Spectroscopic properties of excited states of ions in glass measured using laser-induced fluorescence line narrowing

Laser-induced fluorescence-line-narrowing techniques are extended to measure site-to-site variations in the spectroscopic properties of excited states of optically active ions in glass. The crystalline Stark splitting associated with the initia excited state, rather than the terminal fluorescence state, is observed. The process is illustrated for ${\mathrm{Eu}}^{3+}$ in a lithium-borate glass by exciting the $^{5}D_{1}$ state and observing $^{5}D_{0}\ensuremath{\rightarrow}^{7}F_{J}$ fluorescence. The measured crystal-field splitting of $^{5}D_{1}$ is in good agreement with that predicted from the splitting of $^{7}F_{1}$. Conditions necessary for obtaining fluorescence line narrowing in excited states are discussed.