改进BaF2闪烁体光输出特征研究

介绍旨在抑制BaF2闪烁体慢发光成分,拓展其应用领域的紫外滤光膜系设计和性能测量结果,研究表明,以Al2O3/MgF2/Al/MgF2为基本结构优化设计的紫外滤光膜系对来自BaF2闪烁体不同角度入射的快/慢成分光分别具有高透射和强截止特性.还提供了用纳秒级脉冲辐射源激发"BaF2+紫外滤光膜系+光电闪烁探测器"系统获得的BaF2闪烁体时间响应曲线,并对紫外滤光膜系中子辐照损伤特性进行了研究.     

闪烁晶体的发光研究进展

概述了近年来闪烁体发光研究的进展,主要介绍用于未来高能物理实验的新型闪烁体发光机理研究,选取我们在研BaF₂,BaF₂:RE,CeF₃以及PbWO₄中的一些新进展。重点谈及三点:(1)在BaF₂的“价带^→芯带”跃迁发光研究基础上进行稀土(Gd³⁺-Eu³⁺)掺杂时观察到的量子剪裁以及对多光子发光的新思考;(2)CeF₃晶体发光的级联能量传递中,Ce³⁺(290nm发射带)与缺陷发光中心(340nm发射带)间能量传递及其传递效率的温度依赖;(3)PbWO₄晶体的发光中心研究中,提出以“WO₄^-2+O_i”绿光中心替代“WO³+F”中心观点的依据。同时也简介了医用闪烁体的最新进展。     

助熔剂BaF2在制备BaSi2O5:Pb2+过程中的机理

采用高温固相合成法制备出BaSi₂O₅:Pb²⁺荧光体。考察了BaF₂的加入量对产物紫外发射强度的影响。用差示扫描量热分析,X射线衍射,光致发光光谱研究了掺入助熔剂BaF₂后BaSi₂O₅:Pb²⁺紫外发射强度显著增强的机理,并从热力学角度对实验结果作了分析。研究表明少量BaF₂的掺入加快了反应速度;降低了BaSi₂O₅:Pb²⁺形成温度,在高温下与SiO₂反应生成SiF₄气体,生成的SiF₄再与BaCO₃反应形成结晶良好的BaSi₂O₅:Pb²⁺荧光体。     

掺铋BaF2晶体的制备及其近红外发光研究

通过温度梯度法制备了Bi₂O₃:BaF₂以及BiF₃:BaF₂晶体.在Bi₂O₃:BaF₂晶体中观察到了发光峰位于961 nm,半高宽202 nm的超宽带红外发光.在BiF₃:BaF₂晶体中检测到Bi²⁺和Bi³⁺可见区的发光,但是没有观察到红外发光.通过γ射线辐照实现了BiF₃:BaF₂晶体的近红外发光, 发光峰位于1135 nm,半高宽192 nm.讨论了Bi₂O₃和BiF₃掺杂BaF₂晶体的红外发光的机理. 关键词： 近红外发光 铋 氟化钡晶体 γ辐照     

MgF2与Alq3(八羟基喹啉)反应的高分辨电子能量损失谱研究

介绍了用高分辨电子能量损失谱(HREELS)研究MgF₂与Alq₃(八羟基 喹啉)的反应.结果表明无论MgF₂蒸镀到Alq₃上或Alq₃蒸镀到MgF_{2上，MgF2与Alq3均发生了相同的反应.在反应中，对应于Alq3分子非平面苯环弯曲振动的能量损失峰位置发生了移 动.HREELS的研究结果表明从MgF2中的Mg与Alq3中的Al,O和N相互作用，Mg 的位置处于Alq3分子的平面外. 关键词： 2}')" href="#">MgF₂ 八羟基喹啉 高分辨电子能量损失谱     

MgF2:Mn2+光谱、超精细常数和局部结构的关联

基于电子顺磁共振(EPR)超精细常数A_s确定键长的新方法和半自洽场d轨道理论，对MgF₂:Mn²⁺光谱和EPR超精细常数作出了统一解释.得到室温下MgF₂:Mn²⁺晶体中杂质中心Mn—F的键长为0.2124±0.0010nm. 关键词： 晶体场 电子顺磁共振 光学和磁学性质     

YAG：Ce发光材料合成的助熔剂研究

采用高温固相法合成YAG:Ce荧光粉时,传统的以硼酸为助熔剂的产物硬度很大,处理过程中容易破坏晶体形貌,影响发光性能.采用氟化物助熔剂(MgF₂、CaF₂、SrF₂、BaF₂、AlF₃)及它们与H₃BO₃混合助熔剂来制备YAG:Ce,研究了助熔剂种类及其浓度对制得的粉体发光性能的影响,比较了它们的晶体形貌与物相组成.结果表明,采用不同助熔剂合成的YAG:Ce的激发光谱及发射光谱基本相同,而BaF₂、AlF₃、SrF₂及它们与H₃BO₃的混合助熔剂系列,可在一定程度上降低产品硬度、提高产品发光亮度;其中H₃BO₃~SrF₂系列、H₃BO₃~BaF₂系列的晶化程度与粒度分布均有改善;H₃BO₃~BaF₂系列的物相组成比较纯,除Y₃Al₅O₁₂主相外基本无杂相.     

高压下BaF2光学性质的模拟计算

探寻新的冲击窗口材料是高压科学领域中的一个重要课题.为此,在100 GPa范围内,通过第一性原理方法计算了BaF₂晶体的吸收谱以及在532 nm处的折射率.结果表明:1)压力和结构相变因素不会引起BaF₂晶体在可见光区域出现光吸收;氟和钡空位点缺陷的存在将使得BaF₂吸收谱的吸收边红移,但这些红移行为不会导致该材料在可见光区域内出现光吸收的现象,由此可以初步推测,BaF₂晶体有成为冲击窗口材料的可能. 2) BaF₂的折射率在其三个结构相区都随压力的增大而增大,并且BaF₂的高压相变也使得其折射率升高;钡空位点缺陷的存在将导致其折射率减小,而氟空位点缺陷却引起其折射率增加.     

BaF2-InF3系统中各个相的离子电导研究

在BaF₂-InF₃系统中存在一个萤石型固溶体Ba_1-xIn_xF_2+x(03(InF₆)₂和BaInF₅。测定了系统中各个相的电导率并和BaF₂-BiF₃系统进行比较。讨论了阳离子极化性和晶体共价性对电性能的影响。 关键词：     

Co2+离子在MgF2和ZnF2晶体中的各向异性g因子的理论研究

利用基于基团模型的3d⁷离子在斜方对称中的高阶微扰公式计算了MgF₂和ZnF₂晶体中Co²⁺杂质中心的各向异性g因子g_x，g_y和g_z. 在计算中，考虑了共价效应， 组态相互作用和斜方晶体场的贡献；而且与此相关的参量可由所研究的晶体的光谱和结构数据得到. 计算结果与实验符合较好.     

Charge states of the activator and size effects in BaF2: Eu nanophosphors

ABSTRACT

According to the spectra of stationary X-ray excited luminescence (XEL) of BaF₂: Eu nanophosphors at 80 and 294 K, it was revealed that the thermal annealing of fine-grained nanoparticles (d?=?35?nm) in the range of 400–1000°C, which is accompanied by an increase of their sizes in the range of 58–120?nm, does not result in effective changes of the charge state of Eu^{3 +} → Eu^{2 +} activator, in contrast to CaF₂: Eu nanoparticles. The maximum light output of X-ray excited luminescence of BaF₂: Eu nanophosphors in the 590?nm emission band of Eu³⁺ ion was observed at an annealing temperature of 600°C with the average size of nanoparticles 67?nm. The subsequent growth of annealing temperatures, especially in the range of 800–1000°C, causes decrease in the light output of X-ray excited luminescence due to the increase of defect concentration in the lattice as a result of sharp increase of nanoparticle sizes and their agglomeration. In BaF₂: Eu nanoparticles of 58?nm size, according to the thermostimulated luminescence (TSL) spectrum, transformation of Eu³⁺ → Eu²⁺ under the influence of long-time X-ray irradiation was revealed for the peak of 151?K. Thus, X-ray excited luminescence spectra of BaF₂: Eu nanophosphors are formed predominantly due to the emission of Eu³⁺ ions, while emission of Eu²⁺ ions is observed in the TSL spectra.     

A perturbed angular correlation spectrometer for material science studies

A four-detector perturbed angular correlation (PAC) spectrometer has been developed with ultra-fast BaF₂ detectors to acquire four coincidence spectra simultaneously, two at 180° and two at 90°. This spectrometer has double efficiency compared to that of a three-detector set-up. Higher efficiency is desirable for PAC studies in solid state physics where large number of coincidences are required to obtain the PAC spectra with good statistics and is particularly useful when the half-lives of the parent probe nuclei used for PAC measurements are ∼2–3 days or less as in ¹¹¹In (2.8 d), ⁹⁹Mo (2.7 d) and ¹⁴⁰La (1.7 d). The performance of the spectrometer has been tested for the HfO₂ monoclinic crystal in the temperature range from 77 to 873 K and for the HfF₄·3H₂O crystal at room temperature. The polycrystalline HfO₂ has been synthesized from Hf metal by heating in air. The hydrated hafnium fluoride has been crystallized by dissolving Hf metal in 40% HF and drying slowly at room temperature.      

10BaF2:NaF, Na3AlF6/TiO2 composite as a novel visible-light-driven photocatalyst based on upconversion emission

A rare-earth free upconversion luminescent material, 10BaF2：NaF, Na3AIF6, is synthesized by a hydrothermal method. The study of fluorescent spectrum indicates that it can convert visible light （550 nm-610 nm） into ultraviolet light （290 nm 350 nm）, and two emission peaks at 304 nm and 324 nm are observed under the excitation of 583 nm at room temperature. Subsequently, 10BaF2：NaF, Na3AIF6/TiO2 composite photocatalyst is prepared and its catalytic activity is evaluated by the photocatalytic reduction of CO2 under visible light irradiation （λ〉 515 nm）. The results show that 10BaF2：NaF, Na3AIF6/TiO2 is a more effective photocatalyst for CO2 reduction than pure TiO2, their corresponding methanol yields are 179 and 0 μmol/g-cat under the same conditions. Additionally, the mechanism of photocatalytic reduction of CO2 on 10BaF2：NaF, Na3AIF6/TiO2 is proposed.     

Thermoluminescence and opitical absorption of BaF2 crystals

Abstract

Nominally pure and Dy-doped BaF₂ crystals were investigated concerning their optical absorption (OA) and thermoluminescence (TL) properties. Peaks at 120—150 and 200°C were observed for a heating rate of 1.7°C/s. The TL response for γ-rays and the TL emission spectra were obtained for these peaks. Except for the purest crystal, all BaF₂ crystals produced OA bands before irradiation typical of Ce³⁺ ions. After irradiation, Dy doped crystals showed bands due to Dy²⁺ ions. A nominally pure sample gave bands related to Ce²⁺ ions and photochromic centers of Ce³⁺ ions. and photochromic centres of Ce³⁺ ions. The correlation between some OA bands and TL peaks is discussed.     

High energy implantation of buried insulating layers

Single crystals of CaF₂, SrF₂, and BaF₂ were irradiated at room temperature with alpha particles emitted from an effectively semi-infinite ²³⁸PuO₂ source to a cumulative dose of 3 × 10²⁰ alpha particles/m². Although no change in the lattice parameter of CaF₂ was observed, the crystals exhibited increasing coloration with dose. The lattice parameters of both SrF2 and BaF2 increased exponentially with dose, in agreement with a previously developed model, but the crystals developed no apparent coloration. Isochronal and isothermal-step annealing were used to study the recovery behavior of the lattice defects in both the SrF₂ and BaF₂ single crystals. A single recovery stage, tentatively associated with cation defects, was observed in each and the activation energy determined.     

强耦合磁失措自旋冰系统Dy2Ti2O7单晶生长和基本磁性质测量

利用红外光源浮区法生长出大尺寸、高质量的磁失措自旋冰化合物Dy₂Ti₂O₇单晶体.X射线衍射实验证实晶体具有面心立方结构，空间群为Fd3m，晶胞参数a＝1.0112(2) nm，［111］和［400］方向X射线衍射摇摆曲线半高宽分别仅为0.07°和0.05°.直流磁化率与温度关系测量给出晶体的Van Vleck顺磁因子为2.46×10^-5 m³/mol，有效磁矩μ_eff＝10.24(4)μ_B，Cure-Weiss温度Θ_CW＝1.1 K，揭示Dy₂Ti₂O₇具有弱的铁磁性.对磁性起源的综合分析表明，该自旋冰晶体磁性质主要来源于磁偶极相互作用，且相关最近邻长程偶极相互作用能量标度D_nn＝3.00 K. 关键词： 2Ti₂O₇')" href="#">Dy₂Ti₂O₇ 浮区法晶体生长 关联电子系统 自旋冰     

Spectral-kinetic characteristics of crystals and nanoceramics based on BaF<Subscript>2</Subscript> and BaF<Subscript>2</Subscript>: Ce

Optical characteristics of BaF₂ and BaF₂: Ce single crystals and nanoceramic materials prepared from these single crystals by uniaxial hot pressing have been studied. It has been shown that the introduction of Ce₃₊ ions into BaF₂ hardly affects the ultrafast (∼0.9 ns) luminescence component. The integrated luminescence intensity of the BaF₂: Ce nanoceramics is higher than that of the corresponding single crystal and considerably higher that the intensity of the undoped BaF₂ crystal. It has been demonstrated that the slow (several hundred nanoseconds) component of the luminescence decay of BaF₂: Ce is due to the energy transfer from excitons to Ce³⁺ ions.     

Phase relations for SrF2 TO 50 Kbars and 1900°C and its compression to 40Kbars at 25°C

The phase diagram of SrF₂ to 50 Kbars and 1900°C, obtained primarily by differential thermal analysis (d.t.a.), is presented. In analogy to the isostructural compound CaF₂, three solid phases, α, β, γ-SrF₂, as well as the liquid field, have been located. Thermochemical data (dT/dP, ΔV, ΔS) of the α-β and α-γ boundaries, and the melting curve are given. A tentative phase diagram for the isostructural compound BaF₂ is proposed. In addition, the first compression data for SrF₂ to 40 Kbars are reported. The bulk modulus, its pressure derivative, and the Grüneisen constant of SrF₂, CaF₂ and BaF₂ are compared.     

BH2和AlH2分子的结构及其解析势能函数

运用二次组态相关(QCISD)方法，分别选用6-311++G(3df,3pd)和D95(3df,3pd)基组，对BH₂和AlH₂分子的结构进行了优化计算，得到BH₂分子的稳态结构为C_2v构型，电子态为²A₁、平衡核间距R_BH=0.1187nm、键角∠HBH=128.791°、离解能D_e=3.65eV、基态振动频率ν₁(a₁)=1020.103cm^-1,ν₂(a₁)=2598.144cm^-1,ν₃(b₂)=2759.304cm^-1.AlH₂分子的稳态结构也为C_2v构型，电子态为²A₁、平衡核间距R_AlH=0.1592nm、键角∠HAlH=118.095°、离解能D_e=2.27eV、基态振动频率ν₁(a₁)=780.81cm^-1,ν₂(a₁)=1880.81cm^-1，ν₃(b₂)=1910.46cm^-1.采用多体项展式理论推导了基态BH₂和AlH₂分子的解析势能函数，其等值势能图准确再现了BH₂和AlH₂分子的结构特征及其势阱深度与位置.分析讨论势能面的静态特征时得到BH+H→BH₂反应中存在鞍点，活化能为150.204kJ/mol；AlH+H→AlH₂反应中也存在鞍点，活化能为54.8064kJ/mol. 关键词： 2')" href="#">BH₂ 2')" href="#">AlH₂ Murrell-Sorbie函数 多体项展式理论 解析势能函数     

氧氩比对SnO2/Ag/SnO2透明导电膜光电性能的影响

在室温及不同的氧氩比条件下,采用射频磁控溅射Ag层和直流磁控溅射SnO₂层,在载玻片衬底上制备出了SnO₂/Ag/SnO₂多层薄膜.用霍尔效应测试仪、四探针电阻测试仪和紫外-可见-近红外光谱仪等表征了薄膜的电学性质和光学性质.实验结果表明:当氧氩比为1:14时,所制得的薄膜的光电性质优良指数最大,为1.69×10^-2 Ω^-1;此时,薄膜的电阻率为9.8×10^-5 Ω·cm,方电阻为9.68 Ω/sq,在400~800 nm可见光区的平均光学透射率达85%;并且,在氧氩比为1:14时,利用射频磁控溅射Ag层和直流磁控溅射SnO₂层在PET柔性衬底上制备出了光电性质优良的柔性透明导电膜,其在可见光区的平均光学透过率达85%以上,电阻率为1.22×10^-4 Ωcm,方电阻为12.05 Ω/sq.