Green luminescence and calculated optical properties of Cu ions in ZnO

TL;DR

This study uses ab initio calculations to analyze the optical properties of copper ions in ZnO, supporting Dingle's model that links green luminescence to a specific charge transition, and explains the absence of certain expected transitions.

Contribution

The paper provides the first ab initio analysis supporting Dingle's model for green luminescence in Cu-doped ZnO, clarifying the origin of specific optical transitions.

Findings

Supports Dingle's model for green luminescence

Achieves good agreement with experimental optical data

Explains the absence of a predicted radiative transition

Abstract

There are two characteristic optical transitions associated with Cu ions in ZnO, the 0.72 eV infrared and the 2.86 eV structured green luminescence (SGL). While the former is unambiguously related with the d(Cu2+) intra-shell transition, there is no generally accepted mechanism of the SGL. Besides the original model of Dingle [Phys. Rev. Lett. 23, 579 (1969)], two other mechanisms were recently proposed. We report an analysis of the optical properties of Cu in ZnO by ab initio calculations. The GGA+U approach is used, with the +U corrections applied to d(Zn), p(O) and d(Cu) orbitals. The results, compared with the available experimental data, support the Dingle's model, in which the SGL originates in the (Cu1+, hole) --> Cu2+ transition. A good agreement with experiment is obtained also for the internal transition at 0.72 eV. The absence of an expected radiative transition at about 2 eV is explained by its quasi-forbidden character.