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

Abstract

A series of polycrystalline Li3Ba2La3−xEux(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 Wopt−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.