Sensitized Luminescence of Pure and Doped NaNO2 Single Crystals. III. Excitation Spectroscopy and Time-Resolved Trap Fluorescence

Energy transfer processes in the first excited state of NaNO2 single crystals doped with KNO2 are studied using fluorescence exciation spectroscopy and time resolved spectroscopy of the trap fluorescence. In the latter case either pulse excitation of the host excitons or selective resonant pulse excitation of trap states is used. Three pairs of trap states, each of which consists of a shallow trap (trap depth less than 100cm^-1) and a deep trap (trap depth in the order of 1000cm^-1), are identified. At low temperatures energy transfer from the shallow to the deep trap is effective only within the pair. At higher temperatures the shallow trap can also transfer the excitation energy to the host exciton band. The temperature dependence of these processes is discussed on the basis of the generalized master equation.