Kai Jiang1,2, Yuhui Wang1, Congzhong Cai2, Hengwei Lin1. 1. Key Laboratory of Graphene Technologies and Applications of Zhejiang Province, Ningbo Institute of Materials Technology & Engineering (NIMTE), Chinese Academy of Sciences, Ningbo, 315201, China. 2. State Key Laboratory of Coal Mine Disaster Dynamics and Control, Department of Applied Physics, Chongqing University, Chongqing, 400044, China.
Abstract
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.
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 simpn>le heating treatment from n>an class="Chemical">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.