Our skin and materials are constantly exposed to detrimental ultraviolet light (UV) rays from the sun. It is essential to protect our health and the life of materials by intercepting this detrimental high-energy radiation with UV absorbers. Carbon dots (CDs) with low toxicity and low cost have brought a choice for UV absorbers. However, high-efficiency absorption CDs that can achieve absorption in the full ultraviolet region have rarely been reported. Herein, we synthesized a full-band carbon dot ultraviolet absorber by expanding the CD π-conjugation domain. In addition, by encapsulating CDs in a polyurethane (PU) matrix, the absorptivity of the 5 wt % CDs@PU film in the ultraviolet region was 100%, and the transmittance reached 90% in the visible region, successfully protecting the two dyes from photodegradation. The UV shielding efficiency slightly decreased under the accelerated aging experiment of 288 h. Moreover, to remove the ultraviolet light in the light-emitting diode (LED), we applied a layer of the CD film to the surface of the LED lamp, and the results indicated that the UV light was successfully blocked by the CD film without affecting the LED luminescence performance. This study offers a valid method to evolve high-efficiency, nontoxic antiaging materials and healthy lighting devices.
Carbon dots (CDs) with ultra-broadband and time-dependent afterglow photoluminescence (PL) are pivotal for next-generation anti-counterfeiting and dynamic information encryption, yet their rational design remains a formidable challenge in terms of spectral-temporal tunability and mechanistic clarity. Herein, we propose a molecular engineering strategy to synthesize CDs@B 2 O 3 via a one-step fusion heating process, using levofloxacin and 1-pyrenylboronic acid as the carbon source precursors within a boric acid matrix. By properly modulating the electronic state distribution between the green-emitting surface states and the red-emitting core states of the CDs, we achieve full coverage of the visible spectrum from green to the near-infrared region. Mechanistic investigations reveal that the broadband afterglow arises from the synergistic delayed fluorescence (DF) of N-heterocyclic surface molecular states and large conjugated domains that activate red core states. Notably, the increased conjugation degree of the carbon core in L,P-CDs@B 2 O 3 results in a higher proportion of red-emitting states and longer afterglow time, enabling a unique color-changing afterglow that transitions from an initial green through yellow and finally to red within 1 s. The time-resolved afterglow characteristics facilitate high-capacity graphical anti-counterfeiting, demonstrating promising applications in graphical security and information storage with spatiotemporal resolution. These findings not only provide an effective approach for designing smart afterglow nanomaterials but also elucidate the structure-emission relationship in carbon-based systems, offering insights into the rational engineering of multi-modal photoluminescent materials.
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