A new method to synthesize Sub-10 nm CaF2: Nd3+ nanoparticles and fluorescent enhancement via Li+ ions or Ce3+ ions doping. (April 2020) - Wang, Tan
Abstract: In this contribution, we provided a new, simple, cheap, repeatable and easily tunable method to synthesize CaF2 :Nd 3+ NPs using coprecipitation strategy. By controlling reaction time, temperature and solute/solvent, CaF2 :Nd 3+ NPs with dimeters ranging from 2.2–4.6 nm were synthesized. Then we optimized the Nd 3+ concentration and found CaF2 :6Nd(mol%) NPs with strongest luminescence. Furthermore, to further enhance the fluorescence of the optimized NPs, we explored both Li + doping and Ce 3+ doping to afford highly fluorescent CaF2 :Nd 3+ NPs. For Li + doping CaF2 :6Nd, xLi(mol%) NPs, under the excitation of 800 nm, a ~4-fold fluorescence enhancement was observed, while for Ce 3+ doping CaF2 :6Nd, xCe(mol%) NPs, a 10.4-fold fluorescence enhancement was observed. Li + doping leads to two fluorescence maxima at 4% and 30%, mainly dominated by charge compensation, and increased crystallity/grain size, separately. As comparison, Ce 3+ doping resulted in the monotonical increase of the fluorescence, dominated by lowered crystal symmetry, changed local crystal field and dissociated Nd 3+ - Nd 3+ clusters. Highlights: A new method from Ca(OH)2 /OA(oleic acid)/NH4 F reagent was proposed to synthesize CaF2 NPs. Ce 3+ doped CaF2 :Nd 3+ NPs exhibited a 10.9 times stronger photoluminescence than that of non-doped NPs. The mechanism to change crystal symmetry and break Nd3+ cluster to enhance photoluminescence by Ce3+ doping is effective.