High resolution spectroscopy of the 7F0↔5D0 transition in Eu3+:KYF4

In this paper we report the inhomogeneous and homogeneous linewidths of the 7F0↔5D0 optical transition for a number of sites in Eu3+:KYF4. The high frequency resolution obtained in our measurements enabled a sixth europium site to be identified, which was previously unresolved. In addition, preliminary hole burning measurements allow a partial characterization of the 153Eu isotope hyperfine spin states for two sites and an approximation of the ground-state spin-level lifetime. We also discuss the temperature dependence of the homogeneous linewidth, which was measured by a two-pulse photon echo study. This study is the first photon echo measurement reported for Eu3+ ions in fluoride crystals. The results demonstrate that the low temperature homogeneous broadening is not limited by magnetic contributions but rather by dynamic disorder modes. These measurements also reveal electron-phonon interactions that are significantly different to oxide crystals.