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Crystal Structure and Optical Properties of Defect-Chalcopyrite-Type MnGa2S4

The crystal structure of MnGa2S4 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 4T1(4G) to the ground state 6A1(6S) of the Mn2+ ion, because five photoluminescence excitation bands corresponding to five optical absorption bands are assigned to transitions from the ground state 6A1(6S) to the excited states 4T1(4G), 4T2(4G), 4E(4G)+4A1(4G), 4T2(4D) and 4E(4D). The role of the Mn2+ 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 Mn2+ ion is tetrahedrally coordinated by four S2- ions in both the defect-chalcopyrite-type MnGa2S4 and the zinc-blend-type Mn-doped ZnS.