Ultralong optical dephasing time in Eu(3+):Y(2)SiO(5).

We report what is to our knowledge the first measurement of linear and nonlinear spectroscopic properties for the (7)F(0)-(5)D(0) transition of Eu(3+):Y(2)SiO(5). Two clearly resolved lines at 579.879 and 580.049 nm, stemming from different sites, show dissimilar photoluminescence and hole spectra. In addition, these two sites have different inhomogeneous and homogeneous linewidths, which suggests that the local-field effect is smaller for one site. Specifically, the less affected site exhibits the longest dephasing time (822 micros) of any solid, which corresponds to a homogeneous linewidth of 387 Hz, and this linewidth is found to persist for hours without apparent spectral diffusion.