Homogeneous linewidth of the ⁵D₀-⁷F₀ transition of trivalent europium in a fluorophosphate glass

We measured the homogeneous linewidth of the ⁵D₀-⁷F₀ 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 Eu³⁺ in glass. The temperature dependence changes from T² at high temperatures to T^1.4 below 200 K. There are reports of linear variation of homogeneous widths with temperature for Eu³⁺ in glass, but all occur at much lower temperatures. The unusual behavior of Eu³⁺ in fluorophosphate glass may be related to the photoionization process used to produce Eu³⁺ from the Eu²⁺ ions found after melting glass with EuF₃.