Pressure-Driven Phase Transition Unlocking Unique Eu²⁺ Luminescence in Li₂SrSiO₄ for Optical Sensing and White-LEDs

Controlling the luminescence behavior of rare-earth-doped materials under extreme physical conditions of pressure and/or temperature is crucial for the development of next-generation solid-state lighting and optical sensors. Here, the Li₂SrSiO₄:3%Eu²⁺,0.5%Cs⁺ phosphors were synthesized and permanently modified by high-pressure treatment to design high-performance white-LED and optical manometer. With Cs⁺ introduction, the luminescence intensity, quantum efficiency, and thermal stability of the phosphors increased. Using the designed phosphor as a yellow-emitting component, a white-LED was fabricated. The studied material was also used to develop a multiparametric optical pressure and temperature sensor. Importantly, compression above 14.0 GPa induced formation of a new high-pressure β-phase, which can be recovered under ambient conditions, and - exhibits an unique pressure-induced emission band. Photoluminescence spectroscopy revealed the presence of yellow and a new blue emission component in the emission spectrum, providing sensitivities of the synthesized phosphors over 9 and 5 nm GPa^-1, respectively. Moreover, the application of high pressure in a large-format press (up to 20 GPa) enabled the fabrication of a white-LED device with improved color performance. Such large-scale, high-pressure postsynthetic treatment for the development of sensors and new light sources is reported here for the first time.