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

Abstract

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.

Rapid Preparation of Long-Wavelength Emissive Carbon Dots for Information Encryption Using the Microwave-Assisted Method

“…The analysis of the C 1s high-resolution XPS energy spectrum (Figure a) of (Y, O, R)-CDs shows that the four binding energy peaks at 282.3, 284.7, 285.8, and 286.9 eV of Y-CDs and O-CDs correspond to C–C, CC, C–N/C–O, and CO bonds, respectively, and the binding energy peaks of these bonds appear at 284.5, 285.3, 287.5, and 288.7 eV in R-CDs. − In addition, R-CDs also exhibit C–B bond peaks at 283.6 eV . The XPS spectra of N 1s in (Y, O, R)-CDs (Figure b) show that N elements mainly exist in the form of B–N (398.7 eV), pyridinic N (399.6 eV), amino N (400.2 eV), and graphitic N (400.8 eV). , The O element in (Y, O, R)-CDs mainly exists in the form of CO (531.0 eV), C–O–C (532.2 eV), and C–O (532.9 eV) (Figure c). , The XPS spectrum of B 1s (Figure d) shows that at 190.3 and 191.2 eV, it corresponds to the B–N and B–O bonds of (Y, O, R)-CDs, while at 189.6 eV, it belongs to the B–C bond of R-CDs. , The proportion of each chemical bond in (Y, O, R)-CDs is obtained by calculating the integral area (Table ). From Y-CDs to R-CDs, the content of C–N/C–O increased from 10.61 to 22.35% and B–C increased from 0 to 15.74%.…”

“…34 The XPS spectra of N 1s in (Y, O, R)-CDs (Figure 2b) show that N elements mainly exist in the form of B−N (398.7 eV), pyridinic N (399.6 eV), amino N (400.2 eV), and graphitic N (400.8 eV). 35,36 The O element in (Y, O, R)-CDs mainly exists in the form of C�O (531.0 eV), C−O−C (532.2 eV), and C−O (532.9 eV) (Figure 2c). 37,38 The XPS spectrum of B 1s (Figure 2d) shows that at 190.3 and 191.2 eV, it corresponds to the B−N and B−O bonds of (Y, O, R)-CDs, while at 189.6 eV, it belongs to the B−C bond of R-CDs.…”

Pyrene as a Triplet Acceptor Enhancing Triplet Energy Transfer of g-C3N4 in Heterogeneous Photooxidation

“…The heterogeneous bulk photosensitizers easily trap triplet excitons and inhibit photocatalysis efficiency. Previous work focused on controlling ultra-small size to reduce the transfer distance, , modifying the structure, and doping heteroatoms to promote ISC efficiency. However, these strategies suffer from issues of complex preparation methods and poor stability.…”

Large-Scale Syntheses of Multicolor Stimulus Responsive Room-Temperature Phosphorescent Polymer-Carbonyl-Modified Carbon Nitrogen Quantum Dots

“…9,10 Upon introduction of heteroatoms or heavy atoms, CNQDs can exhibit the RTP property because of the enhancement of intersystem crossing (ISC). 11,12 Recently, solid-state carbonyl-modified carbon nitrogen quantum dots (m-O�CNQDs) using urea as precursors have been achieved with a solid-phase heating method, which are promising phosphorescent materials close to commercialization owing to the strong ISC caused by carbonyl groups, low-cost precursors, and simple preparation method. 13 However, the exploitation of m-O�CNQDs in stimulus responsive fields is still limited by their insensitivity to external stimuli such as water and heat due to strong stacking interactions between layers arising from their high crystallinity.…”

“…Thus, it is meaningful and necessary to develop new low-cost, nontoxic, and stimulus responsive RTP materials with a simple preparation method. At present, carbon nitride quantum dots (CNQDs) have attracted a great deal of attention due to their unique and tunable optical properties, along with their low price, simple preparation method, and environmentally friendly nature. , Upon introduction of heteroatoms or heavy atoms, CNQDs can exhibit the RTP property because of the enhancement of intersystem crossing (ISC). , Recently, solid-state carbonyl-modified carbon nitrogen quantum dots ( m -OCNQDs) using urea as precursors have been achieved with a solid-phase heating method, which are promising phosphorescent materials close to commercialization owing to the strong ISC caused by carbonyl groups, low-cost precursors, and simple preparation method . However, the exploitation of m -OCNQDs in stimulus responsive fields is still limited by their insensitivity to external stimuli such as water and heat due to strong stacking interactions between layers arising from their high crystallinity. , Therefore, inhibiting stacking and increasing the affinity of m -OCNQDs for water are pressing needs for improving water stimulus responsive performance.…”