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摘要: 磷光碳点(CDs)因其具有长寿命、长波长发射、低背景干扰等优点,在能源、信息和生物医学等领域具有较大的潜力。但是,磷光CDs的制备及其发光机理依然面临一些挑战,如:其三重态极易受到外界环境的影响,从而导致磷光猝灭。因此,针对存在的问题,本文首先分析和总结了磷光CDs的起源以及杂元素掺杂、刚性结构和共轭结构等对磷光CDs结构和性能的影响;其次,从一步和两步法两方面综述了其合成方法;再次,归纳了磷光CDs在信息防伪、发光二极管、离子检测和生物成像等方面的应用研究;最后,提出目前仍然存在的问题,并展望了其研究和应用发展方向。Abstract: Phosphorescent carbon dots (CDs) have great potential in energy, information, biomedicine, and other fields because of their long lifetime, long wavelength emission, and low background interference. However, there are still some challenges in their preparation and understanding their luminescence mechanism. For example, their triplet states are easily affected by the external environment, which leads to phosphorescence quenching. The phosphorescence mechanism and the effects of element doping, rigidity of structure, and conjugated structure on their properties are reviewed to address these issues. The synthesis methods include one step and two step methods. The uses of phosphorescent CDs are summarized and include information security, light emitting diodes, ion detection, and biological imaging. The existing problems are discussed and development directions are proposed.
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Key words:
- Carbon dots /
- Phosphorescence /
- Structure /
- Synthesis /
- Application
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Figure 3. (a) Digital photographs of RTP CDs, (b) phosphorescence excitation spectrum (olive dots) and absorption spectrum of RTP CDs dispersed in water (blue dots)[42], (c) high resolution XPS spectra of RTP CDs, (d) representation of the tunable phosphorescence emission from RTP CDs[44], (e) FTIR spectrum of RTP CDs, (f) high-resolution N1s XPS spectrum of RTP CDs and (g) the UV-Vis diffuse reflectance (red line), PL excitation (PLE) and emission (PL) spectra of RTP CD powder (inset: RTP CDs powder under daylight and UV lamp (365 nm) irradiation)[32]. Reprinted with permission.
Figure 4. High resolution XPS spectra of O1s and P2p for RTP CDs[49]. Reprinted with permission.
Figure 5. RTP emission spectra of URTP-CDs, EG-CDs and S-CDs powders under excitation of 340 nm[37]. Reprinted with permission.
Figure 6. (a) TEM images , (b) HRTEM images of RTP CDs[59], (c) schematic illustration of the possible structural formation of CDs@SiO2[60], (d) schematic of the design strategy of the multi-confined (rigid network, stable covalent bonds, and three-dimensional nano-space) phosphorescence[61], (e) TEM image of CDs@MP dispersion, (f) CDs@MP without matrices[51]and (g) N-doped CDs are embedded into recrystallized molten urea and biuret matrices[47]. Reprinted with permission.
Figure 7. (a) Phosphorescence mechanism of N-doped CDs[43], (b) schematic illustration for RTP mechanisms of CDs[64], (c) phosphorescence mechanism of RTP CDs, (d) schematic structure of crosslinking sites, (e) energy level diagrams of single luminescence unit and (f) coupled luminescence units[36]. Reprinted with permission.
Figure 8. (a) Schematic illustration of polymer/carbon hybrid structure variation in RTP CDs with increasing the carbonization degree[48], (b) normalized PL of RTP CD powders measured under 360 nm excitation, (c) schematic representation of four different CDs[66], (d) schematic illustration for the synthetic procedure of CDs[64], (e) schematic of the procedure used for the preparation of N-doped CDs[32] and (f) synthesis of N-doped CDs[43]. Reprinted with permission.
Figure 9. Schematic of the overall process for fabrication of CDs@SiO2 RTP materials with a ultralong lifetime from rice husks (RHs)[69]. Reprinted with permission.
Figure 11. (a−c) Photographs of the inks in quartz cells under daylight and under UV light at 365 nm (Photographs of the printed patterns on papers under excitation at 254, 365 and 450 nm (ON) and after closing the excitation (OFF))[33], (d, e) photographs of the RTP CD-based inks and potential applications[38] and (f) schematic illustration of the time division duplexing based on the RTP CDs and RTP CDs@silica[70]. Reprinted with permission.
Figure 12. (a) Emission color coordinates of assembled LEDs[47], (b) emission spectra of the CD-based six WLEDs, (c) photographs of six WLEDs with adjustable CCTs, (d) CIE chromaticity diagram showing the color coordinates of the six WLEDs[66], (e) phosphorescence emission spectra of CDs@LDHs under different oxygen concentrations, (f) plots of I0/I1 as a function of the oxygen concentration[44], (g) phosphorescence spectra of RTP CDs at various calculated concentrations of Fe3+and (h) phosphorescence emission intensity ratio depends on the concentration of the added Fe3+[72]. Reprinted with permission.
Figure 13. Photographs of fingerprints on different substrates[69]. Reprinted with permission.
Table 1. A summary of the preparation methods and properties of RTP-CDs.
Application Precursor Method RTP CDs Life times (ms) PQY RTP Em (nm) Refs. Anti-counterfeiting and information encryption 2-Methyl-2,4-pentanediol One-step hydrothermal
(180 ℃, 12 h)N-doped CDs@PVA 2260 8.7% 530 [59] Folic acid, Urea One-step hydrothermal
(260 ℃, 2 h)N-doped CDs@urea 530 500 [33] Folic acid, Urea One-step hydrothermal
(260 ℃, 2 h)700 500 o-Phenylenediamine, Urea One-step hydrothermal
(180 ℃, 2 h)120 625 Ethylenediamine Heating (180 ℃, 2 h) N, P-doped CDs 1390 538 [38] Ethylenediamine, Phosphoric acid Microwave (750 W, 130 s) N, P-doped CDs 1270 12.6% 520 [70] WLED Urea Heating (195 ℃, 10 h) N-doped CDs 235 520 [71] Folic acid One-step hydrothermal
(260 ℃, 2 h)N-doped CDs 930 490 [47] Urea, seed CDs Hydrothermal reaction
(180 ℃, 4 h)N-doped CDs@PVP 419 596 [66] Detection Ethylene diamine tetraacetic acid Calcination method
(300 ℃, 4 h)CDs@LDHs 386.8 525 [44] Anhydrous citric acid, Folic acid Hydrothermal reaction
(240 ℃, 4 h)N-doped CDs@silica 705 14% 470 [72] Triethanolamine Microwave (65 W, 3 min) N, P-doped CDs 15.85% 518 [68] Rice husk, Ethylenediamine Magnetic stirring
(180 ℃, 6 h)CDs@SiO2 1620 507 [69] Biological imaging application Ethylenediamine, Phosphoric acid Microwave (750 W, 130 s) N-doped CDs 1860 11.6% 505 [73] -
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