Graphitic carbon nitride quantum dots embedded in magnesium fluoride: Achieving blue-violet room-temperature phosphorescence for information encryption and fingerprint detection
Hailiang Yang, Mingyu Xin, Longyue Zhang, D. Guo, Qian Chen, Yuankui Huang, Xipao Chen, Yaoping Hu
Abstract
Graphitic carbon nitride quantum dots (g-CNQDs) with exceptional fluorescence properties have potential applications in various fields, but their phosphorescence characteristics and associated mechanisms have received considerably less attention. This study presents the room-temperature phosphorescence (RTP) from g-CNQDs by embedding them into a magnesium fluoride (MgF 2 ) matrix. The g-CNQDs were synthesized by hydrothermal treatment of graphitic carbon nitride in an aqueous H 2 O 2 solution. Calcining the mixture of g-CNQDs, magnesium nitrate, and ammonium fluoride at 300–700°C resulted in the production of g-CNQDs@MgF 2 composites. Systematic investigations reveal that the phosphorescence originates from the triplet excited states of the π-conjugated structures of tri-s-triazine rings in the core of g-CNQDs. The MgF 2 matrix provides multiple constraints on g-CNQDs through a rigid network and robust covalent and hydrogen bonds, which effectively stabilize the triplet excitons and suppress the non-radiative transitions, enabling long-lasting blue-violet RTP with an optimal lifetime of 214 ms. By adjusting the calcination temperature, the phosphorescence properties of g-CNQDs@MgF 2 can be finely tuned. The composites possess outstanding optical stability against different solvents, strong acids, and bases, and show promising applications in information encryption and fingerprint detection, offering a cost-effective and environmentally friendly alternative to conventional RTP materials.