The decay kinetics of excitonic luminescence in AgCl crystals

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Abstract
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 Ag2+Vc- and interstitial silver atoms Agi0, 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.

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