High index of refraction via quantum interference in a three-level system of Er^3＋-doped yttrium aluminium garnet crystal

A simple three-level system is proposed to produce high index of refraction with zero absorption in an Er^3＋-doped yttrium aluminium garnet （YAG） crystal, which is achieved for a probe field between the excited state 4I13/2 and ground state 4I15/2 by adjusting a strong coherent driving field between the upper excited state 4I11/2 and 4I15/2. It is found that the changes of the frequency of the coherent driving field and the concentration of Er^3＋ ions in the YAG crystal can maximize the index of refraction accompanied by vanishing absorption. This result could be useful for the dispersion compensation in fibre communication, laser particle acceleration, high precision magnetometry and so on.

Crystallization and Luminescence Properties of Sm3＋-Doped SrO-Al2O3-SiO2 Glass-Ceramics

The Sm^（3＋）-doped SrO-Al2O3-SiO2（SAS） glass-ceramics with excellent luminescence properties were prepared by batch melting and heat treatment. The crystallization behavior and luminescent properties of the glass-ceramics were investigated by DTA, XRD, SEM and luminescence spectroscopy. The results indicate that the crystal phase precipitated in this system is monocelsian（SrAl2Si2O） and with the increase of nucleation/crystallization temperature, the crystallite increases from 66 % to 79 %. The Sm（3＋）-doped SAS glass-ceramics emit green, orange and red lights centered at 565, 605, 650 and 715 nm under the excitation of 475 nm blue light which can be assigned to the 4 G5/2→6 Hj/2（j=5, 7, 9, 11） transitions ofSm^（3＋）, respectively. Besides, by increasing the crystallization temperature or the concentration ofSm^（3＋）, the emission lights of the samples located at 565, 605 and 650 nm are intensified significantly. The present results demonstrate that theSm^（3＋）-doped SAS glassceramics are promising luminescence materials for white LED devices by fine controlling and combining of these three green, orange and red lights in appropriate proportion.

烧结时间对YBa_2Cu_3O_(7-δ)超导体的正交结构及正电子寿命参数的影响

报告了利用X射线衍射 (XRD)、扫描电镜 (SEM )和正电子湮没等实验对YBa2 Cu3 O7-δ(Y- 12 3)体系正交畸变度和正电子寿命谱随烧结时间变化的研究结果。发现在 95 0℃温度的烧结条件下 ,在 12— 72h这一相当宽的烧结时间范围内 ,正电子实验具有足够的稳定性和可靠性 ,实验表明足够的烧结时间在Y - 12 3多晶材料制备方面是必须的。

利用BaZrO_3涂层Al_2O_3坩锅生长YBa_2Cu_3O_(7-δ)单晶体

在常规 Al2 O3刚玉坩锅内表面制备 Ba Zr O3保护层的方法生长 YBa2 Cu3O7-δ高温超导单晶 .实验结果显示 ,在晶体生长过程中 ,这种 Ba Zr O3薄层确实可以有效地阻止坩锅材料中的 Al向 Y2 O3- Ba O- Cu O溶液的扩散 ,且生长出的 YBa2 Cu3O7-δ晶体中 ,在仪器精度范围内没有发现 Al杂质的存在 .刚刚生长没有进行氧退火处理样品具有四方对称性 ,晶格常数分别为 a=0 .385 86 nm,b=0 .385 83nm ,c=1.17931nm ,α=β=γ=90°.简单氧气氛下热处理后 ,超导转变温度由 45 K提高到 84K.

Optimum fluorescence emission around 1.8μm for LiYF_4 single crystals of various Tm^(3+)-doping concentrations

In this paper, optical spectra of LiYF4 single crystals doped with Tm3＋ ions of various concentrations are reported. The emission intensity at 1.8 ktm first increases with increasing Tm3＋ concentration, and reaches a maximum value when the concentration of Tm3＋ is about 1.28 mol%, then it decreases rapidly as the concentration of Tm3＋ further increases to 3.49 mol%. The emission lifetime at 1.8 p.m also shows a similar tendency to the emission intensity. The maximum lifetime of 1.8 μm is measured to be 17.68 ms for the sample doped with Tm3＋ of 1.28 mol%. The emission cross section of 3F4 level is calculated. The maximum reaches 3.76 × 10 -21 cm2 at 1909 nm. The cross relaxation （3H6, 3H4 →3 F4, 3F4） between Tm3＋ ions and the concentration quenching effect are mainly attributed to the change of emission with Tm3＋ concentration. The largest quantum efficiency between Tm3＋ ions is estimated to be ,-147% from the measured lifetime and calculated radiative lifetime. All the results suggest that the Tm3＋/LiYF4 single crystal may have potential applications in 2 μm mid-infrared lasers.

Ni doping effects in YBa_2Fe_3O_(8+w)

By doping Ni into YBa2Fe308＋w （YBFO） system, we obtained the phase YBa2Fe3-xNixO8＋w （YBFNO, x=0, 0.05, 0.10, 0.15, 0.30, 0.50, 1.00）. This paper discusses the changes in crystal structural, resistivity and magnetoresistivity （MR） of YBFO samples due to the incorporation of transition metal Ni. The results show that Ni substitution for partial Fe in YBFO does not substantially transform the structure of parent phase, but results in tiny changes in the lat- tice parameters. The YBFO crystal with Ni doped is semiconducting.

THE SUPERCONDUCTIVITY OF YBa_2Cu_3O_(7-δ) SYSTEM WITH TRANSITIONAL STRUCTURE FROM TETRAGONAL PHASE TO ORTHORHOMBIC PHASE

The intermediate YBa2Cu3O7-δ samples of single phase with transitional structure from tetragonal phase to orthorhombic phase are prepared by quenching at different temperatures and investigated systematically. From X-ray diffraction (XRD), R-T curve and ac susceptibility measurements, it can be concluded that the structure transits from tetragonal phase to orthorhombic phase as the quenching temperature decreases; the YBa2Cu2O7-δ samples with tetragonal phase are nonsuperconductive till 4.2K; the critical temperature depends on the degree of orthorhombic distortion in the intermediate samples; the possible existence of a structure phase transition near 100K for the non-superconductive tetragonal phase is discovered for the first time. The electrical conductance property at high temperature region (higher than 100K) for the samples quenched at higher temperature can be explained in terms of the affection of oxygen vacancies.

Yb^(3+):Gd_2SiO_5晶体的结构和光谱性能

采用提拉法成功生长尺寸为φ30 mm×75 mm的15at.%Yb^(3+):Gd_2SiO_5单晶,并用Reitveld全谱拟合方法确定了其晶格常数、原子坐标和温度因子等参数.用吸收光谱计算了Yb^(3+)离子~2F_(7/2)(?)~2F_(5/2)能级跃迁的振子强度、谱线强度、跃迁概率、能级寿命和积分发射截面等光谱参数,并根据激光性能评估得出结论:该晶体具有较大的阈值特性,有望采用大功率激光二极管泵浦实现可调谐或超快激光输出.

Yb···GdYCOB晶体涡旋激光器

采用光强分布为环形的半导体激光器端面抽运Yb…GdYCOB晶体,实现了激光谐振腔直接发射涡旋激光。通过测量输出激光光束的空间强度分布、光束品质因子、光束纯度以及光束的波前相位信息,证实激光器输出的光束为高纯度涡旋光束。当抽运功率为3.2W时,最大输出功率为281mW,光-光转换效率为8.7%,斜率效率为21.7%。