Modulating multi-color room temperature phosphorescence emission for carbon dot composites with ultralong lifetime

As new luminescent materials, room temperature phosphorescent (RTP) carbon dots (CDs) are widely used in bioimaging, theranostics, anti-counterfeiting encryption, optoelectronic devices, etc. However, the synthesis of RTP CDs with multi-color and high quantum yield (QY) remains a major challenge. Herein, a strategy is designed and developed to synthesize metal-free multi-color (blue, green, yellow, and brown) RTP CDs within a B2O3 matrix via pyrolysis of boric acid and adipic acid. A long lifetime of 901.4 nm and a high quantum yield of 34.2% have been achieved, and their RTP can be observed by the naked eye for similar to 9 s. The structural characterization indicates that the highly rigid B2O3 matrix and covalent network structure with C (sic) O, B-C, C-O, and C-O-B efficiently suppress non-radiative recombination by locking the triplet excitons. More importantly, the phosphorescent color of CDs can be regulated efficiently by the degree of oxidation and carbonization. These excellent optical properties allow CDs to be more applicable in anti-counterfeiting encryption, information protection, and bioimaging. This discovery will facilitate understanding the luminescence mechanism of multi-color RTP CDs and expand their practical applications.