Unified calculations of optical and EPR spectral data for two tetragonal Cu2+ centers in Cu2+-doped ZnO nanocrystals

•Optical and EPR data of two Cu2+ centers in ZnO nanocrystals are calculated.•Complete diagonlization method based on cluster approach is used in calculation.•Defect models of Cu2+ on the interstitial octahedral sites in ZnO are confirmed.•Defect structures of both Cu2+ centers are obtained.

Three optical band positions and four spin-Hamiltonian (or EPR) parameters (g factors g//, g⊥ and hyperfine structure constants A//, A⊥) of two tetragonal Cu2+ centers in Cu2+-doped ZnO nanocrystals synthesized at room temperature by mild and simple solution method are calculated from the complete diagonalization (or energy matrix) method based on the cluster approach (where the covalence effect due to the admixture between the orbitals of dn ion and ligands is considered). The calculations rest on the defect models suggested in the previous paper that both Cu2+ centers are Cu2+ on the interstitial octahedral sites in ZnO nanocrystals and the tetragonal elongations of octahedra are due to the static Jahn–Teller effect. The calculated results are in reasonable agreement with the experimental values. The defect models of both Cu2+ centers are therefore confirmed and their defect structures (i.e., the tetragonal elongations R//−R⊥) are acquired. The results are discussed.