We have investigated the temperature dependence of temporal behaviors of the A X and A T luminescence bands in NH 4 Cl:Tl + single crystals under an ArF excimer laser excitation. The time-resolved A X luminescence spectra reveal the existence of two luminescence bands which are attributed to the radiative transitions from the relaxed 3 T 1u and 3 A 1u states, respectively. The slow decay of the luminescence due to the transition from the 3 A 1u state in the A X band becomes fast with increasing temperature from 16 K to 27 K. Then, the A T band exhibits a temporal rise reflecting the non-radiative transition from the A X to A T minima on the adiabatic potential energy surface for the 3 A 1u state. The temperature dependence of the slow decay time of the A X band is analyzed by using the WKB method considering the non-radiative transitions from vibrational energy levels in the adiabatic potential well. As a results, the temperature dependence can be fitted by taking the TA phonon energy of the NH 4 Cl bulk crystal as the separation energy between the vibrational energy levels.