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

Abstract

BaIn₂O₄:Yb³⁺/Tm³⁺/RE³⁺ (RE = Er³⁺, Ho³⁺) upconversion (UC) phosphors were synthesized <i>via</i> 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 ¹G₄ (blue luminescence at 480 nm of Tm³⁺ ion) and ²H_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 ³H₄ (infrared luminescence at 795 nm of Tm³⁺ ion) and ¹G₄ (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.