Effect of Solvent on the Red Luminescence of Novel Lanthanide NaEu(WO4)2 Nanophosphorfor Theranostic Applications

Investigation of the red luminescence in NaEu(WO4)(2) nanoparticles synthesized using water and ethylene glycol and its biocompatibility on HeLa cells, Escherichia coli, Staphylococcus aureus, and Candida albicans has been evaluated for the first time. The Scheelite-like pure tetragonal NaEu(WO4)(2) nanoparticles have been synthesized by a simple solvotherrnal method by using water (NaEuW I) and ethylene glycol (NaEuW II) as a reaction medium. Detailed particle size and crystal structural analysis of both samples were carried out using high resolution transmission electron microscopy and Synchrotron powder diffraction. Enhanced red fluorescence was observed on increase in calcination temperature in both samples, signifying their greater stability and increased crystallinity on thermal treatment.. The blue shift of charge transfer (CT) band in NaEuW II nanoparticles is explained by the nature of the Eu-O bond lengths obtained by Rietveld refinement using Synchrotron diffraction data. Chromaticity diagrams revealed the possibility of tuning the red emission of as-prepared and annealed samples against particle size, choice of solvent, and calcination temperature. The calculated Commission Internationale de l'Eclairage (CIE) coordinates of NaEuW II at 600 C-circle matches the CIE values of the commercial red phosphor Y2O3S:Eu3+ standards of the National Standards of Television Commission (NSTC). This indicates the potential applications of nano-NaEuW [NaEu(WO4)(2)] to generate red emission. Investigation of solvent effect on particle size dependent biocompatibility of NaEu(WO4)(2) via in vitro cytotoxicity studies showed no significant toxicity toward HeLa cells, E. coli, S. aureus, and C. albicans. More interestingly, bioimaging studies show excellent biodistribution and localization of luminescent nano-NaEuW II. Hence, our preliminary studies could demonstrate a new strategy to design nanoluminescent NaEu(WO4)(2) for theranostic applications.