Highly efficient upconversion emission of Er3+ in δ-Sc4Zr3O12 and broad-range temperature sensing

Abstract

Developing optical temperature sensors with a wider range, higher sensitivity and repeatability based on Er³⁺/Yb³⁺ doped upconverting phosphors has always been at the forefront of temperature measurement technologies. Here, we report the intense green upconversion luminescence in Er³⁺/Yb³⁺ doped δ-Sc₄Zr₃O₁₂ for the first time and its temperature sensing performance is investigated. The structure of δ-Sc₄Zr₃O₁₂ is given by Rietveld refinement of XRD data and the site occupancy of Er³⁺ ions has been determined. Compared with cubic Sc₂O₃ and ZrO₂, under 972 nm excitation, the green emission from Er³⁺ centers in Sc₄Zr₃O₁₂ is increased by 59-fold and 264-fold, respectively. By experimental analysis, this enhancement of upconversion luminescence is attributed to the low-symmetrical environment of Er³⁺, generation of Yb³⁺ clusters and high internal efficiency of Yb³⁺ emission in Sc₄Zr₃O₁₂. In addition, the fluorescence intensity ratio of two green emission bands (²H_11/2/⁴S_3/2 → ⁴I_15/2) is studied as a function of temperature ranging from 303 to 793 K in Sc₄Zr₃O₁₂. The maximum sensitivity observed via calculation is 0.00634 K⁻¹ at 573 K, and the sensitivity is still as high as 0.00534 K⁻¹ at 793 K. The stability of a Sc₄Zr₃O₁₂ thermometer is also examined via a recycling test. These findings suggest that δ-Sc₄Zr₃O₁₂ is a promising upconversion host and could achieve high-sensitivity optical temperature sensing with a wide measuring range.