Pure-green upconversion emission and high-sensitivity optical thermometry of Er3+-doped stoichiometric NaYb(MoO4)2

The optical temperature sensor based on fluorescence intensity ratio (FIR) offers significant advantages for rapid and non-contact temperature measurements. However, the application of optical temperature sensors is limited by the challenge of identifying advanced materials with high response sensitivity. In this study, phosphor and single-crystal states stoichiometric NaYb(MoO4)(2) with Er3+ doping were prepared by solid-state reaction method and Czochralski method, respectively, for promising optical thermometry applications. The structure of the phosphor and single-crystal state samples were investigated. High-purity upconversion (UC) emissions were achieved from stoichiometric NaYb(MoO4)(2):Er3+ samples with a maximum green-to-red ratio up to 70.3, which opens up numerous possibilities for their application as pure-green color converters. Besides, the UC emission spectra were monitored with respect to temperature, and the fluorescence intensity ratios (FIRs) of the H-2(11/2)-> I-4(15/2) and S-4(3/2)-> I-4(15/2) transitions of Er3+ ions were investigated to evaluate the optical temperature sensing behaviors of NaYb(MoO4)(2):Er3+. Importantly, the distinctions of optical temperature sensing behaviors between phosphor and single-crystal state samples were analyzed. The results suggest that stoichiometric NaYb(MoO4)(2):Er3+, especially for single-crystal state NaYb(MoO4)(2):Er3+, hold great promise as FIR-based optical temperature sensors. In addition, the results can also open up the research interests for employing stoichiometric materials and single crystal materials as optical thermometry applications.