Investigation and simulation of the structural and electronic properties of LiF:Mg,LiF:Cu,LiF:P nano-layer dosimeters

In this study, electronic structure of lithium fluoride thin films in pure state and doped with magnesium (Mg), copper (Cu) and phosphorus (P) impurities was studied using WIEN2K Code. The structural and electronic properties of two LiF thin films with 1.61 and 4.05?nm thicknesses were studied and compared. Results show that the distance of atoms in the surface and central layers of pure LiF are 1.975 and 2.03?nm, respectively. Electronic density of the valence band around the surface atoms is greater than that around middle atoms of the supercell. The band gap of bulk LiF is 9?eV. But, in the case of thin films, it is reduced to 2?eV. Electronic and hole-traps were not observed in composition of LiF thin films doped with Mg and P with 1.61 and 4.05?nm thickness and in fact, metallic properties were observed. When Cu atoms were doped in composition of an LiF thin film, the thin film was converted to semiconductor.     

Thermoluminescence glow-curve characteristics of LiF phosphors at high doses of gamma radiation

High doses of ionising radiation are becoming increasingly common for radiation-processing applications of various medical, agricultural and polymer products using gamma and electron beams. The objective of this work was to study thermoluminescence (TL) glow-curve characteristics of commonly used commercial LiF TL phosphors at high doses of radiation with a view to use them in dosimetry of radiation-processing applications. The TL properties of TLD 100 and 700 phosphors, procured from the Thermo-Scientific (previously Harshaw) company, have been studied in the dose range of 1–60 kGy. The shift in glow peaks was observed in this dose range. Integral TL responses of TLD 100 and TLD 700 were found to decrease as a linear function of dose in the range of 5–50 kGy. The paper describes initial results related to the glow-curve characteristics of these phosphors.     

微量Mg/F表面梯度渗透改善高电压LiCoO2界面脆弱

采用高温固相法在1 050 ℃下烧结，制备了LiCoO₂低浓度梯度改性样品，分别为LiF掺杂包覆(LCOLF、LCO@LF)和MgF₂掺杂包覆(LCOMF、LCO@MF)。通过光电子能谱、透射电子显微镜和电化学技术等表征方法，对比分析材料形貌及电化学性能。结果表明，体相掺杂复合电极中，LCOLF热重测试显示出最优热稳定性，LCOMF晶体中(003)和(104)晶面间距收缩；45 ℃下 1C 倍率循环 70圈后，LCOLF 和 LCOMF 比容量分别为 141.45和 166.98 mAh·g^-1，循环性能优于 LiCoO₂。表面包覆复合电极中，LCO@LF和 LCO@MF晶粒表面光洁且晶格氧键价都向更高结合能方向增强；LCO@MF构建了坚实且紧密的包覆层，循环70圈后，放电比容量和容量保持率分别为 183 mAh·g^-1和 91.26%(LCO@LF分别为 154.38 mAh·g^-1和 77.54%)，循环性能显著优于体相掺杂。     

冲击压缩下单晶LiF高压声速及卸载路径研究

 采用二级轻气炮加载手段，在5~79.1 GPa冲击压力范围内，利用加窗VISAR技术对氟化锂（LiF）单晶样品进行了研究，得到了不同冲击压力下的纵波声速、体积声速以及卸载路径。实验结果显示：单晶LiF沿冲击绝热线的Lagrange纵波声速随粒子速度呈线性变化；在5~79.1 GPa冲击压力下，单晶LiF并未发生熔化及其它相变；卸载路径及速度剖面弹塑性明显。     

Kinetic simulation of charge transfer following 5.08 eV (F band) optical excitation of irradiated LiF:Mg,Ti (TLD-100): Participation of holes released via V3-VK transformation

Kinetic simulations of charge transfer in the framework of the conduction band/valence band model are described which investigate the effect of 5.08 eV photon bleaching on the optical absorption spectrum of irradiated LiF:Mg,Ti (TLD-100). The decrease in intensity of the 3.8 eV and 4.3 eV bands, newly discovered sub-entities of the 4.0 eV composite band, is interpreted as arising from the participation of holes released by capture of electrons at V₃ two-hole-centers. The simulations also require highly efficient electron transfer from the excited state of the F center to the V₃ center which is necessary to guarantee an adequate supply of released holes following the V₃-V_k transformation.     

强冲击压缩下LiF,Al2O3和LiTaO3 单晶的透光性

在二级轻气炮上,用高速电子相机扫描照相技术和改进的Mallory实验装置,对z切LiF,Al2O3(蓝宝石)和LiTaO3单晶材料的冲击透光性进行了对比测量,并用黑密度计提取出动态图像定量化的光强对比度变化曲线.结果表明,LiF单晶在102GPa压强下能够保持长时间的初始透光性不变,与公认的LiF具有优良的高压下透明性的认识一致.LiTaO3单晶在实验压力(139GPa)下变成基本不透明.而Al2O3单晶在131GPa冲击压力下则表现为透明性逐渐下降直至完全不透明.     

Application of two kinetic methods to evaluate the trap energy of lithium fluoride + sodium fluoride thermoluminescent phosphor

A mixture of equal quantities of powdered LiF and NaF was doped with 0.2% each of Ti, Mg and Mn and heated to obtain a LiF+NaF phosphor. After grinding and sieving, the thermoluminescent phosphor was used to obtain the thermoluminescence characteristics such as the glow curve; the dose-response curve, sensitivity, reproducibility and linearity were all established. The main goal was to introduce two new methods for the calculation of trap energy: the single-peak-differential and single-peak-integration methods, both modifications of the basic method of Randall-Wilkins. The plots used to calculate the trap energy were In[(d/dT)1/(1-)]vs. 1/T and ln[ln(1-)/(T _o-T)]vs. 1/T, respectively. These linear plots with slopes of (E/k) gave trap energies ofE=0.547 eV andE=0.551 eV, respectively.     

AlO_x/LiF composite protection layer for Cr-doped(Bi,Sb)_2Te_3 quantum anomalous Hall films

We have realized robust quantum anomalous Hall samples by protecting Cr-doped(Bi,Sb)_2Te_3 topological insulator films with a combination of LiF and A1O_x capping layers.The AlO_x/LiF composite capping layer well keeps the quantum anomalous Hall states of Cr-doped(Bi,Sb)_2Te_3 films and effectively prevent them from degradation induced by ambient conditions.The progress is a key step towards the realization of the quantum phenomena in heterostructures and devices based on quantum anomalous Hall system.     

Growth and characterization of LiF single crystal fibers

Single crystal LiF fibers have been grown by the micro‐pulling‐down (µ‐PD) technique. The fibers are 0.6 mm in diameter and 100 mm in length and of good optical quality. We describe the experimental apparatus for growth and analyze the sample structure and its spectroscopic characteristics. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Li1+δNi1-xCoxO2-yFy的合成与电化学性能研究

采用固相反应法在空气气氛下合成了同时掺杂Co阳离子和F阴离子的镍系正极材料Li_1+δNi_1-xCo_xO_2-yF_y(0≤δ≤0.2, 0≤x≤0.5, 0≤y≤0.1),考察了不同来源的镍源为原料对目标材料性能的影响,并采用XRD, SEM, TEM, BET,激光粒度分布,电化学性能测试等手段对该材料进行了表征.结果表明,在正极材料LiNiO₂中同时掺杂Co阳离子和F阴离子后合成的Li_1+δNi_1-xCo_xO_2-yF_y镍系正极材料具有完整的层状结构、均一的表面形貌、较好的粒径分布和良好的电化学性能.在20～25℃,充放电电流为0.15～0.25 mA,截止电压为4.25～2.70 V,充放电速率为0.2～0.5 C,电流密度为0.2～0.5 mA/cm²条件下,LiNi_0.8Co_0.2O_1.95F_0.05的首次充放电容量分别达到165.70 mAh/g和146.10 mAh/g,而且循环稳定性能良好,在恒流充放电循环50次后,其可逆放电容量大于140 mAh/g.这主要归因于具有较高电负性的F阴离子的掺入改善了正极材料的结够稳定性和Co与F离子的协同作用.该正极材料初步显示了实际应用的可能性.