Magnetic field effect on the lifetime of the triplet state of theF2center in KCl and KBr

Measurements of the lifetime of the triplet state of the $F_2$ center in KCl and KBr in a magnetic field and at low temperatures are reported. The results can be quantitatively explained by a phenomenological theory assuming radiative decay; this theory needs only one adjustable parameter $n$ for each alkali halide studied. Polarization experiments on the phosphorescence of the defects confirm the value of this parameter deduced from the magnetic field experiments. Theoretical calculations of $n$ using the theory of Silsbee, Farge, and Ortega on radiative decay leads to good agreement with the experiments.