Spectroscopic thermometry based on narrow photoluminescence (PL) lines is a rapidly developing field worthy for applications in systems under special environmental conditions of pressure and temperature [1]. Ruby is an archtype of such optical probes. However, its use is limited to the low temperature range (< 150K) mainly determined by the thermal coupling of the two R-lines (E= 29 cm-1), material stability and PL efficiency [2]. In this work we present a nobel oxide material, LaGdO3 that, besides the worth dielectric applications [3], when doping with Er3+, has the potential of a highly efficient up-conversion PL for high temperature thermometry at high pressure [4]. LaGdO3 belongs to the perovskite-type ABO3 compounds with a B-type monoclinic C2/m structure (a= 14.43 Å; b= 3.69 Å; c= 9.00 Å; and β= 100.70º) at ambient conditions [5]. It undergoes a structural phase transition to a hexagonal phase at 3 GPa yielding PL enhancement. Since the energy gap of the thermalized 2H11/2 and 4S3/2 Er3+ levels (E= 732 cm-1) is nearly constant with pressure, the intensity ratio between the emission from both states to the 4I15/2 ground state makes it suitable for high temperature applications (T > 1100 K). A study of its structure, vibrational and electronic properties will be presented and compared with the isostructural compound SmGdO3 showing a structural phase transition around 3 GPa [6]. We acknowledge finantial support from MINECO (MAT2015-69508-P, MAT2015-71070-REDC; PGC2018-101464-B-I00) and BSH Electrodomésticos España, S.A.
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