Temperature Dependence of the Lifetimes of the 1Σu+ State of STE in KI, NaCl, KBr and RbBr Crystals

The decay time ( τ σ d ) of the σ emission intensity has been observed in temperature range of 5 K ∼200 K by using a pulsed electron beam in picosecond range. τ σ d in KI, NaCl, KBr and RbBr are 1.9 ns (7.4 K), 3.0 ns (∼5 K after Blair et al. ), 3.7 ns (5.7 K) and 4.0 ns (5.6 K), respectively, and start to decrease to 100 ps or less above nearly 70 K, 40 K, 30 K and 20 K depending on the crystal. The activation energy for such thermal quenching of τ σ d are 46.2 meV, 32.0 meV, 22.1 meV and 14.7 meV. The capture process of the conduction electron by the self-trapped hole and the non-radiative decay of the self-trapped exciton are discussed.