The growth of LaBrs：Ce^3＋ crystal by the vertical Bridgman process in a nonvacuum atmosphere was reported. According to the dehydration procedure of LaBr3·7H2O and CeBr3·7H2O investigated by differential t...The growth of LaBrs：Ce^3＋ crystal by the vertical Bridgman process in a nonvacuum atmosphere was reported. According to the dehydration procedure of LaBr3·7H2O and CeBr3·7H2O investigated by differential thermal analysis/thermogravimetry （DTA/TG）, anhydrous LaBr3 and CeBr3 were prepared by heating LaBr3·7H2O and CeBr3·7H2O at 240-260℃ for 5-6 h in dried HBr atmosphere. Using the feed materials prepared from the anhydrous lanthanon bromides, a 0.5 mole fraction Ce^3＋ doped LaBr3 crystal with size ofФ25 mm×50 mm had been grown by vertical Bridgman process successfully. By sealing the feed material in a platinum crucible, the crystal could be grown in a nonvacuum atmosphere as the oxidization and volatilization of the melt could be avoided. The crystal was grown with the optimum conditions such as a growth rate of 0.5-1.0 mm/h and a temperature gradient of around 30℃/cm across solid-liquid interface under a furnace temperature of 850-880℃. The crystal was characterized by DTA/TG, X-ray diffraction （XRD）, optical transmission, photoluminescence and X-ray stimulated luminescence measurement. The Bridgman process was confirmed to be promising for growing transparent LaBr3：Ce^3＋ crystal with high optical quality.展开更多
Zr58.5Ti14.3Nb5.2Cu6.1Ni4.9Be11.0 bulk metallic glass matrix composites,containingβ-Zr dendrites,were fabricated by Bridgman solidification at the withdrawal velocity of 1.0 mm/s through a temperature gradient of～45...Zr58.5Ti14.3Nb5.2Cu6.1Ni4.9Be11.0 bulk metallic glass matrix composites,containingβ-Zr dendrites,were fabricated by Bridgman solidification at the withdrawal velocity of 1.0 mm/s through a temperature gradient of～45 K/mm.Subjected to the increasing compressive strain rates,the monotonic increasing and decreasing were obtained for the maximum strength and the fracture strain,respectively.The results show that high strain rate may induce the insufficient time for the interaction between shear bands and the crystalline phase,and early fracture occurs as a result.The fractographs are consistent with the mechanical properties,and the failure mode of the present Zr-based composites is in agreement with the frame of the ellipse criterion.展开更多
The paper reports that the shear-band spacing can be controlled by the Bridgman solidification technique for a model alloy of Zr38.3Ti32.9Nb7.3Cu6.2Be15.3.The volume percent of the glass phase is almost independent of...The paper reports that the shear-band spacing can be controlled by the Bridgman solidification technique for a model alloy of Zr38.3Ti32.9Nb7.3Cu6.2Be15.3.The volume percent of the glass phase is almost independent of the withdrawal velocity.The shear-band spacing reaches a minimum of about 3 μm with withdrawal velocity of 0.8 mm/s.The optimized mechanical properties,such as the fracture strength of ～2100 MPa and plastic strain of ～19%,have been obtained.The large plastic deformation is due to the dislocation slips in the dendrite phase and shear-band propagations in the glass phase.展开更多
Alternating current poling(ACP)in air by changing poling temperature(70e130℃)and voltages(2e6 kVrms/cm)on pseudo-ternary 0.24 Pb(In_(1/2)Nb_(1/2))O_(3)-0.46 Pb(Mg1/3Nb_(2/3))O3-0.30PbTiO_(3)(PIMN-0.30PT)single crysta...Alternating current poling(ACP)in air by changing poling temperature(70e130℃)and voltages(2e6 kVrms/cm)on pseudo-ternary 0.24 Pb(In_(1/2)Nb_(1/2))O_(3)-0.46 Pb(Mg1/3Nb_(2/3))O3-0.30PbTiO_(3)(PIMN-0.30PT)single crystals(SCs)manufactured by continuous-feeding Bridgman(CF BM)method was investigated.Free dielectric permittivity(εT 33/ε0)and piezoelectric constant(d33)were improved to be 7000 and 2340 pC/N,which were 29%higher than those of direct current poling(DCP)at 90℃ with 4 kV/cm(εT 33/ε0=5440,d_(33)=1810 pC/N).However,phase change temperature(Tpc)decreased from 94℃ to 78℃ as opposite results reported by other groups.We demonstrated that the high temperature(HT)ACP improved piezoelectric performance of CF BM SCs,however,the Tpc were different from other crystal growth method.The well-designed ACP process was a promising method for mass production not only to enhance the electrical properties for the pseudo-ternary SCs but also reduce the risk of breakdown and realizes organic solvent-free poling process.展开更多
The growth of CdZnTe crystals with diameter up to 60 mm using bottom-seeded Bridgman method as well as Bridgman accelerated crucible rotation technique (ACRT-B) was investigated. Both ingots exhibit high yields, where...The growth of CdZnTe crystals with diameter up to 60 mm using bottom-seeded Bridgman method as well as Bridgman accelerated crucible rotation technique (ACRT-B) was investigated. Both ingots exhibit high yields, where single crystal with the volume exceeding 200 cm3 is produced. The crystal properties of two ingots were compared in the aspects of yields, crystalline quality and composition uniformity. For CdZnTe ingot grown by bottom-seeded Bridgman method, the full width at half-maximum (FWHM) of X-ray rocking curve was determined to be 36″, indicating a better crystalline quality than ingot grown by ACRT-B method, which gave FWHM of 56″. The composition distribution of Zn and In in CdZnTe was determined by using electron probe microanalysis (EPMA) and inductively coupled plasma mass spectrometry (ICP-MS), respectively. The effective segregation coefficients of Zn kZn and In kIn in the two ingots were evaluated by fitting the experimental data with the Pfann equation.展开更多
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...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.展开更多
The effects of pulling velocity on the solidification behavior and microstructural parameters of A1Sil0Mg alloys prepared in a Bridgman-type directional solidification furnace were investigated. The microstructure, pa...The effects of pulling velocity on the solidification behavior and microstructural parameters of A1Sil0Mg alloys prepared in a Bridgman-type directional solidification furnace were investigated. The microstructure, particularly the secondary dendritic arm spacing （SDAS）, and the Brinell hardness （BH） of the solidified A1Sil0Mg alloys were characterized for samples with cylindrical shapes and differ- ent conicities （θ = 0°, 5°, and 10°）. Microstructural studies revealed an increased density of ct-A1 phase dendrites and a decreased interden- dritic distance with increasing pulling velocity. The dendrites were found to be preferentially oriented along the pulling direction for low pulling velocities. For larger pulling velocities, the dendrites grew first in the cooling direction but then broke as others nucleated and coars- ened. The HB values of the solidified samples increased as the pulling velocity increased. In regard to sample conicity, smaller dendrites were observed for an apex angle of θ = 5°, resulting in the largest HB value. This result was interpreted in terms of the favorable orientation of the dendrite along the pulling direction.展开更多
A Galerkin finite element method, together with the boundary conformal mapping technique, is used to investigate the change of melWcrystal interface under low gravity during the growth of LEAF system. Results have sho...A Galerkin finite element method, together with the boundary conformal mapping technique, is used to investigate the change of melWcrystal interface under low gravity during the growth of LEAF system. Results have shown that strong convection can cause a deeply concave interface toward the crystal, and significantly increase radial thermal gradients near the interface. The flow intensity and the change of the gravity have a linear relationship under low gravity (g o u = 10?2-10?6). At smallMa number, the maximum acceleration for keeping a planar growth interface is gmax = 1 × 10?3 g under our given conditions. In addition, the growth velocity may have some influence on the growth interface shape even atpg gravity level, indicating that the growth velocity cannot be too fast even when convection is very weak.展开更多
Directional solidification experiments on Pb-Bi peritectic alloys were carried out at very low growth rate （v=0.5 μm/s） and high temperature gradient （G=35 K/mm） in an improved Bridgman furnace. The banding struc...Directional solidification experiments on Pb-Bi peritectic alloys were carried out at very low growth rate （v=0.5 μm/s） and high temperature gradient （G=35 K/mm） in an improved Bridgman furnace. The banding structures were observed in both hypoperitectic and hyperperitectic compositions （Pb-xBi, x=26%, 28%, 30% and 34%）. Tree-like primary α phase in the center of the sample surrounded by the peritectic β phase matrix was also observed, resulting from the melt convection. The banding microstructure, however, is found to be transient after the tree-like structure and only the peritectic phase forms after a few bands. Composition variations in the banding structure are measured to determine the nucleation undercooling for both α and β phases. In a finite length sample, convection is shown to lead only to the transient formation of bands. In this transient banding regime, only a few bands with a variable width are formed, and this transient banding process can occur over a wide range of compositions inside the two-phase peritectic region.展开更多
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 a...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.展开更多
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 ...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.展开更多
Large size,high-density(99.97%)and well-organized Al2O3/Y3Al5O12(YAG)eutectic ceramics were prepared by the modified Bridgman method.The evolution of the three dimensional microstructure and micropores were investigat...Large size,high-density(99.97%)and well-organized Al2O3/Y3Al5O12(YAG)eutectic ceramics were prepared by the modified Bridgman method.The evolution of the three dimensional microstructure and micropores were investigated.The diameter of the micro-pores and the porosity decreased during directional solidification.The average equivalent diam eter of the micro-pores was 2.41μm in the well-prepared eutectic ceramics.Most of the pores(98.07%)were smaller than 4μm.These data are comparable to those prepared by the optical floating zone method.The as-grown eutectic ceramics were polycrystalline,but the interfaces were well-bonded and there were no amorphous phases in the microstructure.The misfits of the different crystallographic relationships were calculated,and the bottleneck of the single-crystal preparation was identified.These results could provide theoretical guidance for the preparation of large,single-crystal Al2O3/YAG eutectic ceramics by the modified Bridgman method.展开更多
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 conc...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.展开更多
A Ce^（3＋）tion-doped α-Na YF_4 single crystal of high quality is grown successfully by an improved flux Bridgman method under the conditions of taking the chemical raw composition of Na F：KF：YF_3：CeF_3 in the mo...A Ce^（3＋）tion-doped α-Na YF_4 single crystal of high quality is grown successfully by an improved flux Bridgman method under the conditions of taking the chemical raw composition of Na F：KF：YF_3：CeF_3 in the molar ratio of30∶18∶48∶4, where the KF is shown to be an effective assistant flux. The x ray diffraction, absorption spectra,excitation spectra, and emission spectra of the Ce^（3＋）t-doped α-Na YF_4 single crystal are measured to investigate the phase and optical properties of the single crystals. The absorption spectrum of the Ce^（3＋）t：α-Na YF_4 shows a strong band that peaks at the wavelength of 300 nm. The emission spectrum of the Ce^（3＋）t：α-Na YF_4 emits an intense ultraviolet（UV） band at the wavelength of 332 nm under the excitation of 300 nm light. Two separated luminous bands of 330 and 350 nm, which correspond to the transitions 5d → 2F25∕2and 5d → F7∕2, can be obtained by Gauss fitting. The strong emission intensity at the UV band and the excellent optical transmission in the range of UV wavelengths indicate that Ce^（3＋）t：α-Na YF_4 single crystals can be considered as a promising material for UV lasers.展开更多
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 see...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.展开更多
基金supported by the Scientific & Techni-cal Project of Zhejiang Province, China (No 2005C31029)the Doctor Science Foundation of Ningbo City, China(No 2005A610021)
文摘The growth of LaBrs：Ce^3＋ crystal by the vertical Bridgman process in a nonvacuum atmosphere was reported. According to the dehydration procedure of LaBr3·7H2O and CeBr3·7H2O investigated by differential thermal analysis/thermogravimetry （DTA/TG）, anhydrous LaBr3 and CeBr3 were prepared by heating LaBr3·7H2O and CeBr3·7H2O at 240-260℃ for 5-6 h in dried HBr atmosphere. Using the feed materials prepared from the anhydrous lanthanon bromides, a 0.5 mole fraction Ce^3＋ doped LaBr3 crystal with size ofФ25 mm×50 mm had been grown by vertical Bridgman process successfully. By sealing the feed material in a platinum crucible, the crystal could be grown in a nonvacuum atmosphere as the oxidization and volatilization of the melt could be avoided. The crystal was grown with the optimum conditions such as a growth rate of 0.5-1.0 mm/h and a temperature gradient of around 30℃/cm across solid-liquid interface under a furnace temperature of 850-880℃. The crystal was characterized by DTA/TG, X-ray diffraction （XRD）, optical transmission, photoluminescence and X-ray stimulated luminescence measurement. The Bridgman process was confirmed to be promising for growing transparent LaBr3：Ce^3＋ crystal with high optical quality.
基金supported by the New Century Excellent Talents in Universities(No.NCET-05-0105)the National Basic Research Priorities Program of China(No.2007CB613903)
文摘Zr58.5Ti14.3Nb5.2Cu6.1Ni4.9Be11.0 bulk metallic glass matrix composites,containingβ-Zr dendrites,were fabricated by Bridgman solidification at the withdrawal velocity of 1.0 mm/s through a temperature gradient of～45 K/mm.Subjected to the increasing compressive strain rates,the monotonic increasing and decreasing were obtained for the maximum strength and the fracture strain,respectively.The results show that high strain rate may induce the insufficient time for the interaction between shear bands and the crystalline phase,and early fracture occurs as a result.The fractographs are consistent with the mechanical properties,and the failure mode of the present Zr-based composites is in agreement with the frame of the ellipse criterion.
文摘The paper reports that the shear-band spacing can be controlled by the Bridgman solidification technique for a model alloy of Zr38.3Ti32.9Nb7.3Cu6.2Be15.3.The volume percent of the glass phase is almost independent of the withdrawal velocity.The shear-band spacing reaches a minimum of about 3 μm with withdrawal velocity of 0.8 mm/s.The optimized mechanical properties,such as the fracture strength of ～2100 MPa and plastic strain of ～19%,have been obtained.The large plastic deformation is due to the dislocation slips in the dendrite phase and shear-band propagations in the glass phase.
文摘Alternating current poling(ACP)in air by changing poling temperature(70e130℃)and voltages(2e6 kVrms/cm)on pseudo-ternary 0.24 Pb(In_(1/2)Nb_(1/2))O_(3)-0.46 Pb(Mg1/3Nb_(2/3))O3-0.30PbTiO_(3)(PIMN-0.30PT)single crystals(SCs)manufactured by continuous-feeding Bridgman(CF BM)method was investigated.Free dielectric permittivity(εT 33/ε0)and piezoelectric constant(d33)were improved to be 7000 and 2340 pC/N,which were 29%higher than those of direct current poling(DCP)at 90℃ with 4 kV/cm(εT 33/ε0=5440,d_(33)=1810 pC/N).However,phase change temperature(Tpc)decreased from 94℃ to 78℃ as opposite results reported by other groups.We demonstrated that the high temperature(HT)ACP improved piezoelectric performance of CF BM SCs,however,the Tpc were different from other crystal growth method.The well-designed ACP process was a promising method for mass production not only to enhance the electrical properties for the pseudo-ternary SCs but also reduce the risk of breakdown and realizes organic solvent-free poling process.
基金Project(50772091) supported by the National Natural Science Foundation of ChinaProject(2008044185) supported by China Postdoctoral Science Foundation
文摘The growth of CdZnTe crystals with diameter up to 60 mm using bottom-seeded Bridgman method as well as Bridgman accelerated crucible rotation technique (ACRT-B) was investigated. Both ingots exhibit high yields, where single crystal with the volume exceeding 200 cm3 is produced. The crystal properties of two ingots were compared in the aspects of yields, crystalline quality and composition uniformity. For CdZnTe ingot grown by bottom-seeded Bridgman method, the full width at half-maximum (FWHM) of X-ray rocking curve was determined to be 36″, indicating a better crystalline quality than ingot grown by ACRT-B method, which gave FWHM of 56″. The composition distribution of Zn and In in CdZnTe was determined by using electron probe microanalysis (EPMA) and inductively coupled plasma mass spectrometry (ICP-MS), respectively. The effective segregation coefficients of Zn kZn and In kIn in the two ingots were evaluated by fitting the experimental data with the Pfann equation.
基金financially supported by the Natural Science Foundation of Shanghai(Nos.19ZR1419900,19ZR1420100)Shanghai Engineering Research Center of Hot Manufacturing(No.18DZ2253400)。
文摘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.
基金financially supported by the doctoral scholarship grant of the Algerian-MHESR
文摘The effects of pulling velocity on the solidification behavior and microstructural parameters of A1Sil0Mg alloys prepared in a Bridgman-type directional solidification furnace were investigated. The microstructure, particularly the secondary dendritic arm spacing （SDAS）, and the Brinell hardness （BH） of the solidified A1Sil0Mg alloys were characterized for samples with cylindrical shapes and differ- ent conicities （θ = 0°, 5°, and 10°）. Microstructural studies revealed an increased density of ct-A1 phase dendrites and a decreased interden- dritic distance with increasing pulling velocity. The dendrites were found to be preferentially oriented along the pulling direction for low pulling velocities. For larger pulling velocities, the dendrites grew first in the cooling direction but then broke as others nucleated and coars- ened. The HB values of the solidified samples increased as the pulling velocity increased. In regard to sample conicity, smaller dendrites were observed for an apex angle of θ = 5°, resulting in the largest HB value. This result was interpreted in terms of the favorable orientation of the dendrite along the pulling direction.
文摘A Galerkin finite element method, together with the boundary conformal mapping technique, is used to investigate the change of melWcrystal interface under low gravity during the growth of LEAF system. Results have shown that strong convection can cause a deeply concave interface toward the crystal, and significantly increase radial thermal gradients near the interface. The flow intensity and the change of the gravity have a linear relationship under low gravity (g o u = 10?2-10?6). At smallMa number, the maximum acceleration for keeping a planar growth interface is gmax = 1 × 10?3 g under our given conditions. In addition, the growth velocity may have some influence on the growth interface shape even atpg gravity level, indicating that the growth velocity cannot be too fast even when convection is very weak.
基金Project (20110491492) supported by the China Postdoctoral Science FoundationProject (20114BAB216017) supported by the Natural Science Foundation of Jiangxi Province, ChinaProject (GJJ12035) supported by the Science Foundation of the Educational Department of Jiangxi Province, China
文摘Directional solidification experiments on Pb-Bi peritectic alloys were carried out at very low growth rate （v=0.5 μm/s） and high temperature gradient （G=35 K/mm） in an improved Bridgman furnace. The banding structures were observed in both hypoperitectic and hyperperitectic compositions （Pb-xBi, x=26%, 28%, 30% and 34%）. Tree-like primary α phase in the center of the sample surrounded by the peritectic β phase matrix was also observed, resulting from the melt convection. The banding microstructure, however, is found to be transient after the tree-like structure and only the peritectic phase forms after a few bands. Composition variations in the banding structure are measured to determine the nucleation undercooling for both α and β phases. In a finite length sample, convection is shown to lead only to the transient formation of bands. In this transient banding regime, only a few bands with a variable width are formed, and this transient banding process can occur over a wide range of compositions inside the two-phase peritectic region.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 50972061,51272109,and 21171102)the Natural Science Foundation of Zhejiang Province of China (Grant Nos. R4100364 and Z4110072)+1 种基金the Natural Science Foundation of Ningbo City (Grant No. 2012A610115)K. C.Wong Magna Fund in Ningbo University
文摘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.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60938001,60908030,61178056 and 51002175)the Hundred Talent Project of the Chinese Academy of Sciences
文摘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.
基金financially supported by the National Natural Science Foundation of China (Nos. 51804252 and 51701156)the Equipment Pre-Research Foundation of China (Nos. 6140759040102 and 6140923040203)the Doctoral Starting Fund of Xi’an University of Technology (No. 101-451116013)
文摘Large size,high-density(99.97%)and well-organized Al2O3/Y3Al5O12(YAG)eutectic ceramics were prepared by the modified Bridgman method.The evolution of the three dimensional microstructure and micropores were investigated.The diameter of the micro-pores and the porosity decreased during directional solidification.The average equivalent diam eter of the micro-pores was 2.41μm in the well-prepared eutectic ceramics.Most of the pores(98.07%)were smaller than 4μm.These data are comparable to those prepared by the optical floating zone method.The as-grown eutectic ceramics were polycrystalline,but the interfaces were well-bonded and there were no amorphous phases in the microstructure.The misfits of the different crystallographic relationships were calculated,and the bottleneck of the single-crystal preparation was identified.These results could provide theoretical guidance for the preparation of large,single-crystal Al2O3/YAG eutectic ceramics by the modified Bridgman method.
基金Project supported by the National Natural Science Foundation of China(51772159)the Natural Science Foundation of Zhejiang Province(LZ17E020001)The authors would like to acknowledge program of the K.C.Wong Magna Fund in Ningbo University.
文摘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.
基金supported by the National Natural Science Foundation of China(Nos.51472125 and51272109)the K.C.Wong Magna Fund of Ningbo University
文摘A Ce^（3＋）tion-doped α-Na YF_4 single crystal of high quality is grown successfully by an improved flux Bridgman method under the conditions of taking the chemical raw composition of Na F：KF：YF_3：CeF_3 in the molar ratio of30∶18∶48∶4, where the KF is shown to be an effective assistant flux. The x ray diffraction, absorption spectra,excitation spectra, and emission spectra of the Ce^（3＋）t-doped α-Na YF_4 single crystal are measured to investigate the phase and optical properties of the single crystals. The absorption spectrum of the Ce^（3＋）t：α-Na YF_4 shows a strong band that peaks at the wavelength of 300 nm. The emission spectrum of the Ce^（3＋）t：α-Na YF_4 emits an intense ultraviolet（UV） band at the wavelength of 332 nm under the excitation of 300 nm light. Two separated luminous bands of 330 and 350 nm, which correspond to the transitions 5d → 2F25∕2and 5d → F7∕2, can be obtained by Gauss fitting. The strong emission intensity at the UV band and the excellent optical transmission in the range of UV wavelengths indicate that Ce^（3＋）t：α-Na YF_4 single crystals can be considered as a promising material for UV lasers.
文摘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.
