Studies on the defect structure for Cu2+ in CdSe nanocrystals

The defect structure for Cu²⁺ in CdSe nanocrystals is theoretically studied by analyzing the spin Hamiltonian parameters of this impurity center. This center is ascribed to Cu²⁺ occupying the octahedral interstitial site, rather than the tetrahedral substitutional Cd²⁺ site proposed by previous work. The Cu²⁺ center exhibits slight tetragonal elongation distortion (characterized by the elongation parameter ρ ≈ 0.03) due to the Jahn–Teller effect. The theoretical spin Hamiltonian parameters and optical transition show good agreement with the experimental data. The above unusual defect structure (occupation and symmetry) for Cu²⁺ in CdSe nanocrystals is discussed, as compared with the conventional trigonally distorted tetrahedral Cu²⁺ centers in bulk II–VI semiconductors.