GdCa_4O(BO_3)_3晶体的Bridgman法生长条件探索

Inorganic nonlinear optical crystal GdGa 4O(BO 3) 3(GdCOB) possesses moderate NLO efficient (1.3pm/V) ,high damage threshold(>1GW/cm 2),and wide transmission wave band(320-2700nm).In addition,it is chemically stable,nonhygroscopic and easy to process,which makes GdCOB a promising practical NLO material for frequency conversion.Crack free single crystals of GdCOB with large size have been grown using the vertical Bridgman method for the first time.Stoichiometric amounts of starting materials 4N pure Gd 3O 3,H 3BO 3(or B 3O 3)and 3N pure CaCO 3 were mixed and preheated at 1100℃,then encapsulated in a Pt crucible with a single crystal seed.Thickness of the crucible we chose was within the range of 0.1—0.6mm.After thorough melting of the raw materials and partial melting of the seed(obtained by spontaneous nucleation),the crucible descended at a rate of <0.8mm/h.The vertical temperature gradient at the growth interface in the BR furnace was about 30—40℃/cm,and the temperature profile was kept symmetrical.Typical size of the GdCOB crystal without macroscopic defects obtained in this way was 25mm in diameter and 60mm in length.Due to the small temperature gradient in growth and the cooling process similar to the anneal after growth,cracking problem which was often met in pulling techniques was overcome efficiently.

Fluorescence properties of divalent and trivalent europium ions in CdWO_4 single crystals grown by the Bridgman method

Optical absorption,excitation,and fluorescence were investigated in Eu ion-doped CdWO4 single crystal grown by a modified Bridgman method.The results indicate that Eu^2＋ and Eu^3＋ ions coexist in CdWO4 crystal and an energy transfer occurs between these Eu^2＋ and Eu^3＋ ions.When the crystal is excited by 266-nm light,the energy corresponding to the 4f65d to 8S7/2 transition of Eu^2＋ ions results in the excitation of the Eu^3＋ ions to the 5DJ level.The effect on fluorescence of annealing in oxygen at various temperatures was investigated.The excitation intensity of Eu^2＋ ions at 266 nm decreases as annealing temperature increases from 300 K to 1073 K,but it remains at a certain equilibrium level when the annealing temperature is further increased.

Growth and Optical Spectra of Zn∶Er∶LiNbO_3 Crystals by Bridgman Method

The growth of LiNbO3 single crystal with Er^3＋/Zn^2＋ co-doped by the bridgman method and the characteristics of absorption spectra and fluorescence spectra were reported. By means of the optimized con- ditions such as growth rate of 0.8 - 1.5 mm · h^- 1, temperature gradient about 30 - 35℃ ·cm^-1 across the solid-liquid interface and sealed platinum, large size crystals containing Zn^2＋ （3%） and Er^3＋ （0.6%） with good optical quality were obtained. X-ray diffraction and DTA were used to characterize the crystals. The results indicate that the concentration of Er^3＋ ions in crystals decrease along the growth direction, the absorption intensity and the fluorescence intensity ions also decrease along the growth direction. of Er^3＋ However, for the upper part crystal, the upconversion fluorescence intensity is higher than that of the lower part crystal excited with 800 or 970 nm pump. The effects of crystal lattice, structure defect and effective segregation of Er^3＋ ions were discussed in respect to the variations were discussed of upconversion fluorescence intensity.

Vertical Bridgman Seeded Growth of Cd_(1-x)Zn_xTe Crystals

The method of vertical Bridgman seeded growth of Cdi.Zn.Te crystals was studied. This method ispromising in obtaining large size single crystals and improving the crystal structure. However, some prob-lems such as seeded growth failurc exist at present.(111)-oriented Cd_(0.96)Zn_(0.04)Te single crystal substrateswith size greater than 15×15 mm￣2 arc obtained. The FWHM ranges from 18 to 66 arc.sec and theresistivity is greater than 10￣6 obmem.

热电材料的研究及进展

In 1823,Thomas Seebeck first discovered the thermoelectric effect.A temperature difference across any electric conductor junction will generate a corresponding voltage difference.Probably the most familiar use of this so called Seebeck effect is thermocouple.When an electric current passing through junction which is composed of two dissimilar conductors results in the absorption or release of the heat,this is the Peltier effect.This effect makes thermoelectric refrigerator or heating devices possible.Moreover a power generator can be also invented from the application of thermoelectric materials.Thermoelectric materials are those which possess high thermoelectric figure of merit.The major problem for thermoelectric materials is poor efficiency.They are now used only in the fields in which cost is not a big problem such as space and some other instruments.Thermoelectric materials are not widely used nowadays.

YCOB晶体的坩埚下降法生长条件研究

Ca 4YO(BO 3) 3(YCOB) which possesses good NLO properties and chemical stability,is an excellent candidate for frequency conversion crystals to produce green and blue light (SHG and THG of Nd∶YAG laser).In this paper,preparation of the feed material and the vertical Bridgman growth condition for YCOB crystal is reported for the first time to our knowledge. YCOB crystals have been grown from the feed materials composed of Y 2O 3(4N),CaCO 3/CaO (A.R.) and H 3BO 3/B 2O 3(4N)by vertical Bridgman method.Since Ca 4YO(BO 3) 3 melts congruently,the feed material should be prepared in the stoichiometric composition.The evaporation of B 2O 3 at high temperature and the hygroscopicity of CaO,B 2O 3 and Y 2O 3 were carefully considered.It was showed by experiments that the feed material prepared by directly and thoroughly mixing together stoichiometric amount of Y 2O 3,CaO and B 2O 3 is suitable for the Bridgman growth of YCOB crystal.The melting point of YCOB crystal is 1510℃,and Pt crucible less than 1.0mm thick was chosen.The temperature of the furnace was controlled from 1560℃ to 1650℃.Owing to the extremely high melting points of both Y 2O 3 and CaO,the feed material had been heated at the above temperature for more than 10 hours before growth so that it melts thoroughly.The growth rate of 0.2-0.6mm/h and the temperature gradient near the solid-liquid interface of 40-60°C/cm were chosen.The Crack free and transparent YCOB crystals with 25mm in diameter and 50mm long have been grown in near sealed Pt crucibles under the above growth condition,which suggests that the vertical Bridgman method is suitable for the growth of YCOB crystal.

熔体生长中自然对流对溶质分凝和界面形状的影响

The uniformity of impurity distribution in a melt growth process is significantly determined by the melt convection and melt/crystal interface.Therefore,it is important to investigate the coupling effects of convection,segregation and growth interface shapes in order to largely improve the crystal quality. In this paper,we employ a finite element algorithm to study the vertical Bridgman growth process of Te doped GaSb crystals.The calculation model consists of unsteady state equations of heat transfer,mass transfer and momentum transfer,as well as their correspondingly boundary and initial conditions.A boundary conformal mapping technique is used to obtain the free melt/crystal interface shape and position which is a prior unknown.The set of algebraic equations obtained after finite element discretion is iteratively solved by Newton Raphson method until a given criterion is reached.

Growth and spectroscopic characteristics of Nd-doped PbWO_4 crystal

Nd-doped PbWO4 crystals are grown by using the modified Bridgman method.The spectroscopic properties of the crystals are investigated.The changes of the absorption band at 350 nm are discussed for samples annealed at 740℃ and 1040℃.The radiative lifetime of the 4 F 3/2 level is calculated by using the Judd-Ofelt theory according to the absorption spectrum of 0.5 at.% Nd-doped PbWO 4 crystal.The spontaneous Raman scattering properties of the crystals are analysed.

Parameter Optimization of CdZnTe Crystal Growth Simulated by Finite Element Method

During the crystal grown by VBM, the solid/liquid interface configurations greatly influence the quality of as-grown crystals. In this paper, finite element method (FEM) was used to simulate the growth process of CdZnTe crystal. The effects of different crucible moving rates and temperature gradient of adiabatic zone on crystal growth rate and solid-liquid interface configuration were studied as well. Simulation results show that when crucible moves at the rate of about 1mm/h, which is nearly equal to crystal growth rate, nearly flat solid/liquid interface and little variation of axial temperature gradient near it can be attained, which are well consistent with the results of experiments. CdZnTe crystal with low dislocation density can be obtained by employing appropriate crucible moving rate during the crystal growth process.

弛豫铁电单晶PMNT的生长及压电性能

It is difficult for the growth of relaxor ferroelectric single crystal (1 x ) Pb(Mg 1/3 Nb 2/3 )O 3 x PbTiO 3 (abbreviated as PMNT).The first reason is that there are four oxides as raw materials which are easily result in the nonstoichiometry and inhomogeneity for the single crystals,the second is that the pyrochlore phases appear easily for general growth condition that will reduce the dielectric and piezoelectric performance of PMNT single crystals,and the third is that the platinum crucible is easily leaked at the melting temperature of PMNT.A feasible technique has been used for the growth of PMNT single crystals after we researched the stability,structure and relation of PMN PT phases at high temperature.Now we can fabricate the large size and high quality of PMNT single crystals by a modified Bridgman technique.

坩埚下降法生长BSO(Bi_4Si_3O_(12))闪烁晶体

While the light output of BSO crystals is only 20% of the output of currently used BGO(Bi 4Ge 3O 12 )scintillation crystals,the decay time is one third(100ns).It is considered as promising for application as radiation detectors for high energy physics experiments.Based on this advantage,we have been proceeding with our development of large crystals to use practically.In this paper,we will review our results of crystal growth of BSO by Bridgman method and characterization on its scintillation performance. High purity raw materials of Bi 2O 3 and SiO 2 were mixed together,fired at 850℃,re mixed and sintered at 950℃.The charge was then fed into a Pt crucible of 25mm in diameter.For crystal growth,the crucible was lowered at 0.5mm/h in a furnace temperature gradient of about 10℃/cm.

Growth and characterization of ZnTe single crystal via a novel Te flux vertical Bridgman method

In this work,an Ⅱ-Ⅵ group semiconductor zinc telluride(ZnTe) single crystal is prepared by a novel vertical Bridgman method using Te as flux.The initial mole ratio of Zn/Te=3:7 is designed for raw material synthesis.ZnTe polycrystalline combined with rich Te is effectively fabricated through rocking technique at 1100℃.A Φ 25 mm × 65 mm ZnTe boule is successfully grown under a~40 ℃·cm^(-1) temperature gradient with a growth speed of 5 mm·day^(-1).The as-grown ZnTe crystal has a standard 1:1 stoichiometric ratio and pure F43 m phase structure.The maximum transmittance perpendicular to(110) plane is about 64%,and the band gap(E_(g)) is tested to be 2.225 eV.Terahertz(THz) examination results demonstrate that the time of the highest THz signal is around 17 ps and the frequency of the highest THz transmission is about 0.78 THz,implying that the ZnTe crystal grown by the present Te flux vertical Bridgman method has a good feasibility for THz application.

Photoluminescence properties of Tm^(3+)/Tb^(3+)/Sm^(3+) tri-doped Na_(5)Y_(9)F_(32) single crystal with high thermal stability for white light-emitting diodes

A novel Tm^(3+)/Tb^(3+)/Sm^(3+)tri-doped Na_(5)Y_(9)F_(32)single crystal was synthesized by a modified Bridgman method for the propose of white light emitting diodes.The fluorescence spectra of various Sm^(3+)ion concentrations and fixed 0.4 mol%Tm^(3+)and 0.5 mol%Tb^(3+)were measured and studied systematically excited by near-ultraviolet light of 355 nm.The Sm3+ion concentration takes apparent effect on the relative intensity of peaks in the visible region and the color coordinate combining from these emission bands.A near pure white light emission with color coordinates(0.3295,0.3057)and color temperature(5657 K)can be obtained when the concentrations of Tm^(3+),Tb^(3+)and Sm^(3+)ions are 0.4 mol%,0.5 mol%and 0.8 mol%,respectively.Furthermore,the practical down-conversion internal quantum yield was measured by integrating spheres at about 14.39%.The tri-doped Na_(5)Y_(9)F_(32)single crystal shows a high thermal stability inferring from the temperature dependent emission in which the integrated emission intensities are reduced only by^3%with the increase of temperature from 280 to 450 K.The present results demonstrate that the Tm^(3+)/Tb^(3+)/Sm^(3+)tri-doped Na_(5)Y_(9)F_(32)single crystal may provide a promising candidate for white light-emitting diodes,luminescent materials and fluorescent display devices.

Growth,crystalline quality and transition variation of ternary Pb(In_(1/2)Nb_(1/2))O_(3)-Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3) ferroelectric crystals

Bulk crystals of high Curie temperature(T_(C))24Pb(In_(1/2(Nb_(1/2))O_(3)-43Pb(Mg_(1/3)Nb_(2/3))O_(3)-33PbTiO_(3)(24PIN-43PMN-33PT)with 55 mm in diameter and 130mm in length were reproducibly grown by the bottom-seeded Bridgman method.The X-ray diffraction(XRD)spectrum indicated that the as-grown crystal was a single phase with rthombohedral structure at room temperature,the domain morphology and the phase transition sequence of R→T→C were observed,the full width at half maximum(FWHM)of X-ray rocking curve of(002)face was about 0.77°,and the defect density was inferred to 2.56×10^(10)cm^(-2).The measured density of the as-grown crystals was very close to the theoretical one.Variation of the transition temperature of the as-grown crystals along the growth direction revealed that T_(C) increased linearly along the growth direction and rthombohedral to tetrahedral phase transition temperature(T_(RT))gradually decreased in the middle part of the ingot.

PIN–PMN–PT piezoelectric crystals with increased rhombohedral-to-tetragonal phase transition temperature

In this work,crystal growth and characterization of PIN–PMN–PT(29–59%PIN and 28–35%PT)were conducted to understand how PIN ratio in the PIN–PMN–PT system impacts its phase stability during crystallization.High-quality PIN–PMN–PT crystals with 36%PIN were obtained using the self-seeded Bridgman process,even though the cubic phase In_(2)O_(3) formed at the very beginning of solidification.The melt became more unstable when the PIN ratio in the PIN–PMN–PT system increased to 49%and above,which affected the composition and quality of the as-grown crystals significantly.By increasing the PIN to 36%in PIN–PMN–PT crystal,the rhombohedral-to-tetragonal phase transition temperatures and the coercive field reached 115–135℃ and 4.55.6 kV/cm,respectively,that greatly expanded the operation domains compared to PMN–PT crystals.