Energy-transfer mechanisms in the KCl:Eu2+,Mn2+system

Energy-transfer mechanisms have been examined in the KCl:${\mathrm{Eu}}^{2+}$,${\mathrm{Mn}}^{2+}$ system at low Eu- and Mn-ion concentrations. The Eu ions represent the donor system, the Mn ions the acceptor one. No transfer evidence has been found in quenched samples; by annealing the samples at temperatures higher than 200 °C, the typical ${\mathrm{Mn}}^{2+}$ emission is observed after excitation in the ${\mathrm{Eu}}^{2+}$ absorption band. The energy-transfer mechanisms have been examined along the aggregation process induced by annealing the KCl:${\mathrm{Eu}}^{2+}$,${\mathrm{Mn}}^{2+}$ samples at 225 °C for very long times: three different types of behavior have been evidenced. In the early annealing stages a single pair donor-acceptor transfer mechanism is observed, while at longer annealing times an energy diffusion in the donor system, followed by a phonon-assisted transfer, takes place. Finally, at very long annealing times the energy diffusion process is followed by a resonant transfer mechanism.