Trap‐Engineered LiCaBO 3 :Pr 3+ Phosphor for Solar‐Blind Ultraviolet Luminescence and Reversible Photochromism

Multifunctional phosphors that integrate background‐free ultraviolet‐C (UVC) persistent luminescence with rewritable optical memory are highly desirable for smart photonic applications. However, achieving such systems remains challenging, as it requires the integration of long‐lived carrier storage and reversible photochromic switching within a single defect landscape. Here, we report a single‐activator multifunctional phosphor, LiCaBO 3 :Pr 3+ (LCBO:Pr), which couples multi‐responsive UVC luminescence with reversible photochromism. Under 248 nm excitation, LCBO:Pr exhibits intense UVC down‐shifting emission (276 nm). Remarkably, the same Pr 3+ centers also enable anti‐Stokes UVC emission under 450 nm excitation, allowing blue‐light‐driven UVC output. Beyond X‐ray‐excited radioluminescence, LCBO:Pr demonstrates efficient energy storage and releases dual‐channel UVC/red persistent luminescence (>24 h) after excitation ceases. This process is accompanied by a reversible white‐to‐brown photochromic transition with a high coloration degree of 61.2%, which can be nearly completely erased by heating or blue‐light bleaching, achieving recovery efficiencies of 98.7% and 97.1%, respectively. Experimental analyses and first‐principles calculations reveal that defect states associated with V O3 and B i govern both carrier trapping and color‐center formation. The coupling of these defect‐mediated processes enables integrated optical functionalities within a single material platform, allowing multichannel information writing, readout, and erasure, and offering a versatile platform for solar‐blind photonic applications.