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.

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.

Microstructure evolution and crystallography of directionally solidified Al2O3/Y3Al5O12 eutectic ceramics prepared by the modified Bridgman method

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.

中长波Cr^(2+)/Fe^(2+)∶CdSe激光晶体生长及元件制备

本文采用自主研发的双温区真空石墨加热单晶炉,通过钼坩埚密封布里奇曼法成功生长出了Cr^(2+)∶CdSe晶体和Fe^(2+)∶CdSe晶体,晶体尺寸达Φ51 mm×110 mm。Cr^(2+)∶CdSe晶体和Fe^(2+)∶CdSe晶体分别在1400~2400 nm和2500~5200 nm波段存在明显的吸收,同时,Cr^(2+)∶CdSe晶体和Fe^(2+)∶CdSe晶体在7~15μm波段透过率均接近CdSe晶体透过极限(~70%),换算吸收系数约为0.005 cm^(-1)。采用钼坩埚密封布里奇曼法制备的Cr^(2+)/Fe^(2+)∶CdSe晶体具有过渡金属离子掺杂浓度可控、掺杂均匀、晶体品质高等优点,可同时作为中波红外激光晶体和长波红外非线性光学晶体材料。

CsPbBr_(3)晶体生长及变温霍尔效应研究

以定向凝固法提纯的CsPbBr_(3)多晶为原料,采用垂直布里奇曼法生长出尺寸为∅30 mm×70 mm的CsPbBr_(3)单晶。采用ICP-OES对提纯后的多晶测试表明,提纯后的CsPbBr_(3)多晶中杂质含量减少了28.7%。经XRD和EDS对切割得到的晶片分析发现,晶片的晶面方向属{210}晶面族,晶体中Cs、Pb、Br_(3)种元素分布均匀,原子百分含量符合化学计量比。采用傅里叶红外光谱仪和紫外-可见分光光度计对晶体的透过率测试显示,生长晶体在500~4000 cm^(-1)波数范围内的红外透过率超过75%,紫外短波截止边为552 nm,拟合计算出对应的禁带宽度为2.246 eV。选取7个不同温度点对CsPbBr_(3)单晶进行变温霍尔效应测试发现,生长晶体为P型导电,在250~300 K和300~350 K之间晶体中主要的载流子散射机制分别为声学波散射和电离杂质散射,在150~250 K温度范围内,更符合多种散射机构共同作用的散射机制。进一步拟合载流子浓度p与1/T的关系,计算获得晶体中杂质电离能ΔE_(A)=0.3042 eV。

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.

掺铈Cs_(2)BaBr_(4)晶体的生长和闪烁性能研究

以高纯度BaBr_(2)、CsBr、CeBr_(3)为原料,采用高温固相反应法合成了Cs_(2)BaBr_(4)∶1%Ce^(3+)多晶料,并通过坩埚下降法生长了Cs_(2)BaBr_(4)∶1%Ce^(3+)晶体。将晶体切割研磨抛光后得到不同厚度的Cs_(2)BaBr_(4)∶1%Ce^(3+)晶片。对晶体进行了物相分析,XRD图谱表明晶体为一致熔融物,且无相变。研究了晶体的闪烁性能,测试了光学透射率、光致发光、X射线激发发光、多通道gamma能谱、衰减时间。与LaBr_(3)晶体对比,分析了晶体的吸湿性。结果表明,晶体的光学透过率接近80%,在一定波段的紫外光及X射线的激发下,晶体在349与372 nm波长有发射峰。^(137)Cs源伽马射线的激发下,能量分辨率为11%,在紫外激发下,晶体衰减时间为21.9 ns。晶体的吸湿性比LaBr_(3)晶体有大幅改善。

铝掺杂对硒化铟晶体结构与性能的影响

硒化铟(InSe)是一种新型的窄禁带(1.3 eV)层状半导体,具有优异的塑性和电学性能,在新型电子和光电子器件中具有广泛应用前景。采用布里奇曼(Bridgman)法生长了未掺杂和铝掺杂的InSe晶体,通过能谱仪(EDS)和扫描电子显微镜(SEM)对制备材料的化学成分和表面形貌进行了表征。本文研究发现,铝掺杂可调节InSe晶体的塑性和光电性能。X射线衍射(XRD)分析表明晶体具有六方结构,结合拉曼光谱表征证实晶体结构为ε-InSe。纳米压痕测量表明,随着铝掺杂量的增加,InSe晶体的硬度和模量降低,材料的塑性提高。霍尔效应测量和光学吸收谱结果表明,铝掺杂可提升载流子浓度和禁带宽度。

垂直Bridgman生长CdTe过程的数值模拟

采用 Galerkin有限元算法 ,计算了垂直 Bridgman生长 Cd Te过程中的温场分布、液体流动和固液界面的形状 ,分析了生长速率、温区分布等参数对固液界面的影响 .计算结果表明 ,较小的生长速率可以获得更为平坦的固液界面 ,适当增加结晶区域的温度梯度也是改善固液界面形状的一个有效方法 .同时 ,通过对生长系统中的热流分析 ,表明在生长过程的中间阶段 ,热量交换主要集中在梯度区附近 。

自发成核Bridgman法生长LaBr_3∶Ce晶体

本文用垂直Bridgman自发成核的方法生长了尺寸达φ25mm×30mm的LaBr3∶Ce单晶,晶体透明,无宏观缺陷。分析了晶体生长中主要的问题,指出了原料处理的关键,并指出了自发成核条件下晶体最有可能的生长取向为[001]方向,该方向对抑制晶体开裂非常有利。

高光产额SrI_(2)Eu^(2+)晶体制备及其闪烁性能研究

SrI_(2)Eu^(2+)晶体因其极高的光产额和优良的能量分辨率,在伽马射线高分辨测量中呈现出良好的应用前景。采用改进的坩埚下降法制备出掺杂浓度为5.0%的SrI_(2)Eu^(2+)晶体,加工制成了直径为25 mm,厚度分别为3,6,9,12 mm的单透光防潮封装SrI_(2)Eu^(2+)闪烁体。研究了4种不同尺寸闪烁体对^(241)Am,^(137)Cs,^(60)Co放射源伽马射线的响应,测试了SrI_(2):Eu^(2+)晶体的荧光光谱、能量分辨率、发光产额及衰减时间等闪烁性能。实验结果表明:SrI_(2)Eu^(2+)晶体的发光光谱峰值位于436 nm,SrI_(2)Eu^(2+)晶体闪烁性能随晶体厚度减薄或伽马射线能量的提高而提升。3 mm厚度SrI_(2)Eu^(2+)闪烁体对1.173 MeV^(60)Co伽马射线的能量分辨率达到了2.74%,在^(137)Cs源伽马射线激发下,光产额达到1.23×10^(5)MeV^(-1),是传统NaI:Tl闪烁体光产额的3倍以上,与当前国际上报道的最好的实验结果相当。

Bridgman法生长的PWO晶体的发光特性和透光特性

本文采用改进的Bridgman法，以纯度不低于99．99％的PbO和WO3为原料，生长出无色透明的、大尺寸的PbWO4（PWO）晶体，研究了晶体沿生长方向不同部位的透射光谱及X射线激发的发射光谱特性．发现改进的Bridgman法生长的PWO晶体具有较好的发光均匀性和透光均匀性，其原因主要是改进的Bridgman法采用密封的坩埚，有效地抑制了组份（PbO和WO3）的挥发.

Cs_(4)EuI_(6)∶Sm近红外闪烁晶体的生长及发光性能研究

随着长波敏感硅基光电探测器的发展,近红外闪烁晶体逐渐成为研究热点,其中Sm^(2+)掺杂的Eu^(2+)基卤化物晶体表现出优异的近红外发光性能。本文利用布里奇曼法成功制备了尺寸达到厘米级别的Cs_(4)EuI_(6)∶Sm近红外闪烁晶体,通过XRD、XPS和ICP-OES等手段研究了晶体的组分和结构。结果表明,Sm^(2+)成功掺入Cs_(4)EuI_(6)基质,且对基质的晶体结构无明显影响。在紫外和X射线的激发下,晶体主要呈现两个发光中心(Eu^(2+)和Sm^(2+)),发光峰位于450和840 nm左右,分别对应于Eu^(2+)和Sm^(2+)的5d→4f的跃迁发光,紫外激发下的Eu^(2+)和Sm^(2+)的荧光衰减寿命均处于微秒级别。结果表明,随着Sm^(2+)掺杂浓度的增加,发光波长由蓝光逐渐变为近红外光。同时系统研究了不同Sm^(2+)浓度掺杂对晶体发光性能、Eu^(2+)-Sm^(2+)能量传递及荧光寿命的影响,实验结果表明,改变Sm^(2+)掺杂浓度可以调控晶体的发光性能。

Bridgman法晶体生长过程中界面形状的改变

对不同生长条件下,Bridgm an法晶体生长过程进行了计算,对界面形状的改变的规律加以总结,并讨论了不同生长条件对界面形状的改变的影响。换热系数、导热系数和晶体宽度是影响界面凸凹程度及其变化趋势的重要参数。

坩埚下降法生长2英寸镱掺杂钙铌镓石榴石单晶

本文通过坩埚下降法生长了直径2英寸(1英寸=2.54 cm)的4.2%镱离子掺杂钙铌镓石榴石(Yb∶Ca_(3)(NbGa)_(5)O_(12))晶体,获得的晶体外观完整,无明显瑕疵。通过XRD测试分析了晶体的结构,该晶体为立方晶系,晶胞参数a=b=c=12.493。将该晶体定向切割获得了10 mm×10 mm×1 mm的(420)面薄片,对薄片进行两面研磨抛光得到最终样品。通过X射线衍射、紫外可见光分光光度计、荧光光谱仪等对该样品进行性能表征,结果表明获得的晶体摇摆曲线半峰全宽为43″,在近红外波长范围内透过率达到了80%,在935 nm处吸收峰半峰全宽为47.15 nm,吸收截面达到了1.53×10^(-20)cm^(2),用980 nm激光器对该样品进行激发,在1031 nm处得到发射峰,对应Yb^(3+)由^(2)F_(5/2)激发态到^(2)F_(7/2)基态的跃迁。

用NH_4Cl-H_2O溶液共晶凝固实验模拟Bridgman法晶体生长过程

利用NH4Cl-H2O溶液的共晶凝固模拟Bridgman法晶体生长过程,通过粒子图像测速系统测量了矩形腔和圆柱腔内NH4Cl-H2O溶液共晶凝固过程中的流场,结合温度变化得到了凝固过程中流动和温度的耦合规律.实验结果表明:在侧壁和底部冷却条件下,两种腔室内溶液共晶凝固过程中流场的变化基本相似,形成竖壁面附近溶液向下流动、中心区域溶液向上流动的对流涡;凝固开始后,热交换和潜热的释放使液相区内温度下降趋于平缓;圆柱腔内出现了角区绕流和二次对流涡现象.实验得到的流动和温度变化规律为理论建模及数值计算提供了有用的实验数据.

在横向磁场中用Bridgman法生长HgCdTe晶体

在横向磁场中用 Ｂｒｉｄｇｍａｎ法生长的晶锭其轴向组分分布在中部和尾部具有相同的趋势，在头部有三种类型的分布磁场通过对固液混合区对流的作用影响溶质的再分布和轴向组分分布突然施加磁场和中断磁场都引起轴向组分分布的突变．当安瓿绕生长轴匀速旋转时、晶锭的径向组分分布既没有安瓿不旋转时的偏心特征，也没有常规 Ｂｒｉｄｇｍａｎ法生长晶体的径向对称性尾部呈现圆锥状的凸起。

四方品系晶体的Bridgman法生长的稳态数值模拟

本文对四方晶系晶体的Bridgman法生长进行了稳态数值模拟。当熔体的导热系数位于晶体横向导热系数和纵向导热系数中间的一小段时,将产生“W”形固液界面。通过比较,指出不同导热系数组合时晶体生长的难易。当熔体的导热系数位于晶体横向导热系数和纵向导热系数中间的一小段时,界面平坦,容易长出较好质量的晶体。对中、低级晶系的生长,晶体横向导热系数应大于纵向导热系数。

ACRT-Te溶液Bridgman法生长的In掺杂CdMnTe界面研究(英文)

采用ACRT-Te溶液垂直布里奇曼法成功制备出直径为30mm、长度为60mm的CdMnTe晶锭。相对于普通布里奇曼法生长的CdMnTe晶锭,Te溶液法生长的 CdMnTe晶锭中的孪晶大大减少。但是由于较高的Te夹杂相密度,红外透过成像显示晶锭生长界面的微观形貌既不均匀也不规则。同时,采用激光共聚焦显微镜也观察到CdMnTe富Te区存在无规律沉积的含有孔洞的不规则形状Te相。如果采用合适的生长工艺得到较为平直的生长界面,Te溶液垂直布里奇曼法可以有效减少CdMnTe晶体中的孪晶。