Highly sensitive ratiometric luminescence manometers based on the multisite emission of Cr3+

Abstract

Luminescent materials have been extensively utilized for remote pressure measurement via luminescence manometry for a few decades. However, the drive to enhance the precision of these measurements, while maintaining high sensitivity to pressure changes, necessitates the exploration of new strategies and materials that meet these requirements. A ratiometric pressure readout based on the broadband Cr³⁺ emission, associated with the ⁴T₂ → ⁴A₂ electronic transition, addresses these needs by enabling both the accurate readout and imaging of pressure changes with extremely low thermal susceptibility. This paper demonstrates, for the first time, that employing a material with two crystallographic sites occupied by Cr³⁺ ions in MgGeO₃:Cr³⁺ allows for multimodal pressure readings that can be tailored to different measurement conditions. The simultaneous blueshift of both ⁴T₂ → ⁴A₂ emission bands of Cr³⁺ ions with increasing pressure results in changes in the spectral position and shape of the emission band of MgGeO₃:Cr³⁺. The intensity ratio of these two bands can be employed for ratiometric readout with a relative sensitivity (S_R,p) reaching ca. 22% GPa⁻¹. Furthermore, as we have shown, utilizing the ratio of emission intensities within the defined spectral ranges not only significantly increases the relative manometric sensitivity to S_R,p = 62% GPa⁻¹, but also simplifies the measurement methodology. Additionally, by carefully selecting the luminescence intensity ratio, it is possible to achieve high insensitivity to temperature changes, with the thermal invariability manometric factor (TIMF) reaching 600 K GPa⁻¹. The conducted studies clearly indicate the high application potential of the MgGeO₃:Cr³⁺ material in luminescence manometry and confirm that the approach based on the ratio of the relevant spectral ranges offers more favorable manometric performance compared to the approach based on deconvolution of the emission spectra.