Lanthanide-doped bismuth-based fluoride nanoparticles: controlled synthesis and ratiometric temperature sensing

Abstract

Bismuth-based nanoparticles, particularly NaBiF₄, have attracted extensive attention as hosts for lanthanides (Ln³⁺) ions and other luminescent ions in recent years. However, the controllable synthesis of NaBiF₄ nanoparticles remains a challenge. Herein, different concentrations of Gd³⁺ ion-doped NaBiF₄:Yb³⁺/Er³⁺ upconversion nanoparticles (UCNPs) have been successfully synthesized via a facile solvothermal method. By changing the doping levels of Gd³⁺ ions (0–20%), the size of NaBiF₄:Yb³⁺/Er³⁺ UCNPs can be easily tuned from 200 nm to 50 nm, but the nanoparticles always maintained the hexagonal phase structure. Under 980 nm excitation, the as-synthesized NaBiF₄:Yb³⁺/Er³⁺/20%Gd³⁺ UCNPs showed desirable luminescent properties. Furthermore, the 980 nm excited luminescence temperature-sensing behavior of NaBiF₄:Yb³⁺/Er³⁺/20%Gd³⁺ UCNPs was achieved in a wide temperature range from 148 K to 498 K. These results provide strong evidence for the controllable synthesis of NaBiF₄ UCNPs and their application in ratiometric temperature sensing.