Cr3+ in diffusion doped Cr2+:ZnS

Characteristic absorption bands of Cr3+ peaked at 425 nm and 600 nm were observed in high optical quality Cr2+:ZnS prepared by the diffusion method, which were attributed to the Cr3+ ion in an interstitial octahedral coordination site. The corresponding transition scheme was analyzed based on the ligand field theory. Further research indicated a positive correlation between Cr3+ concentration and Cr doping level as well as oxygen partial pressure. DFT calculations of formation energies for different defect combinations confirm the spontaneous emergence tendency of Cr3+ during diffusion process with a preference for interstitial, S2−-octahedrally coordinated site. At the same time the presence of O2− at an interstitial site could further lower the system energy as well as providing charge compensation, thus increasing the Cr3+ concentration.