Visible light-excitable carbon dots@dehydrated boric acid composites with dual-mode emission for multilevel...

Carbon dots (CDs)-based composites with multicolor persistent afterglow have exhibited promising applications in advanced anti-counterfeiting, information encryption, intelligent sensing and bio-imaging. However, dual-mode emission of room temperature phosphorescence (RTP) and thermal activated delayed fluorescence (TADF) has been scarcely observed simultaneously for the single CDs-derived composites. Herein, three composites with N-doped CDs in situ anchored in dehydrated boric acid (DBA) matrix, BTA'-CDs@DBA, BTA-CDs@DBA and TA-CDs@DBA, have been developed by one-step pyrolysis of boric acid and benzotriazole-5-carboxylic acid (BTA'), 1H-benzotriazole (BTA) or 1,2,4-triazole (TA). Both the BTA'-CDs@DBA and BTA-CDs@DBA samples with comparable strong π → π^⁎ and n → π^⁎ transitions emit unusual dual-state emission of RTP and TADF under UV- and visible-light excitations with prolong emission lifetime up to 1374 and 690 ms. By contrast, the TA-CDs@DBA emitter with ignorable n → π^⁎ transition exhibits only excitation-dependent RTP emissions with slightly shortened lifetime of 1313 ms at 448 nm. Thus, as compared to TA-CDs@DBA, the N-heterocyclic carbon sources with extended conjugated skeleton and appended carboxylic group have more preferably activated the emission pathway of TADF under visible light excitation. Furthermore, benefiting from the excitation-regulated afterglow with variable duration time and emission color, these composites show intriguing applications in bicolor display, digital anti-counterfeiting and three-level information encryption.