Shallow Traps in Carbon Nitride Quantum Dots to Achieve 6.47 s Ultralong Lifetime and Wavelength-Tunable Room Temperature Phosphorescence

Room temperature phosphorescent (RTP) carbon dots (CDs) have the defects of short lifetime, single wavelength, and poor stability. Most approaches to achieve RTP CDs are based on stabilizing excited triplet state excitons and suppressing nonradiative transitions by providing a rigid environment. The internal structure of CDs has not been followed to address the issue of triplet state exciton quenching. Herein, boron (B) is doped into the framework of carbon nitride quantum dots (CNQDs) to create B-N bonds and generate trap state, thus reducing the degree of conjugation and constructing defects. The excited triplet excitons are captured by the defects and stored in the traps from which they escape under thermal activation-this in turn gives rise to an ultralong lifetime RTP. Based on the abovementioned considerations, 6.47 s ultralong-lifetime deep blue RTP CNQDs with phosphorescent emission wavelength at 418 nm are achieved. This is a significantly longer lifetime than for most deep-blue RTP CDs. By increasing the conjugation of the precursor, another 1.55 s of green RTP CNQDs at 530 nm is obtained. The difference in lifetime and wavelength between the two phosphorescent CNQDs as well as their excellent stability leads to potential applications in anti-counterfeiting and information encryption.