Synthesis and luminescent properties of Tb~(3+) activated AWO_4 based (A = Ca and Sr) efficient green emitting phosphors

摘要

Optically efficient terbium activated alkaline earth metal tungstate nano phosphors (AWO_4 [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, photolu-minescence 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-0 antisymmetric stretching vibrations into the [WO_4]~(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 Tb~(3+). Under excitation of UV light, these AWO_4:xTb~(3+) (A = Ca, Sr) phosphors showed a strong emission band centered at 545 nm (green) which corresponds to ~5D_4 → ~7F_5 transition of Tb~(3+). Analysis of the emission spectra with different Tb~(3+) concentrations revealed that the optimum dopant concentration for CaWO_4:xTb~(3+) and SrWO_4:xTb~(3+) phosphors are about 8 and 6 mol% of Tb~(3+). The green emission intensity of the solid state meta-thesis prepared CaWO_4:0.08Tb~(3+) and SrWO_4:0.06Tb~(3+) phosphors are 1.5 and 1.2 times greater than that of the commercial LaPO_4:Ce, Tb green phosphor. All properties show that AWO_4:Tb~(3+) (A = Ca, Sr) is a very appropriate green-emitting phosphor for fluorescent lamp applications.