Combined Pressure–Temperature Optical Sensing with Eu3+ luminescence in BaGeO3: Unraveling Cross-Sensitivity under Extreme Conditions

Most studies of luminescence sensors treat temperature and pressure effects independently, with their combined influence on the materials luminescence unexplored. Here, a bifunctional optical sensor based on BaGeO3:Eu3+ for combined and decoupled pressure and temperature under extreme conditions is reported. Temperature sensing was done (performed?) via the luminescence intensity ratio (LIR) of the Eu3+ 5D0→7F2 and 5D0→7F1 emission bands, while pressure was calibrated following the redshift of the 614 nm emission peak. The pressure-dependent emission spectra show a reversible spectral shift of the 614 nm emission peak with a maximum sensitivity of 0.19 nm/GPa. Combined pressure and temperature measurements, in the ranges from 93 to 623 K and ambient pressure up to 15 GPa, show spectral shifts of the emission bands with temperature-dependent increases in pressure sensitivity from 0.02 nm/GPa at 93 K up to 0.32 nm/GPa at 623 K, and with pressure-dependent increases in temperature sensitivity from -7.24 up to 1.5 (×10-2 nm/K) at 15 GPa. The cross-sensitivity analysis revealed maximum temperature interference in pressure sensing of 0.025 GPa/K across the investigated temperature and pressure. This work highlights the critical interaction of cross-dependent sensitivities, opening new opportunities for the design of luminescent materials capable of decoupling multiple extreme-environment parameters.