Crystal Structure and Optical Properties of Defect-Chalcopyrite-Type MnGa_2S_4

摘要

The crystal structure of MnGa_2S_4 grown by the iodine transport method was refined by Rietveld analysis of its powder X-ray diffraction data, and it was confirmed to be the defect chalcopyrite structure. No emissions can be observed near the absorption edge region, but a red broad emission band having an asymmetric spectral shape with a low-energy tail is observed in the deep region at room temperature. The red broad emission band is considered to be due to the transition from the lowest excited state ~4T_1(~4G) to the ground state ~6A_1(~6S) of the Mn~(2+) ion, because five photoluminescence excitation bands corresponding to five optical absorption bands are assigned to transitions from the ground state ~6A_1(~6S) to the excited stales ~4T_1(~4G), ~4T_2(~4G), ~4E(~4G)+~4A_1(~4G), ~4T_2(~4D) and ~4E(~4D). The role of the Mn~(2+) ion with respect to the luminescence property of the defect-chalcopyrite-type MnGa2S4 is similar to its role with respect to the luminescence property of zinc-blend-type Mn-doped ZnS. This is reasonable because the Mn~(2+) ion is tetrahedrally coordinated by four S~(2-) ions in both the defect-chalcopyrite-type MnGa_2S_4 and the zinc-blend-type Mn-doped ZnS.