The decay kinetics of excitonic luminescence in AgCl crystals

The decay kinetics of the excitonic luminescence observed at 2.5 eV in AgCl after pulsed laser irradiation was measured in wide temperature (10-200 K), time (20 ns-10^-2 s) and luminescence intensity intervals. It is shown that, at low temperatures, the decay of luminescence is due to the static tunnelling recombination of unidentified shallow electron centres (with a wavefunction radius of about 30 AA) with immobile self-trapped holes. At temperatures above 80 K the relevant luminescence decay starts to differ from that at 10 K and does not obey the usual exponential or second-order kinetics; it was interpreted as diffusion-controlled annihilation within close (geminate) Frenkel pairs of radiation defects. These latter are assumed to be Ag ²⁺V_c^- and interstitial silver atoms Ag _i⁰, respectively. Silver atoms are characterized by the 0.15 eV activation energies of hops and a small wavefunction radius of about 1 AA. Thermal quenching of this luminescence is discussed; its activation energy (0.33 eV) corresponds to cation vacancy migration.