Theory of Self-Trapped Exciton Luminescence in Halide Crystals

Abstract

A detailed phenomenological theory of the triplet luminescence from self-trapped excitons in halide crystals is developed. Energy levels and wave functions are obtained by constructing and diagonalizing a Hamiltonian matrix. Coupled rate equations for the decay of the three lowest triplet levels are solved for the general case in which the levels are not in thermal equilibrium, and circular polarizations, light intensities, and excited-state lifetimes are obtained as functions of temperature, magnetic field, and crystal orientation. KI and CsI excitons are used as detailed examples; the latter is of particular interest because it appears to exhibit a level crossing at ∼45 kG. The theory is also appropriate to other systems, including the excited $M$ center and the relaxed excited ${\mathrm{Tl}}^{+}$ ion in alkali halides.