Upconverting temperature sensors with high activation energy and low pump threshold

Abstract

The structural and optical properties of Er³⁺/Yb³⁺/Mo⁶⁺-codoped aurivillius-structured Bi₂WO₆ phosphors are reported. Simultaneous substitution of Bi³⁺ and W⁶⁺ by Er³⁺/Yb³⁺ and Mo⁶⁺ ions in a codoped phosphor was explored for photoluminescence study. The green emission was enhanced with the codoping of Yb³⁺ as well as Mo⁶⁺ ions in Er³⁺:Bi₂WO₆ phosphors. In the Er³⁺/Yb³⁺/Mo⁶⁺-codoped Bi₂WO₆ phosphors, the Yb³⁺–MoO₄²⁻ dimer state transfers its energy to Er³⁺ ions and is found responsible for the enhancement. The luminescence saturation processes with increased photon density have been discussed using rate equations. The ²H_11/2 and ⁴S_3/2 energy levels of Er³⁺ ions are adapted for optical thermometry. The absolute and relative sensitivities were found with a resolution of 0.38 K at room temperature and repeatability cycles of FIR. The thermal stability has been verified with the Arrhenius equation.