Luminescence and optically detected EPR of close F-center pairs in KCl

Abstract

By an appropriate optical treatment at room temperature the distance separating the members of F-center pairs can be decreased, giving rise to different optical and magnetic properties, revealed by the existence of a spin dependent nonradiative disexcitation mechanism. A model with an spin-spin exchange interaction is analyzed and compared with experiments at LHeT (variation of the luminescence with an applied magnetic field, optical detection of the EPR, and relaxation processes). The observed effects are related with population changes in the ground state caused by optical pumping and they are sensitive to the mixing of the states produced by the different interactions. The average exchange energy ranges between the hyperfine and the Zeeman energy depending on the state of aggregation. The EPR occurs in the ground state (g = 1.998, linewidth 52 (G) and the relaxation times range between 25 and 250 msec, depending on the optical pumping rate. The relation predicted by the model between the luminescence variation and the relaxation rate agrees with the experiments.