Part of the driven voltage drops across the C60 buffer,resulting in acceleration of injected holes and more accelerated holes injected into emissive layer.Thus,the reason for the improvement of efficiencies for the devices with suitable thickness of C60 can be attributed to the more balanced carriers concentration in emissive layer.关键词：organic electroluminescence;C60 buffer;carrier balance;efficiency79|54|0更新时间：2020-08-11
- 摘要：The yellow complexes of Eu3+,1/2 Eu3+ and 1/2 Re3+(Re3+=Gd3+ or Y3+)with dibenzoylmethide (DBM) and 2,2-dipyridyl(Dipy) have been synthesized in anhydrous alcohol.The elemental analysis showed that their compositions are Eu(Dipy)(DBM)3,Eu0.5 Gd0.5(Dipy)(DBM)3 and Eu0.5 Y0.5 (Dipy)(DBM)3,respectively.Their infrared spectra were recorded on a Nexus 670 FT-IR spectrophotometer,the results indicated that the chemical bonds have formed by the rare earth ions with the two ligands.The luminescence spectra were taken on F-3010 fluorescence spectrophotometer.The measurement results showed that the excitation spectra are similar,the optimum excitation wavelength is at 425nm.The measurement results of the emission spectra of the complexes excited by 425nm light indicated that there are five groups of emission peaks for Eu(Dipy)(DBM)3,the first group peak at 5816nm,belong to 5D0→7F0 transitions of Eu3+ ion,the second group consists of two peaks,at 592.6nm and 598.8nm,belong to 5D0→7F1transitions of Eu3+ion,the third group peaks at 613.8nm and 619.6nm (5D0 7F2 transitions),the fourth peaks at 652.8nm (5D0→7F3 transitions) and there are two peaks at 694.8nm and 705.6nm in the fifth group,they belong to 5D0→7F4 transitions of Eu3+ ion.The fluorescence emission peak positions did not change obviously in both mixed rare earthcomplexes.The fluorescence emission intensity of 5D0→7F2 transitions is the strongest.Comparison with the values of determined (Id) and calculated (Ic)of 5D0→7F2 transitions of the complexes,the determined values of Eu0.5 Gd0.5(Dipy)(DBM)3 are 2091(613.6nm) and 1934(619.6nm),but for Eu0.5 Y0.5(Dipy)(DBM)3they are 2183(613.6nm) and 2014(619.6nm).Their calculated values Ic=1208(613.6nm)and 1155 (619.6nm),which are smaller than the determined values.These situations showed that there are sensitizations actions from Gd3+ and Y3+ to Eu3+ in these investigated rare earthc omplexes.关键词：dibenzoylmethide;2;2′-dipyridyl;Eu-Gd complex;Eu-Y complex95|57|3更新时间：2020-08-11
- 摘要：Since Ibachcarried out low-energy electron diffraction experiments on ZnO semiconductor surface,the properties of the surface polaron in crystals have been of considerable interest.Many investigators studied the properties of the surface magnetopolaron by the method of a perturbation,a Larsen’s,a linear combination operator,a variational,a Feynman’s path integral,and a Green function et al.The present author and co workers discussed the ground state energy,vibration frequency and effective mass of the surface magnetopolaron by the method of a linear combination operator and a Lagrange multiplier.Many of them mainly concentrated their attention on the ground state energy case.However,fewer works have been done on the research of the properties of excited state of surface magnetopolaron.In the early 1970s,the energy of the ground and the first internal excited state of the optical polaron calculated by Huybrechts.The first relaxed excited state energy of the free Frohlich polaron was evaluated using the Fock approximation of Matz and Burkey by Lepine.Chunetal.discussed the hydrogenic impurity binding energy of the ground and the excited state in a cylindrical quautum wire by using Landau and Pekar variational method.The effect of confined electron optical phonon interaction on the binding energies of the ground state and an excited state are calculated as a function of wire radius.Using a similar method to that of Gu et al.and minimizing the energies to determine the variation parameters Luetal.,calculated selfconsistently the ground state and the first excited state energy shifts of a polaron in a slab due to the interactions of the electron with the BO and SO phonons.The gound state,excited states energy and selfenergy change with temperature were investigated using Green function method by Qin et al..Following the perturbation theory of Bajaj et al.,the ground state energy of a bound piezopolaron is computed for ZnS,ZnTe and CdTe by Sivakumar et al..Extending this theory to the excited states,the LA phonon contributions to the Lamb Shifts in these piezoelectric semiconductors are obtained.The energy of the internal excited state,the excitation energy and the vibration frequency of the weak coupling surface magnetopolaron are calculated by using the linear combination operator and the unitary transformation methods.Two limiting cases are discussed.As an example,the numerical calculation for ZnSe crystal has been carried out.The results show that the excitation energy and vibration frequency of the surface megnetopolaron will increase with increasing the magnetic field.关键词：surface magnetopolaron;weak-coupling;excitation energy70|71|0更新时间：2020-08-11
- 摘要：Recent development in the process of oxide glass preparation by the sol-gel method which is an organic polymerization procedure based on the hydrolysis and condensation reactions opened the possibility to use these superior materials as an oxide matrix of organic dyes.RhB laser dyes,one of whose key problems in the investigation and application was the matrix which hosted the dye,were successfully embedded in SiO2 gels.Many aspects of dye doped SiO2 gels had been studied,but the photoluminescence(PL) during different periods of the sol-gel process and the effect of the refluence had not yet been reported.Those were the main problems that were involved in this series of experiments.The starting materials in all of the experiments were: tetraethylorthosilicate [Si(OC2H4)4,TEOS],deionized water[H2O],ethanol[C2H5OH],Rhodamine B(RhB),and nitric acid in which the ratio of the materials in volume was TEOS:C2H5OH:H2O=1:4:20.The addition of HNO3 making the pH of the solution equal to 1 was applied as catalyst for the hydrolysis of TEOS.TEOS was hydrolyzed and polymerized using refluence method at 60℃ for 2 hours.The sol thus obtained was highly transparent and then it was sealed for 10 days.Subsequently,dried gel was prepared by baking the sample at about 90℃ for 7 days.During the course,the PL spectra of different periods of the sol-gel course were measured by RF- 5301(PC) S (Shimadzu Corporation,made in Japan).The peaks of the PL of the embedded dyes exhibited red shift in the whole process while the intensity increased at first and then decreased.Another group of samples were made without refluence during the period of hydrolysis and polymerization process while all the other steps were the same.The PL spectra during the period of aging were also obtained.Red shift of the peak wavelength was observed while the degree of the shift without refluence was much stronger.关键词：the sol gel method;fluorescent spectra;SiO2 gels;Rhodamine B81|70|0更新时间：2020-08-11
- 摘要：The development of flat panel display devices such as field emission displays (FEDs) and vacuum fluorescent displays (VFDs) requires highly efficient cathodoluminescent materials.While many efficient sulfide based phosphors have been explored as possible low-voltage phosphors,the volatility of sulfur has prohibited their use in FEDs or VFDs.Sulfide-base phosphors often degrade under high energy electron bombardment due to dissociation of the cation sulfur bonds.Oxide phosphors offer potential advantage because of their superior stability under electron bombardment and excellent luminescent properties.ZnGa2O4 is an attractive oxide phosphor for low-voltage cathodoluminscence applications in VFDs and FEDs.ZnGa2O4 is a binary compound oxide consisting of ZnO and Ga2O3 with the formula AB2O4and has a cubic structure that can be viewed as a combination of rock salt and zinc blend structures,a normal spinel structure [space group is Fd3m(Oh7)].The optical bandgap of ZnGa2O4 is about 4.4eV.Like other wide bandgap semiconductors ZnGa2O4 exhibits a blue emission under excitation by both ultraviolet light and low voltage electrons.Activation with Mn2+or Eu3+ ions,the emission shifts to green or red.The citrate gel method allows preparation of highly dispersed mixed oxide at low temperature.This method involves the formation of a mixed ions citrate that due to the three ligand nature of the citric acid,resulting a transparent three dimensional network upon drying (gel).The pyrolysis of the gel yields a homogeneous mixed oxides.The method was widely used to prepare multicomponent oxides,such as superconductors.In this paper,we report the synthesis of ZnGa2O4and ZnGa2O4:Mn2+/Eu3+ by a citrate gel method.XRD,TG-DTA,and luminescence excitation and emission spectra were used to characterize the resulting products.The results of XRD reveal that the powders begin to crystallize at 500℃ and pure ZnGa2O4 phase is obtained at 700℃,which agrees well with the results of TG-DTA and FT-IR.This temperature is much lower than that (1200℃) by solid state reaction method.In the crystalline ZnGa2O4,the Eu3+ shows its characteristic red (613nm,5D0→7F2) emission with a quenching concentration of 5mol%(of Ga3+),and the Mn2+shows green emission (506nm,4T1→6A1) with a quenching concentration of 0.1mol%(of Zn2+).The luminescence mechanism of ZnGa2O4:Mn2+/Eu3+ is presented.Activator sensitization and host-to-activator energy transfer are suggested.关键词：citric-gel;luminescence;ZnGa 2O 4;sensitization88|50|9更新时间：2020-08-11
- 摘要：Silicon was a main material of micro-electronic devices.It was possessed of better advantage than other semiconductor materials.But semiconductor silicon was not regarded as one of candidates in optoelectronic materials because of its indirect bandgap and lower light efficiency.Thus its application in the luminescence material was restricted.For obtaining strong visible luminescence material,people have done more investigation.Recently the studies on the strong visible light emission at room temperature for the silicon based materials,such as porous Si,amorphous Si,RE-doped Sietc.,have brought about a public extensive attention in the silicon photo electronic integration.Some of rare-earth ions are the better light emitting ions,the method that rare-earth ion was doped into silicon by using ion-implantation was adopted by more and more people.The ion-implanted Si-based emitting materials are investigated for their light emission properties.Now,study of the light emission properties for silicon doped by RE is mainly limited to discussion of those for silicon doped by Er.Very few studies have been reported on luminescence properties for other RE doped silicon,many of them will be investigated in a deep going way.In this paper,rare earth ions Nd,Ce are implanted into monocrystal Si wafer and thermal oxide Si samples at the energy 45keV and with the doses of 1×1017,5×1017 and 1×1018cm-2 separately using metal vapor vacuum arc (MEVVA) ion implantation.After rapid annealing treatment to the above implanted samples at 900℃,1000℃ and 1100℃,the photoluminescence (PL) spectra excited by ultraviolet are measured by Hitachi F3010 photoluminescence spectrophotometer at room temperature.The results show that all the samples possess blue-violet photoluminescence properties under the ultraviolet light excitation and its light emission is stable.The photoluminescence efficiency for the samples varies with the anneal condition,and the light emission is more intense when the doped impurity concentration is greater within a certain limits.The feature and appearance of the samples was surveyed by use of atomic force microscopy (AFM).The experimental results show that the surface grain size and coarse degree for sample have influence on its light emission efficiency.The light emission efficiency is higher when the surface grain size is symmetrical and average coarse degree is little for samples.Besides,the Rutherford Backscattering Spectrum (RBS) at room temperature for the samples annealed under O2 at different temperature was measured.The photoluminescence mechanism for our sample is also discussed.关键词：rare-earth doped;ion implantation;photoluminescence;SiO2 thin film;surface morphology74|64|1更新时间：2020-08-11
- 摘要：The sol-gel process,which is mainly based on an inorganic polymerization reaction,is a chemical synthesis method initially used for the preparation of inorganic materials such as glasses and ceramics.The mild characteristics offered by the sol-gel process allow the introduction of organic molecules inside an inorganic network.Inorganic and organic components can then be mixed at the nanometric scale,in virtually any ratio leading to so called hybrid organic inorganic nanocomposites.These hybrids are extremely versatile in their composition,processing and the related optical and mechanical properties.Sol-gel derived silica gel(aerosol or serogel) is of great importance based on its wide applications in optics,catalysts,sensors and solar energy collectors.Organic dyes and rare earth ions have been incorporated into the microporous silica gel,which is generally considered to possess an optically inert framework.However,the sol-gel derived silica gel is not optically inert,but optically active,i.e.,it shows lminescence usder UV excitation.Of particular interest and importance is that,a new class of stable and efficient white photoluminescent silicate materials has been obtained from an alkoxysilane and a carboxylic acid through sol-gel route.Other related report is the sol-gel derived undoped usea cross linked organic inorgels which display strong blue light emission.In this paper,undoped SiO2 xerogels were prepared by the sol-gel method under various preparation conditions and compositions by using tetracthoxysilane(TEOS)and (3-aminopropyl) triethoxysilane(APS),orgaic acid (CH3COOH)and in orgagic acids (HCl,HNO3,H2SO4) as the main precursor.Luminescence spectra were used to characterize the resulted SiO2 xerogels.Under the excitation of 365nm all the xerogels exhibit strong luminescence in the blue region,but the emission intensity and position depend on the starting precureor compositions to a large extent.Suitable amount of polyethylene glycol(PEG500 and PEG10000)in the SiO2 xerogels can enhance the emssion intensity.Additionally,the emission intensity of the hybrid xerogels in creases with heat treatment temperature in the range of ambient to 200℃,and vacuum condition is also able to enhance the emission intensity.关键词：photoluminescence;SiO2;sol-gel method76|71|3更新时间：2020-08-11
- 摘要：Amorphous and nanocrystalline ZrO2 and ZrO2:Y(7%mol) were prepared by coprecipitated method,and their photoluminescence properties,sintering temperature and atmosphere dependence have been studied.The samples sintered at 300℃ had amorphous phase.At 900℃,they were crystallized into monoclinic phase and tetragonal phase for ZrO2 and ZrO2:Y(7%mol) respectively.Luminescence intensity was influenced by the concentration of oxygen vacancies and grain size.Amorphous samples had stronger intensity than nanocrystalline samples.The emission spectra had an obviously broad band compared to that of single crystal sample and were not sensitivity to the phase of samples.They can be decomposed of a Gaussian band (2.69eV) and an asymmetry band (3.12eV).The intensity of asymmetry band decreased more than that of Gaussian band with increasing sintering temperature.The intensities of two bands of the sample prepared in reductive atmosphere were stronger than that of the sample prepared in oxidative atmosphere.Two kinds of color center F+center and (F-F)+center have been proposed as the emission center for the Gaussian band and the asymmetric band.关键词：ZrO2;luminescence;nanocrystalline;amorphous89|74|4更新时间：2020-08-11
- 摘要：Nanocrystals ZnO are prepared by chemical precipitation.Crystal structure and ceramoc microstructure of powder samples are examined by XRD and TEM.The mean grain size of the materials was-calculated by Debye Scherrer method.The dependence of the mean grain size on reaction concentration is discussed.The results indicate that well-crystallized nano-ZnO is obtained with annealing temperature at 350℃.There exists a critical concentration which makes the size of nano-ZnO smallest.The other purpose of the present paper is to study the luminescence properties of the obtained sample.In particular the mechanism behind the visible luminescence has also been discussed in this paper.It should be said that the mechanism behind the visible luminescence is still a question of debate.Some authors attributed oxygen vacancies to the recombination centers.Other workers hypothesized that Zn vacancies were the centers responsible for green luminescence.The results obtained in the present paper support the point of view that Zn vacancies were the centers responsible for green luminescence and show that two phonon is involved in the emission processes.关键词：nano-ZnO powder;precipitation method;luminescence;quantum confinement effect87|84|12更新时间：2020-08-11
- 摘要：Violet light-emitting diodes chip (GaN-based) was used as primary light source and BaMg2Al16O27:Eu2+,Mn2+phosphors was used as light conversion materials.The EL spectral peak of violet LED chip is 395nm.The exciting spectra peak of BaMg2Al16O27:Eu2+,Mn2+phosphors is at 340nm,but the exciting intensity at 388nm is about the 58% of the maxmum exciting intensity at 340nm (peak).The PL spectrum peak of the BaMg2Al16O27:Eu2+,Mn2+phosphors is at 520nm and the FWHM is about 30nm.The PL spectra of BaMg2Al16O27:Eu2+,Mn2+phosphors is similar with that of green LED.The pure green light emitting diodes was fabricated by the way of phosphors conversion.The EL spectra peak of green LED is at 520 and the FWHM is about 30nm.The luminescent intensity is about 600mcd.关键词：phosphors;pure green LED;violet LE96|76|1更新时间：2020-08-11
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