Time-resolved photo-luminescence due to STE in TlBr doped with I− ions

Luminescence spectra have been measured in TlBr doped with iodine ions under pulsed-light excitation. Two broad emission bands were observed at 2.2 and 2.45 eV. The emission band at 2.2 eV decays non-exponentially below 20 K and was attributed to radiative annihilation of a localized exciton bound to an I− ion formed by tunneling a hole to an electron trapped at a distant lattice position. The emission band at 2.45 eV, which decayed with two time constants of 0.5 μs and less than 20 ns, was attributed to annihilation of a perturbed self-trapped exciton. The luminescence decay of the 2.45 eV band was analyzed by rate equations, assuming that the initial states of the emission were composed of doubly-degenerate singlet-triplet mixed states and a triplet state.