Anticorrelation between yields of recombination luminescence and recombination-induced defect formation in alkali-metal halides

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Abstract
Coupled rate equations are used to examine the premise that the anticorrelation of F-center formation yield and of self-trapped exciton luminescence in alkali-metal halide crystals is a consequence of thermally activated motion of a halogen interstitial atom (H center) relative to its complementary vacancy site (F center). In our treatment, the anticorrelation depends on relative rates of processes occurring on the lowest adiabatic potential surface connecting self-trapped excitons and F-H pairs, but is essentially independent of how that surface is populated from higher states. Thermally activated nonradiative decay to the electronic ground state must be disallowed if the anticorrelation is to hold. Conversely, a distinguishing feature of those alkali halides which do not exhibit the anticorrelation is the existence of a nonradiative channel for self-trapped exciton decay to the ground state. Since the present treatment was developed for conditions of thermal equilibrium, it cannot fully address the prompt (∼10 ps) formation of F centers at liquid-helium temperature or the ejection of energetic halogen atoms from the surface, as observed in some alkali halides of the latter group.