Mechanism of in situ confining carbon dots in phthalamide crystal for room-temperature phosphorescence†

Abstract

Carbon dot (CD)-based room temperature phosphorescence (RTP) materials have widespread applications in anti-counterfeiting, light-emitting diode (LED) lighting, and bioimaging due to their spectral tunability, long lifetime, and other excellent optical properties. However, challenges remain regarding their complicated preparation processes and unclear mechanism. In this work, we developed a one-step, in situ liquid-phase synthesis method using phthalic acid, formamide, and ethylene glycol to directly form RTP CDs@phthalamide composites with CD/organic crystal structures. The product required only filtration and drying without further post-processing, significantly simplifying the preparation procedure and facilitating large-scale production. The as-prepared CDs@phthalamide exhibit excitation-dependent phosphorescence with a naked-eye-visible afterglow of 5 s and a phosphorescence lifetime of 441 ms. The formation process and reaction mechanism of CDs@phthalamide were investigated by optimizing the reaction temperature and reaction time, calculating activation energies through theoretical simulations, and comparing the effect of different crystal structures of phthalamide and phthalimide crystals on luminescence. Unlike phthalimide, the phthalamide matrix effectively restricts the vibration and rotation of CD luminous centers, realizing efficient RTP emission. Density functional theory (DFT) calculations further verified that the N elements enhanced RTP performance. In addition, CDs@phthalamide shows potential application value in time-delayed LEDs and anti-counterfeiting.