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The orthovanadate poly-crystals K3RE(VO4)2 (RE = La, Pr, Eu, Gd, Dy, Y) were synthesized via the solid-state reaction route. The crystal phase formation was verified through X-ray diffraction (XRD) studies and was performed by structural refinements. The optical properties were also investigated in detail. K3RE(VO4)2 (RE = Eu, Dy, Gd, Pr, La, Y) phosphors present different luminescence behaviors: the profiles of excitation and emission spectra, the spectra shift, the luminescence decay lifetimes, the absolute quantum efficiency (QE), and the CIE color coordinates are very different. The luminescence of K3RE(VO4)2 (RE = La, Gd, Y, Pr) presents yellow or yellowish green color, while, K3Dy(VO4)2 and K3Eu(VO4)2 show white and red luminescence, respectively. This was discussed on the base of the different micro-structure, activator centers, and the charge transfer transitions from [VO4]3- groups in the lattices. K3Y(VO4)2 and K3Eu(VO4)2 show higher QE values of 47.0% and 45.0% at room temperature, respectively. All the phosphors have efficient absorption in the region of near-UV wavelengths or blue wavelength region. This can well match with the light from UV-LED (360-400 nm) or blue LED chips (450-480 nm) based on GaN semiconductor. K3RE(VO4)2 could be suggested to be a potential candidate to give further investigations for the application on near-UV excited white LEDs. [ABSTRACT FROM AUTHOR]

A novel reddish orange-emitting phosphor of Eu3+-doped aluminate Sr3RAl2O7.5 (R=Lu, Y) was successfully synthesized by wet-chemistry sol-gel method. The samples were characterized by X-ray powder diffraction (XRD) and scanning electron microscope (SEM). The luminescence properties such as photoluminescence excitation and emission spectra, decay curves, CIE color coordinates and luminescence quantum efficiency were investigated. This phosphor can be efficiently excited by UV and near-UV light and exhibits a bright reddish orange luminescence with the abnormally strongest 5D0→7F0 transition. Two distinct Eu3+ sites can be observed on the emission spectra under the excitation of UV light (excitation at charge transfer band of Eu3+ ions) or dye laser in the 5D0→7F0 wavelength region (selective excitation into each site). The site-selective luminescence decay curves have been investigated in the 5D0→7F0 region of each Eu3+ site by using a pulsed, tunable, and narrowband dye laser. Each Eu3+ site presents the distinct luminescence lifetime with different rise time. The Stark energy levels of two Eu3+ sites were assigned from the site-selective emission spectra. The energy transfer can happen between the closely neighbored Eu3+ sites in Sr3RAl2O7.5 (R=Lu, Y). The luminescence mechanism responsible for the abnormally strong 5D0→7F0 transition was discussed. [ABSTRACT FROM AUTHOR]

CdS/reduced graphene oxide composites were synthesized by a simple one-pot combustion method using cadmium nitrate, thiourea and graphite as raw materials. The structure, morphologies, and photocatalytic properties of the as-prepared samples were studied by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, photoluminescence and ultraviolet-visible spectrophotometry. The results show that the structure of CdS in as-prepared samples changes from hexagonal to cubic phase by increasing the added amount of graphene oxide. During combustion reaction, graphene oxide was reduced to reduced graphene oxide. As-obtained CdS/reduced graphene oxide composites show high visible-light photoactivities, attributed to the minimized recombination of photoinduced electrons and holes and the high surface area of reduced graphene oxide sheets. [ABSTRACT FROM AUTHOR]

Undoped and Eu3+-doped glaserite-type orthovanadates CsK2Gd1-xEux[VO4]2 with various Eu3+ 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 Eu3+-doped vanadates, these Eu3+-doped samples showed not only several sharp emission lines due to Eu3+ but also a broad emission band with a maximum at 530 nm due to the [VO4]3- host. The intensities of the host and Eu3+ emissions increased when the Eu3+ 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 Eu3+-condensed host of CsK2Eu(VO4), was never quenched indicating inefficient energy transfer from the host [VO4]3- to Eu3+. 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 Eu3+ ions at the Gd3+ 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 Eu3+ 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 Eu3+ at 590-620 nm. [ABSTRACT FROM AUTHOR]