Structural and photoluminescence behavior of thermally stable Eu3+ activated CaWO4 nanophosphors via Li+ incorporation

Abstract

Lanthanide ion doped inorganic nanocrystals featured great attention due to their unique optical property and it can be employed to make optoelectronic devices. Metal tungstates and its derivatives are (RWO4, R = Ca, Sr, Ba) excellent host materials in various optical application. In this work, we have studied the structural and photo physical analogue of Eu3+ activated CaWO4 nanophosphors via Lithium (Li+ = 2, 5, 7 and 10 at.%) ion incorporation. As-prepared (APS) samples were annealed at 900 oC to eliminate unwanted organic moieties present in the sample and to improve crystallinity. The samples are characterized employing X-ray diffraction (XRD), Fourier transform IR spectroscopy (FTIR), UV-VIS spectroscopy, photoluminescence studies and lifetime decay studies. FTIR features an absorption band at ~832 cm-1, which correspond to its antisymmetric vibrations into O-W-O band in the WO42- tetrahedron. CaWO4 having the scheelite type structure with C4h point group and I41/a space group. The surface morphology of the samples are studied with Scanning Electron Microscopy (SEM). Lithium Co-doped CaWO4:Eu3+ nanoparticles show red luminescence because of strong host contribution and different energy transfer rates from host to Eu3+ ions under 266 nm excitations. Lithium ion enhances the crystallinity and radiative transition rate thus results in higher emissive property. Calculated CIE coordinates of these Li+ doped 900 oC annealed samples under 266 nm excitation is x = 0.65 & y = 0.34, which are closer to the standard of NTSC (x = 0.67 & y = 0.33). This material may be potential candidates for white light emitting diodes.