Efficient upconversion emission and high-sensitivity thermometry of BaInO:Yb/Tm/RE (RE = Er, Ho) phosphor

BaIn 2 O 4 :Yb 3+ /Tm 3+ /RE 3+ (RE = Er 3+ , Ho 3+ ) upconversion (UC) phosphors were synthesized via the sol-gel method. Rietveld refinement based on XRD data proved that In 3+ 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 BaIn 2 O 4 phosphors. For the BaIn 2 O 4 :Yb 3+ /Tm 3+ /Er 3+ 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 Tm 3+ ion) and 2 H 11/2 (green luminescence at 525 nm of Er 3+ ion). For the BaIn 2 O 4 :Yb 3+ /Tm 3+ /Ho 3+ phosphor, the maximum absolute sensitivity was 0.2545 K −1 , which came from the non-TCLs of 3 H 4 (infrared luminescence at 795 nm of Tm 3+ ion) and 1 G 4 (blue luminescence at 480 nm of Tm 3+ ion). BaIn 2 O 4 :Yb 3+ /Tm 3+ /RE 3+ (RE = Er 3+ , Ho 3+ ) samples were proven to have excellent optical temperature-sensing properties and could be applied to design optical thermometry. The absolute sensitivity for temperature sensing reaches a maximum value of 0.1433 K −1 at 473 K for BaIn 2 O 4 :Yb 3+ /Tm 3+ /Er 3+ materials.