Nonlinear quenching of densely excited states in wide-gap solids

Dense interband electronic excitations on the order of 0.2 electron-hole pairs per nm${}^{3}$ are encountered in a number of circumstances of fundamental and practical significance. We report measurements of the kinetic order and rate constants of nonlinear quenching in pure and doped materials with band gaps in the range from 6 eV down to 1.4 eV. The principal method used can be described as interband $Z$-scan luminescence yield with subpicosecond pulse excitations. A clear delineation of second-order and third-order quenching kinetics is found between oxide and iodide insulating crystals. This delineation suggests that the hot-electron thermalization rate mediated by LO phonon frequencies governs whether free carriers can pair as excitons within the time period of nonlinear quenching.