Efficient upconversion emission and high-sensitivity thermometry of BaIn2O4:Yb3+/Tm3+/RE3+ (RE = Er3+, Ho3+) phosphor

BaIn2O4:Yb3+/Tm3+/RE3+ (RE = Er3+, Ho3+) upconversion (UC) phosphors were synthesized via the sol-gel method. Rietveld refinement based on XRD data proved that In3+ ions were replaced by rare earth (RE) ions. Under 980 nm excitation, UC and optical temperature-sensing properties were investigated, and the results indicated that the samples demonstrated high UC emission efficiencies and bright emission visible to the naked eye. The luminescence intensity ratio (LIR) technology based on thermally and non-thermally coupled levels was applied to study the optical temperature-sensing properties of the RE-doped BaIn2O4 phosphors. For the BaIn2O4:Yb3+/Tm3+/Er3+ phosphor, the absolute sensitivity reached a maximum value of 0.1433 K-1 at 473 K, which was based on the non-thermally coupled levels (non-TCLs) of (1)G(4) (blue luminescence at 480 nm of Tm3+ ion) and H-2(11/2) (green luminescence at 525 nm of Er3+ ion). For the BaIn2O4:Yb3+/Tm3+/Ho3+ phosphor, the maximum absolute sensitivity was 0.2545 K-1, which came from the non-TCLs of H-3(4) (infrared luminescence at 795 nm of Tm3+ ion) and (1)G(4) (blue luminescence at 480 nm of Tm3+ ion). BaIn2O4:Yb3+/Tm3+/RE3+ (RE = Er3+, Ho3+) samples were proven to have excellent optical temperature-sensing properties and could be applied to design optical thermometry.