10‐ppb Trace Doping in Boron Oxide Resolves Purity Paradox for Programmable Time‐Dependent Phosphorescent Color

Abstract The development of eco‐friendly time‐dependent phosphorescent color (TDPC) materials faces a critical paradox: Boron oxide (B 2 O 3 ) derived from commercial boric acid (B 2 O 3 ‐ CBA ) exhibits stable room‐temperature phosphorescence (RTP) regardless of purity, while ultrapure synthetic analogs remain non‐emissive. Here, this dilemma is resolved by engineering carbon dots (CDs) doped into B 2 O 3 ‐ CBA at ultralow concentrations (10 ppb), achieving programmable TDPC through three breakthroughs. Synergistic host‐guest confinement amplifies green RTP efficiency by an order of magnitude enhancement while activating yellow guest emission; Defect‐mediated exciton transfer extends RTP lifetimes to 304 ms, doubling B 2 O 3 ‐ CBA ; Time‐resolved chromatic evolution (Δλ = 65 nm) emerges exclusively in doped systems, enabled by bifurcated decay kinetics from dual confinement mechanisms. The CDs@B 2 O 3 exhibits remarkable stability in harsh liquids, overcoming stability barriers for encryption applications. This ppb‐level doping strategy circumvents purity debates while preserving host crystallinity—a critical advance toward scalable anti‐counterfeiting tags and bioimaging probes with programmable temporal‐color responses.