RESUMO
K2Eu(PO4)(WO4) has been prepared via the high-temperature solution growth (HTSG) method using K2WO4-KPO3 molten salts as a self-flux and characterized by single-crystal X-ray diffraction analysis, IR and luminescence spectroscopy. The structure of this new compound features a 2D framework containing [EuPO6]4- layers, which are composed of zigzag chains of [EuO8]n interlinked by slightly distorted PO4 tetrahedra. Isolated WO4 tetrahedra are attached above and below these layers, leaving space for the K+ counter-cations. The photoluminescence (PL) characteristics (spectra, line intensity distribution and decay kinetics) confirm structural data concerning one distinct position for europium ions. The luminescence color coordinates suggest K2Eu(PO4)(WO4) as an efficient red phosphor for lighting applications.
RESUMO
The concentration series of langbeinite-related solid solutions K2Sc2(MoO4)(PO4)2:xEu (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 Ophos p states dominate in the band edge region and determine the optical transitions in the K2Sc2(MoO4)(PO4)2 host. The photoluminescence (PL) spectra, intensity and decay time dependences on the Eu3+ 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 (EuK) is shown to be formed by the Eu3+ ion located within K sites, while the other one is formed by the Eu3+ ions that reside in Sc sites (EuSc). The luminescence color coordinates calculated for K2Sc2(MoO4)(PO4)2:xEu indicated that these ceramics can be potential candidates for UV-based lighting applications as efficient red phosphors.
