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Conversion of Carbon Dots from Fluorescence to Ultralong Room‐Temperature Phosphorescence by Heating for Security Applications
Author(s) -
Jiang Kai,
Wang Yuhui,
Cai Congzhong,
Lin Hengwei
Publication year - 2018
Publication title -
advanced materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.707
H-Index - 527
eISSN - 1521-4095
pISSN - 0935-9648
DOI - 10.1002/adma.201800783
Subject(s) - phosphorescence , materials science , intersystem crossing , fluorescence , nanotechnology , quantum dot , photochemistry , aqueous solution , excited state , organic chemistry , chemistry , optics , physics , nuclear physics , singlet state
Stimuli‐responsive optical materials have received tremendous interest in the last several decades due to their numerous promising applications. Here, fluorescence emissive polymer carbon dots (F‐CDs), prepared with a simple heating treatment from ethylenediamine and phosphoric acid, are found to produce unexpected ultralong room‐temperature phosphorescence (URTP), which lasts for about 10 s with a lifetime of 1.39 s. This is the first example to achieve the conversion of a fluorescence material to URTP by means of an external heating stimulus. Further investigations reveal that the doping of N and P elements and self‐immobilization of the excited triplet species are likely mainly responsible for the observed URTP after the heating treatment, due to the facilitation of the intersystem crossing and formation of more compact cores for effective intraparticle hydrogen bonds, respectively. Importantly, this study also demonstrates the potential for aqueous dispersion of the F‐CDs as an advanced security ink for information encryption and anticounterfeiting; this is a feature that has not been reported before. This study is believed to open possibilities to extend stimuli‐responsive optical materials to rarely exploited phosphorescence‐relevant systems and applications, and also to provide a novel strategy to easily prepare URTP materials.