Selection rule violation, anisotropy, and anomalous intensity of two-photon absorption lines in Gd 3+:LaF 3

Abstract

Fluorescence detection following excitation with a pulsed dye laser is used to measure relative cross sections of 14 two-photon transitions within the 4f 7 configuration of the Gd 3+ ion in LaF 3. The transition intensities 8S 7 2 → 6I J , are anomalously large and strongly anisotropic and in three cases violate the selection rule ΔJ ⩽ 2. J-mixing of 4f 7 levels by the crystal field appears inadequate to explain this behavior, and an explanation employing crystal field mixing of levels of the 4f 6 5d configuration, which serve as intermediate states, is proposed.