Crystal fields in (La1−xGdx)OCl:Eu3+ solid solutions

Abstract

The formation of cation solid solution in the (La1−xGdx)OCl:Eu3+ (0≤xGd≤1; ΔxGd=0.1) series was studied by photoluminescence spectroscopy. The luminescence from the 5D0–2 to the 7F0–4 levels of the Eu3+ ion in the (La1−xGdx)OCl series was recorded at 77 K by using argon ion laser excitation (457.9 nm). The interpretation of the spectra according to the C4v site symmetry of the Eu3+ ion in the tetragonal PbFCl-type structure yielded nearly complete sets (18 to 19 levels) for the 7F0–4 levels. Simulations of the Stark level schemes were carried out with the aid of a phenomenological c.f. theory utilizing the five non-zero c.f. Bqk parameters (B02, B04, B44, B06 and B46) allowed for the C4v site symmetry. By using the calculated c.f. parameter sets a quantitative measure was obtained to monitor the formation of cation solid solutions. The strength of the c.f. effect was estimated with the c.f. strength parameters S and Sk (k=2, 4 and 6). The c.f. parameter sets reproduced the experimental 7FJ (J=0–4) energy level schemes with the rms deviations between 4 and 11 cm−1. The individual parameters as well as the c.f. strength parameters were found to evolve in a smooth manner indicating complete solid solubility in the (La1−xGdx)OCl series. Some local distortions from the C4v symmetry — probably of long range—leading to the splitting of the 7F1 doubly degenerate E level were observed, however.