Interaction and energy transfer between divalent Sm ions andCN−molecular defects in KCl

Abstract

We studied the mutual interaction and electronic-vibrational energy transfer processes between divalent samarium ions and neighboring ${\mathrm{CN}}^{\ensuremath{-}}$ molecular impurities in KCl by the highly site-selective technique of combined excitation-emission spectroscopy as well as by vibrational ${\mathrm{CN}}^{\ensuremath{-}}$ luminescence (VL). We found for ${\mathrm{Sm}}^{2+}\ensuremath{-}{\mathrm{CN}}^{\ensuremath{-}}$ complexes involving just a single ${\mathrm{CN}}^{\ensuremath{-}}$ molecule that the spectral shifts of the intraconfigurational $(4f\ensuremath{\leftrightarrow}4f)$ transitions are very small, and are about 10 times bigger for the interconfigurational ${(4f}^{6}\ensuremath{\leftrightarrow}{4f}^{5}{5d}^{1})$ transitions. No measurable energy transfer from the electronic excitation into the vibrational ${\mathrm{CN}}^{\ensuremath{-}}$ stretch mode takes place for those centers, reflecting the weakly interacting character of the energetically lowest excited ${}^{5}{D}_{0}$ state which belongs to the $4f$-electronic configuration. However, for more complex centers which appear for higher ${\mathrm{CN}}^{\ensuremath{-}}$ concentrations and involve more than one ${\mathrm{CN}}^{\ensuremath{-}}$ molecule the more strongly coupled $5d$-type states are shifted to lower energy, even below the ${}^{5}{D}_{0}$ state. In this case $E\ensuremath{-}V$ energy transfer can be observed by the appearance of VL.