Pressure‐Driven Phase Transition Unlocking Unique Eu ²⁺ Luminescence in Li ₂ SrSiO ₄ for Optical Sensing and White‐LEDs

ABSTRACT 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 Li ₂ SrSiO ₄ :3%Eu ²⁺ ,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.