Spectroscopic characterization of ligands on the surface of water dispersible NaGdF4:Ln3+ nanocrystals

► Spectroscopic properties of NaGdF4:Eu3+(Er3+) nanoparticles are systematically studied. ► Fluorescence as a reliable tool for determination of the species present on the NC's surface. ► The NOBF4 treatment removes effectively the oleate ligands from the surface of NCs. ► Only the synthesis of NaGdF4 in inorganic medium yields the organic ligand-free sample.