Preparation and spectroscopic study of a water-soluble NaYF4:Yb3+/Er3+@NaGdF4 crystal particle and its application in bioimaging

Abstract

Water-soluble NaYF₄:Yb³⁺/Er³⁺@NaGdF₄ micron particles were prepared directly by the hydrothermal method. The growth mechanism and upconversion fluorescence emission property of the particles at different shell thicknesses were studied. The results showed that the fluorescence emission intensity of the core–shell particles increased by about ten times compared with that of bare core particles. The emission intensity increased with increase in the reaction time during particle preparation, which is due to dissolution of excess citrate from the surface of the particles. The problem of obtaining hydrophilic NaYF₄:Yb³⁺/Er³⁺@NaGdF₄ applied as biological MR imaging contrast agents and for UCL imaging was addressed during the preparation of the sample. Therefore, the method of preparation of the sample used in this study has important significance for applying inorganic UCNPs to the biological field.