Bi3+-enhanced upconversion luminescence and photothermal conversion performance of NaYbF4:Tm3+ nanomaterials

Non-rare earth ion-activated Yb 3+ -rich fluoride matrix luminescent materials exhibit higher absorption efficiency under near-infrared (NIR) laser excitation, and are more suitable for upconversion (UC) photoluminescence and optical heating applications. These materials are highly promising fluorescent self-labeling nano-heaters. In this work, Bi 3+ -codoped β-NaYbF 4 :Tm 3+ UC nanomaterials were synthesized by combining the hydrothermal reaction with the molten salt method. The effects of Bi 3+ doping on the crystalline phase composition, micromorphology, upconversion luminescence (UCL) properties, spectral characteristics , and optical heating performance of the synthesized materials were investigated in detail. The co-doping of 5–20 mol% Bi 3+ was found to significantly enhance the near-infrared (NIR) UCL intensity of NaYbF 4 : Tm 3+ . In particular, t he sample doped with 15 mol% Bi 3+ emitted nearly pure 801 nm monochromatic near-infrared light under 980 nm optical excitation , and its I NIR /I Blue ratio increased dramatically from 0.97 without Bi 3+ doping to 1599. This material exhibited efficient photothermal conversion capability, and the center temperature of the sample can reach ∼147.6  °C under 10 s laser irradiation, achieving a high photothermal conversion efficiency of 129.53 °C W −1 , together with excellent photothermal conversion stability. The mechanism behind the enhanced NIR emission of Bi 3+ -doped nanomaterials was also elucidated based on the energy level transition strategy.