Matrix-Free and Highly Efficient Room-Temperature Phosphorescence of Nitrogen-Doped Carbon Dots

Efficient room-temperature phosphorescence (RTP) of carbon dots (CDs) usually is seriously limited to appropriate solid matrix or introduced heavy atoms responsible for promoting intersystem crossing and suppress vibrational dissipation between singlet and triplet states. So, facile preparation efficient RTP of CDs with nonmatrix is still a highly difficulty and challenging task. Here, we first reported a subtle strategy to induce highly efficient free-matrix RTP of nitrogen-doped CDs (NCDs). The NCDs are composed of a core and hydrophilic surface of polyaspartic acid chains arising from high-temperature polymerization by a one-pot heating treatment of l-aspartic acid and d-glucose. The obtained NCDs have an ultralong phosphorescence lifetime of 747 ms and a high phosphorescence quantum yield (PQY) of 35% under 320 nm excitation in air. To the best of our knowledge, the PQY is currently the highest values recorded for RTP of CDs. The facile preparation and unique optical features offer these NCDs potential application in numerous applications, such as anticounterfeiting and white light-emitting diodes.