Synthesis and optical properties of Li3Ba2La3(MoO4)8:Eu3+ powders and ceramics for pcLEDs

Abstract

A series of polycrystalline Li₃Ba₂La_3−xEu_x(MoO₄)₈ samples were prepared by the conventional solid-state reaction. The phase formation of the samples was investigated by X-ray diffraction measurements. The luminescence spectra and decay curves were studied as a function of Eu³⁺ concentration and temperature. It turned out that the optical band gap of the undoped molybdates is at 3.65 eV. The quantum efficiency (QE) of the Eu³⁺ doped luminescent materials increases with increasing Eu³⁺ concentration and almost 100% QE was obtained for those samples doped with 70, 80, or 90% Eu³⁺. A sample containing 100% Eu³⁺ showed solely a slight decrease in quantum efficiency. The luminous efficacy (LE) was 330 and 312 lm W_opt⁻¹ for the 10 and 100% Eu³⁺ doped samples, respectively. The decrease of LE values is caused by a slight shift of the colour point to the red spectral range with increasing Eu³⁺ content. Temperature dependent measurements revealed that Li₃Ba₂Eu₃(MoO₄)₈ loses only 15% of efficiency up to 400 K, which demonstrates that the investigated phosphors are attractive for application in pcLEDs.