Spectroscopic characteristics of langasite (La3Ga5SiO14) and langatate (La3Ga5.5Ta0.5O14) crystals doped with Eu3+

The spectroscopic properties of two partially disordered crystals langasite (LGS) and langatate (LGT) doped with Eu3+ were investigated. The fluorescence lifetimes of 5D0 and 5D1 excited levels are measured. The spectroscopic figures of merit R0, R2 (the areas of the electric-dipole transitions 5D0 → 7F0 and, respectively, 5D0 → 7F2 divided by the area of the magnetic-dipole one – 5D0 → 7F1) and the maximum splitting of the 7F1 level (ΔE) are calculated from the luminescence spectra. The spectral overlapping between the luminescence from 5D0 and 5D1 levels was eliminated using pulsed excitation at 532 nm and suitable delays. We obtained R0(LGS) > R0(LGT), R2(LGS) < R2(LGT) and ΔE (LGS) > ΔE (LGS). Possible reasons (covalency, J-mixing effects) for these inequalities are discussed.