Abstract
)This paper reports the observation of time-resolved luminescence from a self-trapped exciton (STE) localized at tetrahedral (WO4) 2− complex anion in PbWO4. The results clearly reveal that the STE luminescence is composed of three emission bands peaking at 407, 425, and 450 nm. Such a composite nature is explained well by assuming that the lowest triplet states of the STE split into three sublevels owing to the symmetry lowering from Td to C3v due to the Jahn-Teller effect. This assumption is in accordance with the theoretical prediction of Bacci et al. The decay curve of each component and its temperature dependence are investigated in the range of 77 to 300 K. These results are discussed on the basis of an adiabatic potential energy diagram of the triplet STE state. Time-resolved luminescence spectra are also measured for Mo-doped PbWO4 crystals. From a comparison with the spectra of undoped PbWO4 crystals, the Mo-related luminescence is clearly separated from the intrinsic luminescence due to STEs.
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