Excited-state absorption by Eu2+ in KBr, KCl, and NaCl

Excited-state-absorption (ESA) measurement have been made on alkali halide crystals doped with Eu2+, including both as-received and thermally quenched samples. No ESA has been detected in the visible spectral region, but strong excited-state absorption occurs in the near ultraviolet. This is in qualitative agreement with the published excited-state ionization model of ESA in CaF2:Eu2+. However, the observed ESA onset energies in alkali halides are significantly lower than predicted by that model, and are more nearly consistent with a charge-transfer transition. The ESA spectra show little evidence of ground-state depletion, and together with data on the fluence dependence of fluorescence and laser transmission, this suggests that the quantum efficiency of Eu2+ in these hosts is rather low.