Department of Physics, Shenzhen Institute of Research and Innovation, The University of Hong Kong, Pokfulam Road, Hong Kong, China.
Department of Applied Physics, Xi'an Jiaotong University, Xi'an 710049, China.
Sci Rep. 2017 Feb 2;7:41460. doi: 10.1038/srep41460.
The copper induced green luminescence (GL) with two sets of fine structures in ZnO crystal has been found for several decades (i.e., R. Dingle, Phys. Rev. Lett. 23, 579 (1969)), but the physical origin of the doublet still remains as an open question up to now. In this paper, we provide new insight into the mechanism of the structured GL band in terms of new experimental findings and theoretical calculations. It is found, for the first time, that the GL signal exhibits persistent afterglow for tens of minutes after the switch-off of below-band-gap excitation light but it cannot occur under above-band-gap excitation. Such a phosphorous property may be interpreted as de-trapping and feeding of electrons from a shallow trapping level via the conduction band to the Cu-related luminescence centers where the Cu ion is proposed to work as the final state of the GL emission. From first-principles calculation, such a Cu ion in wurtzite ZnO prefers a high spin 3d state with two non-degenerated half-filled orbitals due to the Jahn-Teller effect, probably leading to the double structures in photoluminescence spectrum. Therefore, this model gives a comprehensively new understanding on the mechanism of the structured GL band in ZnO.
几十年来，人们已经发现 ZnO 晶体中的铜诱导绿光（GL）具有两组精细结构（即 R. Dingle，Phys. Rev. Lett. 23, 579 (1969)），但双谱线的物理起源至今仍是一个悬而未决的问题。在本文中，我们根据新的实验发现和理论计算，对结构 GL 带的机制提供了新的见解。首次发现，在低于带隙激发光关闭后，GL 信号会持续数十分钟的余辉，但在高于带隙激发下不会发生。这种磷光特性可以解释为通过导带从浅陷阱能级中解陷并向与 Cu 相关的发光中心提供电子，Cu 离子被提议作为 GL 发射的最终态。基于第一性原理计算，由于 Jahn-Teller 效应，纤锌矿 ZnO 中的这种 Cu 离子优先具有高自旋 3d 态和两个非简并的半满轨道，这可能导致光致发光光谱中的双结构。因此，该模型对 ZnO 中结构 GL 带的机制提供了全面的新认识。
