Effect of processing parameters on NaGdYF4:Yb,Er UCNPs structural, morphological and optical properties

Abstract

Synthesis of monosized and spherical Up-Converting NanoParticles (UCNPs) with biocompatible surface are of a great interest because of their potential application in biomedicine as biomarkers or drug delivery systems. Among different synthesis routes reported in the literature, a hydro/solvo thermal method is consider to be most potential one for scaling-up due fact that is simple and economically cost-effective. In this work the synthesis of NaY0.65Gd0.15F4:Yb,Er UCNPs were performed through chitosan assistant solvothermal synthesis at 200oC. Variation of precursors concentration, type of solvent and synthesis time were performed in order to explore their influence on the structural, morphological and optical properties of the UCNPs. The XRD analysis showed that with a smaller surplus of fluoride ions the formation of Y0.65Gd0.15F4:Yb,Er orthorhombic phase occurs, while the increase of fluoride content or reaction time leads to NaY0.65Gd0.15F4:Yb,Er cubic phase formation. Along with it, the changes of UCNPs morphology from spindle to spherical shape is detected. All samples emitintense green emission due to the (2H11/2, 4S3/2) → 4I15/2electronic transitions, after been excited with infrared light (λ=978 nm).