Solvothermal synthesis of NaGdYF4:Yb,Er UCNPs with different structual, morphological and optical properties

Abstract

Up-Converting NanoParticles (UCNPs) with biocompatible surface and unique optical properties, low phonon energy (350 cm-1) and high chemical stability attract a great interest as potential biomarkers or drug delivery systems. The hydro/solvo thermal method, as one of the most economical method which do not include the use of toxic precursors, was applied here for the synthesis of NaY0.65Gd0.15F4:Yb,Er nanoparticles at 200oC. Chitosan is used as surfactant and structural directing agent. In addition, different processing parameters (precursor concentration, solvent type, and synthesis time) were applied to investigate their influence on the structural, morphological, and optical properties of UCNP. 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 emit intense green emission due to the (2H11/2, 4S3/2) → 4I15/2 electronic transitions, after been excited with infrared light (λ=978 nm).