High‐Electric Field Ultraviolet‐C Electroluminescence from LuPO₄:Bi³⁺ Film on Silicon Substrate

Lutetium orthophosphate (LuPO 4 ) film has been developed by an all‐solution process sol–gel spin coating method on a silicon substrate. The film is activated by Bi 3+ ions that are utilized for an electroluminescent (EL) device. The film is annealed in optimum temperature and Bi 3+ concentration and formed as a tetragonal single‐phase LuPO 4 crystal, which has been confirmed by crystallographic analysis. A thin Au is utilized as a transparent electrode and integrated into the device. Thereby, under high‐electric field excitation, the EL device emits an ultraviolet‐C (UVC) spectrum with an emission center at 238 nm, which is optically attributed to the A‐band transition of Bi 3+ ions. Further optical and electro‐optical properties are investigated, and the results are comprehensively examined. This demonstration of Bi 3+ ‐doped LuPO 4 presents a maiden realization of the environmentally friendly UVC‐emitting device based on orthophosphate film on silicon photonics and will pave the way for the advanced development of mercury‐free UV sources based on thin‐film EL.