${\mathrm{Pb}}^{2+}$→${\mathrm{Mn}}^{2+}$ nonradiative energy transfer in KBr

The analysis of optical emission and excitation spectra of KBr single crystals doubly doped with ${\mathrm{Pb}}^{2+}$ and ${\mathrm{Mn}}^{2+}$ ions has been accomplished for different sample conditions. The results show that highly efficient nonradiative energy transfer occurs from ${\mathrm{Pb}}^{2+}$ to ${\mathrm{Mn}}^{2+}$ ions which then decay by giving orange-red (640 nm) emission. A comparison of excitation spectra for manganese emission of as-grown and annealed samples shows that ${\mathrm{Mn}}^{2+}$ excitation is associated with the aggregated phase of ${\mathrm{Pb}}^{2+}$ ions. The 640-nm emission has been explained on the basis of a model which proposes trapping of ${\mathrm{Mn}}^{2+}$ ions in the Suzuki phase of ${\mathrm{Pb}}^{2+}$ dipoles. The electron-paramagnetic-resonance results also support this model. The results for annealed and subsequently aged samples are further in conformity with the model. Finally, the observed 520-nm emission band in as-grown samples has been attributed to a Suzuki-type aggregated phase of ${\mathrm{Mn}}^{2+}$ ions.