Temperature sensing behavior in Yb³⁺–Tb³⁺ and Eu³⁺ doped Ca₂Gd₈(SiO₄)₆O₂ phosphors based on upconversion and downshifting luminescence

Abstract

To develop new phosphor materials for optical temperature sensing application, a series of Yb³⁺–Tb³⁺ and Eu³⁺ doped Ca₂Gd₈(SiO₄)₆O₂ (CGS) phosphors were designed by solid-state reaction method. Upon 980 nm excitation, the green emission of Tb³⁺ was observed in the CGS:0.8Yb³⁺, xTb³⁺ (0.08 ≤ x ≤ 1.2) phosphors, which could be mainly owing to the cooperative energy transfer from Yb³⁺ to Tb³⁺. The corresponding upconversion (UC) luminescence mechanism was studied by using the dependence of UC emission intensity on excitation powder. The temperature-dependence indicates that the ratio of the Tb³⁺ emission intensities of I_5D4 and I_5D3 changes with temperature, which shows a linear relationship. The high absolute sensitivity was achieved to be about 0.431 K⁻¹. Upon 463 nm excitation, the Eu^{3+ 5}D_0,1–⁷F_J transitions were found in the Eu³⁺-activated CGS. The investigation on temperature-dependence reveals that with increasing temperature the intensities of ⁵D₀–⁷F_J transitions decrease but those of ⁵D₁–⁷F_J transitions increase gradually, owing to the thermally coupled ⁵D₀ and ⁵D₁ levels. The fluorescence lifetime based temperature sensing properties was studied in this sample.