High-sensitive temperature sensing based on thermal-enhanced emission and non-thermally coupled energy levels of white upconversion luminescence system

Na₃Y(VO₄)₂:Nd³⁺,Yb³⁺,Ho³⁺,Tm³⁺ phosphors present significantly improved sensitivity of optical temperature sensing based on thermal-enhanced upconversion luminescence and non-thermally coupled energy levels. Under 808 nm excitation, white upconversion luminescence is successfully achieved in Nd³⁺-sensitized system. In addition, the emissions intensities originated from ⁴G_5/2→⁴I_9/2 transition of Nd³⁺ and ³F_2,3→³H₆ transition of Tm³⁺ gradually increase with elevating temperature owning to the thermal population effects, as opposed to the blue (¹G₄→³H₆ transition of Tm³⁺), green (⁵S₂,⁵F₄→⁵I₈ transition of Ho³⁺) and red (⁵F₅→⁵I₈ transition of Ho³⁺) emissions intensities show continuous decreasing trend. The temperature sensing behaviors are investigated by employing multiple non-thermally coupled energy levels. Based on non-thermally coupled energy levels of ⁴G_5/2 (Nd³⁺)/¹G₄ (Tm³⁺), the absolute and relative sensitivities are obtained to be 0.433 K⁻¹ and 2.81 % K⁻¹. These results demonstrate that the Na₃Y(VO₄)₂:Nd³⁺,Yb³⁺,Ho³⁺,Tm³⁺ phosphors with superior optical thermometry performance and white luminescence within a relatively wide temperature range can achieve optical applications in many fields.