Facile synthesis of accordion-like Y2O3:Er3+ nanothermometers for ratiometric temperature sensing applications

Non-contact thermometry operating at the sub-micrometer level based on self-referencing upconversion (UC) micro-nanomaterial is an attractive pursuit for optical thermometers. Here, a novel accordion-like Y2O3:Er3+ nanothermometer with green/red UC luminescence is obtained from the solvent-free grinding and the following temperature-programmed calcination of the Er3+-doped Y-containing metal-organic framework (MOF) precursor. Upon 980 nm laser irradiation, the as-prepared Y2O3:Er3+ exhibits dual-emitting green and red emissions originating from Er3+ ions with a two-photon UC process, and the intensities are strongly dependent on temperature. The optical thermometry behaviours of Y2O3:Er3+ nanothermometer using the fluorescence intensity ratio (FIR) technique are studied in the temperature range of 298–393 K within the physiological temperature, in which the thermally coupled levels of two green emissions and another pair of coupled levels with red and green emissions are comparatively investigated. A relative large calculated energy gap ΔE (951 cm−1) for the thermally couple levels of 2H11/2 and 4S3/2 and a maximum absolute sensitivity (Sa) of 0.0027 K−1 at 393 K are determined, respectively. This novel accordion-like Y2O3:Er3+ nanothermometer exhibits excellent optical sensing stability and high temperature resolution, demonstrating its great potential as reliable and promising optical thermometers.