Excited state dynamics of Eu3+ in the partially disordered crystals La3Ga5SiO14 and La3Ga5.5Ta0.5P14

The spectroscopic properties of two partially disordered crystals, langasite (LGS) and langatate (LGT), doped with Eu3+ were investigated. The fluorescence lifetimes of the D-5(0) and D-5(1) excited levels are measured. The spectral overlapping between the luminescence from the D-5(0) and D-5(1) 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 R-0, R-2 (the areas of the electric-dipole transitions D-5(0)-> F-7(0) and D-5(0)-> F-7(2), respectively, divided by the area of the magnetic-dipole one-D-5(0)-> F-7(1)). The maximum splitting of the F-7(1) level (Delta E) is calculated from the luminescence spectra and the B-20 crystal field parameter is determined. We obtain R-0(LGS)>R-0(LGT), R-2(LGS)<R-2(LGT), and Delta E(LGS)>Delta E(LGT), and we discuss these results taking into account structural data, covalency and J-mixing effects. (C) 2007 Elsevier B.V. All rights reserved.