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Title: Inorganic Molecular Ruby sensor: Cr³⁺-Anderson Polyoxometalate for Optical Thermometry and Manometry under extreme conditions of Temperature and Pressure

Authors: Ch. Hernández-Álvarez, D. Prętka, V. Patroniak, P. Woźny, A. Gorczyński, N. Vadra, L. Marciniak, M. Runowski

Journal: Laser & Photonics Reviews

DOI: 10.1002/lpor.71575

The understanding of temperature-pressure cross-talks is crucial for the development of reliable bi-functional optical thermometers-manometers operating under extreme conditions. Here we evidenced for the first time the dependence of the sensor's pressure sensitivity on the temperature of the system and vice versa. We show that a chromium(III) Anderson polyoxometalate (Cr-POM) acts as a solution-processable “inorganic molecular ruby”-a discrete, modular cluster that emulates ruby-like Cr³⁺ photophysics while enabling bottom-up chemical programmability. Under 375 nm excitation, Cr³⁺ emission was recorded from 93-413 K and 0-7.96 GPa using a diamond anvil cell setup. The luminescence showed a progressive redshift with increasing temperature and pressure, which was empirically modeled through linear and quadratic relations, respectively. When both variables were considered simultaneously, a 3D surface fitting approach was used to describe the interdependent behavior of the emission peak. The obtained pressure shift rate (1.43 nm·GPa⁻¹) exceeds four times that of the standard ruby sensor, highlighting much higher sensitivity of the developed molecular sensor material within the low-to-moderate pressure regime. These results establish Anderson-type Cr-POMs as a versatile, modular platform for dual pressure-temperature sensing with superior sensitivity, thus overcoming limitations of inorganic ruby crystals and outperforming typical organic molecular sensors in robustness and stability.