Optical Properties of Er-Doped CuAlS 2

Photoluminescence (PL) spectra of Er-doped CuAlS2 single crystals grown by the chemical vapor transport technique were studied for the first time. Two kinds of crystals were prepared under different doping conditions, i.e., one was doped with Er alone (type I crystals) and the other were doped with Er and a very small amount of Fe (type II crystals). PL spectra of both type I and type II crystals showed three sharp emissions, at 2.34 eV (A-emission), 2.26 eV (B-emission) and 1.85 eV (C-emission), which were attributed to 2H11/2 →4I15/2, 4S3/2 →4I15/2 and 4F9/2 →4I15/2 f-f transitions of Er3+ ions, respectively. The intensity of f-f emisions in type II crystals was substantially larger than that in type I crystals. The emission peak at 2.34 eV (A-emission) has an excitation band at 3.24 eV, which is assigned to 4I15/2 →4G11/2 transitions of Er3+ ions on the Dieke diagram. In addition to the Er-related f-f emissions, a broad yellow-orange emission band was observed in both crystals at low temperatures. The yellow-orange emission dominated the room-temperature (RT) emission spectra of type I crystals, whereas the emission was almost quenched at RT in the case of type II crystals. The enhancement of Er-related emission and the quenching of the yellow-orange emission due to the presence of Fe impurity are discussed in terms of the site preference and the charge neutrality requirement.