Excited state dynamics of Eu3+ in the partially disordered crystals La3Ga5SiO14 and La3Ga5.5Ta0.5O14

The spectroscopic properties of two partially disordered crystals, langasite (LGS) and langatate (LGT), doped with Eu3+ were investigated. The fluorescence lifetimes of the 5D0 and 5D1 excited levels are measured. The spectral overlapping between the luminescence from the 5D0 and 5D1 levels was eliminated using pulsed excitation at 532 nm and suitable delays in order to improve the precision of the calculation of the spectroscopic figures of merit R0, R2 (the areas of the electric-dipole transitions 5D0→7F0 and 5D0→7F2, respectively, divided by the area of the magnetic-dipole one—5D0→7F1). The maximum splitting of the 7F1 level (ΔE) is calculated from the luminescence spectra and the B20 crystal field parameter is determined. We obtain R0(LGS)>R0(LGT), R2(LGS)ΔE(LGT), and we discuss these results taking into account structural data, covalency and J-mixing effects.