Optical transitions of ${\mathrm{Er}}^{3+}$ ions in RbMg${\mathrm{F}}_3$ and RbMg${\mathrm{F}}_3$: Mn

Optical absorption, emission, and excitation spectra, as well as lifetime values, are presented for ${\mathrm{Er}}^{3+}$ ions in RbMg${\mathrm{F}}_3$. Previous workers have demonstrated that ${\mathrm{Er}}^{3+}$ ions can reside in a number of different site symmetries in crystalline hosts such as Ca${\mathrm{F}}_2$ and Cd${\mathrm{F}}_2$. The numerous sites in this type lattice are most likely due to compensating fluorine interstitials which are necessarily present for charge compensation. In a unit cell of RbMg${\mathrm{F}}_3$ there are two nonequivalent ${\mathrm{Mg}}^{2+}$ sites with $C_{3v}$ symmetry. Evidence is presented in this paper that ${\mathrm{Er}}^{3+}$ ions in RbMg${\mathrm{F}}_3$ substitute for ${\mathrm{Mg}}^{2+}$ ions in both types of sites. The charge compensation is not local, which leaves the symmetry of the ${\mathrm{Er}}^{3+}$ sites unchanged. Absorption data for ${\mathrm{Er}}^{3+}$-ion transitions in both sites are shown. Emission from ${\mathrm{Er}}^{3+}$ ions is observed from one type of site in RbMg${\mathrm{F}}_3$ and from both types of sites in RbMg${\mathrm{F}}_3$: Mn. Lifetime values for the ${}_{}{}^4{}_{}{}^{}S_{\frac{3}{2}}^{}{}_{}{}^{}$ and ${}_{}{}^4{}_{}{}^{}F_{\frac{9}{2}}^{}{}_{}{}^{}$ transitions are shorter than those normally measured in fluoride host lattices, and the emissions are quenched above 200 K. Energy migration among ${\mathrm{Er}}^{3+}$ ions and subsequent energy transfer to ${\mathrm{Mn}}^{2+}$-ion impurities are responsible for the steady-state and transient-emission behavior.