Title: First-principles study of the electrical and optical properties of Cr2+ doped ZnSe
Speaker: Zhang Yuqin
Time: 21st December 2018,11:00 am
Location: 816 Conference Room, Communication building
The first-principles calculations can be used to predict experimental results, and also to help interpret experimental observations, is a powerful tool for predicting new materials and their properties. In our work, first-principles calculations of the electronic structure and optical properties of Cr2+: ZnSe were performed. For Cr2+ doped ZnSe bulk crystal, the Cr2+ concentration and uniformity on the influence of their properties was studied. The results show that the absorption peak intensity and peak width decrease with diminishing Cr2+ concentration and a red-shift is observed in the absorption spectra. Cr2+ unhomogeneity makes the crystal changes from isotropic to anisotropic. The mechanism of the absorption and photoluminescence processes in Cr2+ doped ZnSe was then analyzed. When Zn is replaced by Cr atom, impurity bands are created in the bandgap and additional absorption peak appears in infrared region. These isolated impurity bands are mainly made up of Cr(d) orbitals, which are split into e and t2 groups because of the potential of the crystal field. The additional absorption and luminescence appears in infrared region are assigned as the transitions between e and t2 of Cr2+ ions in ZnSe. For Cr2+ doped ZnSe nanocrystalline, the morphology and size of particles on the influence of their performance was further researched. It shows that with the decreasing of the particle size, the bandgap of the ZnSe is increasing, which can be explained by the quantum size effect. Quite unexpectedly, the calculated results showed that the energy level splitting of the Cr(d) orbitals is decreasing when the size of particles reduced.
Key words: Cr2+ doped ZnSe, laser gain media, first-principles, electrical and optical properties