Analysis of the 8S72 → 6PJ two-photon absorption transitions of Gd3+ in Cs2NaGdCl6

Abstract Measurements of the 8 S 7/2 → 6 P J , 6 I J two-photon transitions of Gd 3+ ions in the cubic elpasolite Cs 2 NaGdCl 6 are reported. The two-photon excitation spectra of the intense ultraviolet fluorescence exhibit two main features: (i) the predominance of the 8 S 7/2 → 6 P 7/2 lines, and (ii) the observation of the 6 P 3/2 and 6 I 7/2 states unobservable in one-photon absorption. Moreover, the two-photon transition intensities are well reproduced by extending the second order standard theory to include third order terms involving the spin-orbit interaction within the 4f 6 5d states. To this purpose we developed a crystal-field calculation that fit the experimental data quite well.