Structural and optical properties of langbeinite-related red-emitting K 2 Sc 2 (MoO 4 )(PO 4 ) 2 :Eu phosphors.

The concentration series of langbeinite-related solid solutions K 2 Sc 2 (MoO 4 )(PO 4 ) 2 : x Eu ( x = 0.1, 0.2, 0.6, 0.8, and 1.0 mol%) has been prepared via a solid state route and the effects of europium content on the phase composition, morphology, crystal structure and luminescence properties have been studied by scanning electron microscopy, X-ray powder diffraction, UV-vis, IR and luminescence spectroscopy. The band gap values have been estimated from UV-vis spectra and are in the range of 3.7-3.8 eV for all concentrations studied. The electronic band structure calculations have shown that Sc d, Mo d and O phos p states dominate in the band edge region and determine the optical transitions in the K 2 Sc 2 (MoO 4 )(PO 4 ) 2 host. The photoluminescence (PL) spectra, intensity and decay time dependences on the Eu 3+ concentration revealed complex behavior of europium-containing emitting centers. The PL characteristics indicated the presence of at least two types of luminescence centers. One of them (Eu K ) is shown to be formed by the Eu 3+ ion located within K sites, while the other one is formed by the Eu 3+ ions that reside in Sc sites (Eu Sc ). The luminescence color coordinates calculated for K 2 Sc 2 (MoO 4 )(PO 4 ) 2 : x Eu indicated that these ceramics can be potential candidates for UV-based lighting applications as efficient red phosphors.