Zero-field splitting parameters and local structures for tetragonal Cr^(2+) centers in Cr^(2+)-doped ZnSe semiconductors

The inter-relation between zero-field splitting （ZFS） parameters and local lattice structures of the （CrSe4）6 clusters in ZnSe semiconductors has been established by using the complete diagonalization （of the energy matrix） method. On the basis of this, the local lattice distortions, the ZFS parameters D, a, F and the optical spectrum for Cr2＋ ions doped into ZnSe are theoretically investigated, and the contributions of the spin singlets have been taken into account. The calculated ZFS parameters are in good agreement with the experimental values. From our calculations, the tetragonal distortion parameters AR = 0.091A and Aθ = 4.28° of Cr2＋ in ZnSe are acquired, and the results suggest that there exists a tetragonal expansion distortion for the local lattice structure of （CrSe4）6- clusters in ZnSe crystals. The influence of the spin singlets on ZFS parameters is also discussed, indicating that the contributions to ZFS parameters a and F cannot be ignored.

高压下Cr2+:ZnSe的光学和力学性能

ZnSe是Ⅱ-Ⅵ族重要的半导体材料,在常温常压下是闪锌矿结构,在高压下会发生相变转变为岩盐矿结构。将过渡金属离子掺杂在ZnSe晶体中可以有效获得中红外区域的激光增益介质和光电材料。主要研究了高压对Cr^2+掺杂ZnSe半导体材料性质的影响。基于密度泛函理论的第一性原理,计算了掺杂剂(Cr^2+)的引入对ZnSe相变压强的影响,以及高压环境下ZnSe和Cr^2+:ZnSe晶体的电子结构、光学性能和力学性能的变化。Cr^2+掺杂降低了ZnSe从闪锌矿到岩盐矿结构的相变压强,并且掺杂浓度越高,相变压强越低。分析了ZnSe和Cr^2+:ZnSe的电子结构和光学性能,高压下晶体由半导体性质转变为金属性质。环境压力和高压下计算得到的弹性常数均满足稳定性条件,验证了晶体结构的机械稳定性。同时,高压下晶体较大的体积模量、剪切模量和杨氏模量说明岩盐矿结构具有更大的硬度和更高的稳定性。

高功率中红外激光器的进展

中红外激光器在光谱学、遥感、医疗、环保及军事等诸多领域都有重要的应用价值和发展前景,因此已成为各国研究的热门课题。首先介绍各类中红外光参量振荡器及其泵浦源的进展,而后介绍中红外单极型量子级联半导体激光器特点和进展。