Photoluminescence properties of Eu(3+)-doped glaserite-type orthovanadates CsK(2)Gd[VO(4)](2)

Undoped and Eu(3+)-doped glaserite-type orthovanadates CsK2Gd1-xEux[VO4]2 with various Eu(3+) concentrations of x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 were synthesized via the solid-state reaction. The formation of a single phase compound was verified through the X-ray diffraction studies. The photoluminescence (PL) and PL excitation (PLE) spectra, PL decay curves, and absolute quantum efficiency (QE) were investigated. Unlike the conventional Eu(3+)-doped vanadates, these Eu(3+)-doped samples showed not only several sharp emission lines due to Eu(3+) but also a broad emission band with a maximum at 530 nm due to the [VO4](3-) host. The intensities of the host and Eu(3+) emissions increased when the Eu(3+) concentration was increased from x = 0 to x = 0.6 and decreased above x = 0.6. Similar concentration dependence was observed for QE. The host emission, even if in the Eu(3+)-condensed host of CsK2Eu(VO4), was never quenched indicating inefficient energy transfer from the host [VO4](3-) to Eu(3+). This inefficient energy transfer is understood by suppression of the energy transfer by the V-O-Eu bond angle deviated from 180° and the separation of Eu(3+) ions at the Gd(3+) site from [VO4](3-). Like the 530 nm charge transfer [VO4](3-) emission, two broad and intense PLE bands with maxima at 330 and 312 nm were observed for the Eu(3+) emission. A maximum QE of 38.5% was obtained from CsK2Gd1-xEux[VO4]2 (x = 0.6). A white-colored emission was obtained by the combination of the broad 530 nm emission band and the intense sharp lines due to Eu(3+) at 590-620 nm.