Efficient color-tunable room temperature phosphorescence through carbon dot confinement in urea crystals

Color-tunable phosphorescence has received extensive attention in recent years. Herein, a facile approach for the synthesis of carbon dots (CDs) in urea crystals (referred to as uCDs) is reported. Excitation dependence under ambient conditions and multicolor room temperature phosphorescence (RTP), changing from yellow–green (570 nm) to orange (610 nm) at excitation wavelengths of 365 and 460 nm, is observed in the synthesized uCDs. The multicolor emission can be attributed to the existence of multiple emitting centers in the uCDs and it is determined that hydrogen bonding plays a critical role in achieving RTP. High intensity phosphorescence was achieved by external heating of the prepared uCDs@150, which forms a tighter rigid urea matrix and results in an attained lifetime of 281 ms. Based on these unique color-tunable properties, the synthesized uCDs@150 have potential applications in anticounterfeiting and light-emitting diode technologies. This study not only proposes a strategy to prepare photo-stimulated multicolor RTP materials, but also reveals the potential of CDs in exploiting novel optical materials with unique properties. • Carbon dots with emission wavelength above 600 nm were successfully prepared. • Multiple emission centers exist for carbon dots. • By reheating, the luminescence intensity of carbon dots was increased by about 2 times. • The carbon dot afterglow lifetime was increased by about three times by reheating.