Lutetium‐Induced Enhancement of Pr ³⁺ Upconversion Luminescence in Yttrium Oxybromide Toward Low‐Threshold, Blue‐Pumped Deep‐Ultraviolet Lasing

Lanthanide ion‐based upconversion is a highly promising approach for achieving deep‐ultraviolet (DUV) emission. In particular, the visible‐to‐ultraviolet upconversion process of Pr 3+ ions, which proceeds via an intermediate energy level, serves as an efficient technical approach to realize high‐efficiency DUV emission under easily accessible blue light excitation. Herein, through 5% Lu 3+ doping, we have strengthened the lattice rigidity of the tetragonal yttrium oxybromide (YOBr) host, resulting in an approximately 40% enhancement in the DUV luminescence performance of Pr 3+ . Mechanistic studies show that the enhancement is attributed to the highly suppressed non‐radiative relaxation from the 4 f 1 5 d 1 state without significant thermal ionization. Moreover, we unambiguously demonstrate the formation of broadband DUV random lasing, Fabry‐Pérot cavity lasing, and whispering‐gallery‐mode microcavity lasing by employing these efficient DUV‐emitting microcrystals as the laser gain medium. Notably, the pumping threshold is substantially reduced compared to conventional five‐photon processes utilizing Tm 3+ or Er 3+ ions. Our findings highlight the viability of enhancing the DUV luminescence intensity in oxyhalides through compositional engineering and realizing DUV lasing via blue‐pumped Pr 3+ ‐based upconversion material as a gain medium.