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Abstract: The search for material hosts being able to incorporate Er3+ impurities with a thermally stable structure and a high melting temperature is priority in optical thermometry. In this work, we report on the structural and spectroscopic characterization of Er3+-doped and Yb3+/Er3+-codoped LaGdO3 nanocrystals synthesized via the sol?gel Pechini method. X-ray diffraction and Raman spectroscopy unequivocally show that the synthesis method provides nanocrystals with a single-phase B-type monoclinic structure (space group, C2/m). Intensity decay curves, I(t), were measured to investigate the efficiency of upconversion processes yielding green emission. We showed that an energy transfer upconversion (ETU) process involving Yb?Er pairs governs visible emission upon near-infrared (NIR) excitation. The temperature dependence of the thermalized green luminescence at 525 nm (2H11/2 ? 4I15/2) and 549 nm (4S3/2 ? 4I15/2) was checked for thermometric applications in the room temperature (RT) to 900 K range. We demonstrate that the B-type monoclinic phase of LaGdO3 is stable from low temperatures up to 900 K. Doped with Er3+, it shows suitable thermometer capabilities with a maximum sensitivity of S = 4.3 × 10?3 K?1 at 554 K and a relative sensitivity decreasing from its maximum value at 0 K to SR = 1.2 × 10?2 K?1 at 298 K. The results suggest that LaGdO3 in its B-type monoclinic phase is a promising material as a wide-range temperature sensor, without any further surface protection.

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