Controlled synthesis and tuned fluorescence properties of NaGdF4:Yb, Er up-conversion nanocrystals through one-step hydrothermal approach

Abstract

The properties of NaGdF4:Yb, Er nanomaterials tuned by synthesis conditions have always been one of the research hotspots in the field of upconversion nanomaterials. In this work, NaGdF4:Yb, Er upconversion nanomaterials capped with oleic acid (OA) molecules were prepared by one-step hydrothermal method. Controlling the fluorescence properties of NaGdF4:Yb, Er nanomaterials by changing the synthesis conditions were principally investigated. The results showed that the crystalline state of the as-prepared upconversion nanomaterials tended to be intact and fluorescence emission capability enhanced when the reaction temperature increased from 140 °C to 160 °C, 180 °C and the reaction time extended from 6 h to 18 h. From 0.00 mmol to 0.75, 2.25, 5.00, 8.75, 12.50, 17.50 mmol of sodium hydroxide amount, the synthesized upconversion nanoparticles (UCNPs) transferred from orthorhombic GdF3 to hexagonal β-NaGdF4. And when the amount of sodium hydroxide was 2.25 mmol, the as-prepared nanoparticles exhibited stronger luminescence intensity. The ratio of Re3+ (Gd3+:Yb3+:Er3+) could also affect the properties of the as-prepared UCNPs. The nanomaterials emitted relatively stronger fluorescence when the ratio among Gd3+, Yb3+, Er3+ was 78:20:2. This work provides solid foundation for further theoretical study and practical application of NaGdF4:Yb, Er nanomaterials.