Homogeneous linewidth of theD05−F07transition of trivalent europium in a fluorophosphate glass

We measured the homogeneous linewidth of the ${}_{}{}^5{}_{}{}^{}D_0^{}{}_{}{}^{}-{}_{}{}^7{}_{}{}^{}F_0^{}{}_{}{}^{}$ transition of trivalent europium in a fluorophosphate glass using resonant fluorescence line narrowing between 20 and 295 K. The linewidth at 295 K is a factor of 10 smaller than typical for ${\mathrm{Eu}}^{3+}$ in glass. The temperature dependence changes from $T^2$ at high temperatures to $T^{1.4}$ below 200 K. There are reports of linear variation of homogeneous widths with temperature for ${\mathrm{Eu}}^{3+}$ in glass, but all occur at much lower temperatures. The unusual behavior of ${\mathrm{Eu}}^{3+}$ in fluorophosphate glass may be related to the photoionization process used to produce ${\mathrm{Eu}}^{3+}$ from the ${\mathrm{Eu}}^{2+}$ ions found after melting glass with Eu${\mathrm{F}}_3$.