Accurate pressure measurement under extreme conditions is essential for probing structural evolution and pressure-induced phenomena in condensed-matter physics and materials science. However, conventional optical manometers often require ultraviolet excitation and face challenges such as low pressure sensitivity, high UV laser costs, and spectral interference from background fluorescence.

Now, a research team led by Prof. CHEN Xueyuan from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences (CAS), in collaboration with Prof. QUAN Zewei's group at Southern University of Science and Technology, has developed a novel class of ultrasensitive pressure-responsive upconversion luminescent manometer based on Yb³⁺/Mn²⁺ co-doped Cs₂NaBiCl₆ double perovskites.

The findings were recently published in Advanced Materials.

In this study, researchers took advantage of the soft lattice of Cs₂NaBiCl₆ to enable pressure-sensitive upconversion luminescence from Mn²⁺ through Yb³⁺ sensitization. Under 980 nm excitation, Yb³⁺ efficiently absorbs near-infrared light and transfers energy to Yb³⁺–Mn²⁺ dimers, producing yellow broadband upconversion emission centered at 586 nm. Because Mn²⁺ emission is highly susceptible to the local crystal field environment, its 3d energy levels respond sensitively to pressure-induced changes in the local crystal-field environment. The soft lattice of Cs₂NaBiCl₆ further amplifies the pressure-induced modulation of the Mn²⁺ local environment, substantially enhancing the spectral response sensitivity.

Within the pressure range of 0–7.19 GPa, the material showed a continuous redshift in its emission spectrum and clearly visible color changes. The centroid of the emission band exhibited an excellent linear response to pressure, with a sensitivity of 15.03 nm/GPa—the highest sensitivity ever reported for linearly responsive visible‑light pressure sensors.

In situ high-pressure X-ray diffraction revealed that Cs₂NaBiCl₆:Yb³⁺/Mn²⁺ maintained good structural stability during compression, with a bulk modulus of only 23.69 GPa, indicating high compressibility that underpins its exceptional pressure sensitivity. In situ Raman spectroscopy and pressure cycling tests further confirmed its excellent stability and reproducibility.

According to the researchers, this study integrates near-infrared excitation with highly sensitive pressure-responsive luminescence, offering a novel materials design strategy for high-precision optical pressure sensing.

With its linear response, high sensitivity, visual readout, and robust cycling stability, the material shows promise for precision pressure monitoring in high-pressure physics, deep-sea exploration, and simulations of conditions in Earth's and planetary interiors, the researchers said.

Schematic diagram of ultrasensitive pressure-responsive upconversion luminescent manometer based on Cs₂NaBiCl₆:Yb³⁺/Mn²⁺ double perovskite. (Image by FJIRSM)