Radiationless processes in KCl:Eu²⁺(time-resolved and photoacoustic spectroscopy)

Several zero-phonon lines are observed in the fluorescence spectrum at low temperatures and annealing experiments show that these are associated with aggregation of Eu 2+ -K + vacancy pairs. Time-resolved spectroscopy measurements show that energy transfer takes place from ions in non-aggregated sites to those in aggregated centres. The time dependence is consistent with resonant electric dipole-dipole interaction with no back-transfer taking place. The vibronic sideband of the major zero-phonon line is analysed with a computer iteration process to determine one-phonon and multiphonon contributions. The thermal dependence of the width and position of the major zero-phonon line is shown to be consistent with strong coupling to only the low-frequency phonon modes. Non-radiative decay processes at room temperature are characterised by comparing fluorescence excitation and photoacoustic spectra.