Visible anti-Stokes emission of Gd3+ in Cs2NaGdCl6 crystal

Visible emission, assigned to the transitions between the upper excited levels of Gd3+ in the Cs2NaGdCl6 crystal upon excimer laser excitation, was observed. The emitting level is covered by the intense 4f65d bands. The observed anti-Stokes transitions result from a two-photon absorption, the nature of which is discussed. Two mechanisms may have contributed to the observed visible signal: excited state absorption and two-photon absorption where the intermediate state belongs to the 4f7 configuration.