Detailed site-selective spectroscopy has been performed as a function of temperature on the 7 F 0 ↔ 5 D 0 transition of Eu 3ϩ :Y 2 SiO 5 for Eu 3ϩ concentrations of 0.02%, 0.1%, 0.5%, and 1%. Time-domain optical dephasing, spectral hole lifetimes, anisotropic absorption coefficients, inhomogeneous linewidths, and fluorescence lifetimes for Eu 3ϩ ions at both crystallographic sites were measured. The temperature dependence of the optical dephasing, transition energy, and linewidth of the 7 F 0 → 5 D 0 absorption was measured and interpreted in terms of Raman scattering of phonons. Photon echo measurements of optical dephasing gave T 2 values as long as 2.6 ms, approaching the limit set by the fluorescence decay time. Spectral hole lifetimes were measured for temperatures from 2 K to 18 K, with observed lifetimes varying from 1 s at 18 K to an estimated value of greater than 20 days at 2 K. Anisotropic absorption coefficients were measured, and an increase in Eu 3ϩ concentration from 0.02% to 7% produced an increase in the inhomogeneous linewidth ⌫ inh from 0.5 GHz to ϳ150 GHz, indicating that Eu 3ϩ doping induces significant strain in the crystal. New determinations of many energy levels of 7 F J multiplets have been made for Jϭ0 to 6.

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