High‐yield upcycling of feather wastes into solid‐state ultra‐long phosphorescence carbon dots for advanced anticounterfeiting and information encryption.

Recently, biomass‐derived carbon dots (CDs) have attracted considerable attention in high‐technology fields due to their prominent merits, including brilliant luminescence, superior biocompatibility, and low toxicity. However, most of the biomass‐derived CDs only show bright fluorescence in diluted solution because of aggregation‐induced quenching effect, hence cannot exhibit solid‐state long‐lived room‐temperature phosphorescence (RTP) in ambient conditions. Herein, matrix‐free solid‐state RTP with an average lifetime of 0.50 s is realized in the CDs synthesized by one‐pot hydrothermal treatment of duck feather waste powder. To further enhance RTP lifetime, hydrogen bonding is introduced by employing polyols like polyvinyl alcohol (PVA) and phytic acid (PA), and a bimodal luminescent CDs/PVA/PA ink is exploited by mixing the CDs and polyols. Astonishingly, the CDs/PVA/PA ink screen‐printed onto cellulosic substrates exhibits unprecedented green RTP with average lifetime of up to 1.97 s, and the afterglow lasts for more than 14 s after removing UV lamp. Such improvement on RTP is proposed to the populated excited triplet excitons stabilized by rigid chains. Furthermore, the CDs/PVA/PA ink demonstrates excellent potential in anticounterfeiting and information encryption. To the best of the authors' knowledge, this work is the first successful attempt to fabricate matrix‐free ultra‐long RTP CDs by reclamation of the feather wastes for environmental sustainability. [ABSTRACT FROM AUTHOR]