Infrared Excitation of Visible Luminescence in Y 1 − x Er x F 3 via Resonant Energy Transfer
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The temperature and concentration dependences of the visible emission of ${\mathrm{Er}}^{3+}$ in Y${\mathrm{F}}_{3}$ under infrared excitation of the $^{4}I_{\frac{11}{2}}$ levels have been measured. The infrared radiation is absorbed by ions initially in the ground state and two excitations subsequently combine, yielding an ion in a higher-energy state. The temperature dependence of the $^{4}S_{\frac{3}{2}}\ensuremath{\rightarrow}^{4}I_{\frac{15}{2}}$ emission has a broad maximum at 90\ifmmode^\circ\else\textdegree\fi{}K. The reduction in the emission for $Tl90$\ifmmode^\circ\else\textdegree\fi{}K results from the depopulation of the higher-energy crystal-field-split levels of the $^{4}I_{\frac{11}{2}}$ manifold which have a resonant match with the $^{4}F_{\frac{7}{2}}$ levels. For $Tg90$\ifmmode^\circ\else\textdegree\fi{}K the emission is increasingly quenched by ion-pair relaxation from $^{4}S_{\frac{3}{2}}$ via $^{2}H_{\frac{11}{2}}$. For the concentration range $0.01lxl0.1$, the $^{4}S_{\frac{3}{2}}$ emission is proportional to ${x}^{2.9}$ at 77\ifmmode^\circ\else\textdegree\fi{}K and to ${x}^{1.3}$ at 295\ifmmode^\circ\else\textdegree\fi{}K.