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

The development of eco-friendly time-dependent phosphorescent color (TDPC) materials faces a critical paradox: Boron oxide (B₂O₃) derived from commercial boric acid (B₂O₃-_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 B₂O₃-_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 B₂O₃-_CBA; Time-resolved chromatic evolution (Δλ = 65 nm) emerges exclusively in doped systems, enabled by bifurcated decay kinetics from dual confinement mechanisms. The CDs@B₂O₃ 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.