Synthesis and luminescent properties of Tb3+ activated AWO4 based (A = Ca and Sr) efficient green emitting phosphors

Abstract

Optically efficient terbium activated alkaline earth metal tungstate nano phosphors (AWO4 [A = Ca, Sr]) with different doping concentrations have been prepared by mechanochemically assisted solid state metathesis reaction at room temperature for the first time. The prepared phosphors were characterized by the X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), Fourier transform Raman (FT-Raman) spectroscopy, photoluminescence and diffuse reflectance spectroscopy measurements. The XRD and Raman spectra results showed that the prepared powders present a scheelite-type tetragonal structure. FTIR spectra exhibited a high absorption band situated at around 850 cm−1, which was ascribed to the W–O antisymmetric stretching vibrations into the [WO4]2− tetrahedron groups and the SEM images reveal that the particle sizes were in the range of 20–60 nm. The excitation and the emission spectra were measured to characterize the luminescent properties of the phosphors. The excitation spectrum exhibits a charge transfer broad band along with some sharp peaks from the typical 4f–4f transitions of Tb3+. Under excitation of UV light, these AWO4:xTb3+ (A = Ca, Sr) phosphors showed a strong emission band centered at 545 nm (green) which corresponds to 5 D 4 → 7 F 5 transition of Tb3+. Analysis of the emission spectra with different Tb3+ concentrations revealed that the optimum dopant concentration for CaWO4:xTb3+ and SrWO4:xTb3+ phosphors are about 8 and 6 mol% of Tb3+. The green emission intensity of the solid state meta-thesis prepared CaWO4:0.08Tb3+ and SrWO4:0.06Tb3+ phosphors are 1.5 and 1.2 times greater than that of the commercial LaPO4:Ce, Tb green phosphor. All properties show that AWO4:Tb3+ (A = Ca, Sr) is a very appropriate green-emitting phosphor for fluorescent lamp applications.