Structural and photoluminescence properties of thermally stable Eu3+activated CaWO4 nanophosphor via Li+ incorporation

Abstract

In the present paper, we have reported the variation of CaWO4:Eu3+ nano phosphors with different compositions of Li+, (LEC) (Li+ = 2, 5, 7 and 10 at%). The as-prepared (ASP) samples are annealed at 900 °C to eliminate unwanted organic moieties present in the sample and to improve crystallinity. These nanoparticles are characterized by X-ray diffraction (XRD), Thermogravimetric Analysis (TGA), X-ray photoelectron spectroscopy (XPS), Fourier transform IR spectroscopy (FTIR), Raman spectroscopy, photoluminescence studies. FTIR gives the absorption band at ~832 cm−1, which corresponds to antisymmetric vibrations due to O-W-O band in the WO42- tetrahedron. This is also confirmed by the Raman Spectroscopy. CaWO4 has a crystal of the Scheelite type having C4 h point group symmetry and I41/a space group symmetry. The surface/ particle morphology of 900 °C annealed samples studied using Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) and show the formation of nanosheet like structure. Annealed samples of lithium co-doped CaWO4:Eu3+nanoparticles have shown the red luminescence which is attributed due to the strong host contribution and different energy transfers from Li+ ions to host matrix under 392 nm excitations. Li+ ion improves the crystallinity and radiative transition rate and these materials may be potential candidates for white light emitting diodes and may be widely used as optoelectronic materials.