Frequency Upconversion in YF3: Yb3+,Tm3+

Abstract

The stepwise conversion of infrared ($\approx 0.97\mu$) radiation to near infrared (0.81 μ) and visible (0.475 μ) light in Y${\mathrm{F}}_3$ sensitized with ${\mathrm{Yb}}^{3+}$ and activated with ${\mathrm{Tm}}^{3+}$ has been studied in detail. The lifetimes and fluorescence intensities of the important manifolds ($\mathrm{Yb}{}_{}{}^2{}_{}{}^{}F_{\frac{5}{2}}^{}{}_{}{}^{}$, $\mathrm{Tm}{}_{}{}^3{}_{}{}^{}H_4^{}{}_{}{}^{}$, $\mathrm{Tm}{}_{}{}^3{}_{}{}^{}F_4^{}{}_{}{}^{}$, and $\mathrm{Tm}{}_{}{}^1{}_{}{}^{}G_4^{}{}_{}{}^{}$), as well as the Yb-to-Tm transfer probability coefficients for the three steps of the process, have been measured as functions of concentration. A saturation effect previously observed in the Tm emission versus infrared excitation intensity has been shown to result from the rate of depopulation of $\mathrm{Tm}{}_{}{}^3{}_{}{}^{}H_4^{}{}_{}{}^{}$ by the second Yb-to-Tm transfer exceeding the $\mathrm{Tm}{}_{}{}^3{}_{}{}^{}H_4^{}{}_{}{}^{}$ decay rate. This was used to determine the second transfer probability coefficient. The first transfer probability coefficient was found to be 1.2×${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^3$ ${\sec }^{-1\mathrm{}}$ independent of Tm concentration and for Yb concentration of the order of 10 at.% and greater. The second transfer probability coefficient was found to be approximately ${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^3$ ${\sec }^{-1\mathrm{}}$ for Yb concentrations of 25 at.% and greater. The third transfer probability coefficient was found to be 2.7×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^3$ ${\sec }^{-1\mathrm{}}$. The dependence on Yb concentration of the relative efficiency of conversion to 0.475-μ light agrees well with the values calculated from a rate-equation model using the measured lifetimes and transfer probability coefficients.