Er3+/Yb3+ co-activated YNbO4 nanocrystalline phosphors: Up-conversion luminescence under the 980 nm excitation and integrated lifetime thermometry

This paper presents the structure, morphology, optical and photoluminescent properties of erbium (1 at %) and ytterbium (2 at %) doped yttrium niobium oxide (YNbO4) as a potential temperature sensor material. Obtained powder samples of fergusonite-β-like monoclinic crystalline structure of YNbO4, confirmed by X-ray diffraction analysis, showed particles of about 1–3 μm in size. Photoluminescence emissions were detected in the visible (Vis) and near-infrared (NIR) regions after excitation at 980 nm as a result of the energy up-conversion (UC) process. The lifetime of the most intense Er³⁺ excited state ⁴S3/2 level measured at 300 K was 0.238 ms. Thermometric properties were recorded at different temperatures and analyzed for the first time using the luminescence emission decay method. The relative sensitivity decreases from 0.23 % to 0.085 % K⁻¹, by varying the temperature from 300 to 600 K, indicating a good potential of this material for lifetime-based phosphor thermometry.