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

Bismuth-based nanoparticles, particularly NaBiF4 , have attracted extensive attention as hosts for lanthanides (Ln(3+)) 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+/Er(3+ )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.