Phosphor-Assisted Temperature Sensing and Imaging Using Resonant and Nonresonant Photoexcitation Scheme

Phosphor-assisted luminescent thermometry relies on studying, often subtle, temperature-dependent spectral properties, such as luminescence spectra, bands shifts, or luminescence lifetimes. Although this is feasible with high-resolution spectrometers or time-resolved detectors, technical implementation of such temperature mapping or wide-field imaging is complex and cumbersome. Therefore, a new approach for noncontact ratiometric temperature detection has been proposed based on comparison of emission properties of bright Cr³⁺-doped phosphors at single emission band upon two, resonant and nonresonant, optical excitation bands. The proposed method of temperature readout was examined for three different host materials: YAlO₃, Y₃Al₅O₁₂, and LiLaP₄O₁₂ nanocrystals. The highest relative sensitivity in physiological temperature range was found for YAlO₃ nanocrystals reaching 0.35%/K, which is related to the highest crystal field found for this phosphor. The proposed methodology and the obtained materials enabled to not only reliably measure temperature in the range of -150 to 300 °C but also significantly simplify the technical detection scheme. In consequence, lamp-photoexcited, wide-field, micron-resolution microscopy imaging became possible, which is of special interest for many remote temperature studies in technology and biomedical applications.