Multiple-color room-temperature phosphorescence regulated by graphitization and carbonyls

Abstract

Room-temperature phosphorescence with multiple-color activated the widespread interest owing to their promising applications, howbeit, there still exist the insurmountable challenge, especially for elucidating their photoluminescence mechanism and tunable emissions. Here we systematically proposed several carbon dots (CDs) with different degrees of graphitization and amounts of carbonyl while sulfuric acid and ethanol played the critical roles. In brief, sulfuric acid functioned as the carbonization and strong oxidization reagent, while the increasing volumes of ethanol gradually reduced the boiling point of the reactions. Significantly, the energy of these phosphorescent CDs transferred from their excited triplets to oxygen molecules once they were irradiated by UV in aqueous, resulting in the production of the singlet oxygen to oxidize 3,3′,5,5′-tetramethylbenzidine. This finding indirectly provided the evidence for the existence of the phosphorescence rather than delayed fluorescence. Towards the photoluminescence mechanism, their fluorescence of CDs was originated from π-π* transition of CC in the carbon cores and n-π* transition of CO on the surfaces, while RTP was mainly attributed to n-π* transition of the carbonyls. The further evidence suggested that the CDs with different graphitization degrees and amounts of CO regulated their multiple-color phosphorescence. Besides, we employed these CDs for information encryption and preparing LED lamps.