Research progress of carbon dots based white light emitting fluorescent films
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摘要: 碳点 (Carbon dots,CDs) 具有制备简单、来源广泛、毒性低和光学性能优异等特性,可作为发光材料应用于固态照明器件中。基于CDs荧光薄膜的制备及实现其白光发射的方式不同,使其白光荧光薄膜的性能各异。首先,介绍了CDs的光致发光机制;其次,根据CDs荧光薄膜的形成方式归纳为CDs/聚合物荧光薄膜和CDs自组装荧光薄膜两类,并介绍其制备方法;然后,根据荧光薄膜中所含荧光材料的种类,将实现荧光薄膜白光发射的方式概括为两种:混合多色荧光材料和使用单一白光CDs;最后,提出白光CDs及其荧光薄膜目前存在的问题,并展望其进一步的发展。Abstract: Carbon dots (CDs) have many excellent characteristics, including simple preparation, abundant sources, low toxicity and excellent optical properties, that can be served as fluorescent materials to prepare fluorescent films for solid-state lighting devices. The different ways of the CDs-based film formation and their white light emission make the variety properties of fluorescent films. Firstly, the photoluminescence mechanisms of CDs are introduced. Secondly, the fluorescent films are divided into two categories based on the film formations: CDs/polymer fluorescent films and CDs self-assembled fluorescent films, and their preparation methods are summarized. Thirdly, according to the types of fluorescent materials in the fluorescent film, two means of realizing white light emission of fluorescent films are introduced by mixing polychromatic fluorescent materials and using single white light CDs. Finally, the problems of CDs and their fluorescent films and the prospects for development of CDs-based fluorescent films are discussed.
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Key words:
- carbon dots /
- polymer matrix composites /
- fluorescent films /
- white light emission /
- methods
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图 2 (a) 溶剂热法制备蓝-红CQDs的示意图;(b) 最高占据分子轨道(HOMO)和最低未占据分子轨道(LUMO)能级与CQDs大小的依赖关系[24];(c) 在添加和不添加酒石酸 (TA) 的情况下,使用间苯二胺和邻苯二胺制备多色CDs的工艺示意图;所获得的b-CDs、g-CDs、y-CDs和r-CDs在自然光(d)和365 nm紫外光(e)下在乙醇中分散的照片;(f) 在365 nm激发下,多色CDs (在乙醇中) 归一化的PL谱图[25];(g) CDs 合成的原理图[27]
Figure 2. (a) Preparation of CQDs from blue to red by solvothermal treatment; (b) Dependence of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels with respect to the size of CQDs [24]; (c) Schematic illustration of the preparation process for multicolor CDs using m- and o-phenylenediamines in the absence and presence of tartaric acid (TA), respectively; Photographs of the obtained b-CDs, g-CDs, y-CDs, and r-CDs dispersions in ethanol under natural light (d) and 365 nm UV light (e), respectively; (f) Normalized PL emission spectra of the multicolor CDs (in ethanol) under excitation of 365 nm [25]; (g) Schematic diagram of synthesizing CDs [27]
图 3 (a) 不同pH值下,520 nm波长激发的红光CDs的PL光谱[35];(b) CDs在不同不混溶溶剂中的双色荧光层[36];(c) 随压力的增加而变化的CDs的PL光谱[41]
Figure 3. (a) PL spectra of the red-emitting CDs at different pH values under excitation at 520 nm [35]; (b) Two-color fluorescent layers of CDs in different immiscible solvents [36]; (c) PL spectra change of CDs as the pressure increases [41]
图 4 CDs/环氧树脂荧光薄膜的透射光谱图(a)和CDs质量分数与薄膜厚度的关系(b)[43];CDs/聚乙烯醇 (PVA) 荧光薄膜的结构(c)及其水响应形状记忆功能(d)原理图;纯PVA和CDs/PVA荧光薄膜在自然光(e)和 紫外光(f)下的照片及CDs/PVA荧光薄膜在室温下并在自然光(g)和紫外光(h)下的形状恢复过程[51]
Figure 4. Transmission spectra and relationship between the mass fraction of CDs (a) and the thickness of CDs/epoxy fluorescent film (b) [43]; Structure (c) and water-responsive shape memory mechanism (d) of CDs/Poly (vinyl alcohol) (PVA) fluorescent film; Photograph of pure PVA and CDs/PVA fluorescent film under natural (e) and UV light (f), and shape recovery process of CDs/PVA fluorescent film at room temperature under natural (e) and UV light (f)[51]
图 5 (a) 绿光CDs (G-CDs) /甲基三乙氧基硅烷 (MTES) 和红光CDs (R-CDs) /3-氨基丙基-三乙氧基硅烷 (APTES) 的制备及其在LED中的应用[52];(b) CDs/PEI荧光薄膜的形成机制[54];
Figure 5. (a) Preparations of green light CDs (G-CDs) /Methyltriethoxysilane (MTES) and red light CDs (R-CDs) /3-amino-propyl-triethoxysilane (APTES) and their applications in LED [52]; (b) Formation mechanism of CDs/PEI fluorescent film [54]
图 6 (a) CDs/聚丙烯酰胺/聚丙烯酸 (CDs/AA/AAc) 凝胶薄膜的制备流程图[58];(b) 多色LED的发光光谱;(c) 白光LED的色坐标 (插图为工作状态下的发光图);(d) 白光LED的发光光谱; (e) 在开始和工作20天后的发光谱图[64];(f) 白光 CDs (W-CDs) 的制备工艺图,插图为其在自然光 (左) 和紫外光 (右) 下的照片[70]
Figure 6. (a) Schematic diagram for preparation process of CDs/Acrylamide/Acrylic Acid (CDs/AA/AAc) hydrogel film [58]; Characterization of LEDs fabricated using the CDs: (b) Emitting light spectrum of multicolor LEDs; (c) CIE color coordinates of the white LEDs (Inset at right top corner is the optical photograph of the white LED at on-state); (d) Emitting light spectrum of white LEDs; (e) Emitting spectra of the white LED at initial and after illustrating over 20 days [64]; (f) Schematic illustration of the formation process and structure of the W-CDs, inset: Photographs of the W-CDs under natural light (left) and UV lamp (right) (365 nm) [70]
表 1 白光CDs及其荧光薄膜在LED中的应用[31, 69-80]
Table 1. Applications of white light CDs and their fluorescent films in LEDs [31, 69-80]
λex/nm
(for CDs)PL range/nm QY/% State Film λex/nm
(for UV chip)CCT/K CRI CIE Ref 400 400-750 29 Liquid CDs/HEMA 400 — 92 (0.33, 0.33) [31] 350 400-800 11 Liquid CDs/PVA 365 7023 — (0.30, 0.33) [69] 365 400-700 6.7 Solid CDs/epoxy 365 6987 83 (0.30, 0.35) [70] 365 400-600 9.6 Liquid CDs/PMMA 365 — — (0.24, 0.33) [71] 365 400-750 10 Solid — 400 3032 91 (0.42, 0.38) [72] 380 400-800 12.7 Liquid CDs/PVP 380 5136 80 (0.33, 0.33) [73] 340 380-700 17.81 Liquid CDs/PVA 340 8442 74 (0.29, 0.33) [74] 365 550-800 29.7 Liquid CDs/PVP 365 5475 88 (0.35, 0.36) [75] 365 380-800 39 Liquid CDs/PMMA 365 5994 86.7 (0.33, 0.33) [76] 365 400-750 41 Solid — 380 4935 85 (0.35, 0.39) [77] 375 400-700 41 Solid — 370 8756 85.3 (0.27, 0.35) [78] 365 400-650 — Liquid CDs/PVB 365 — — (0.32, 0.31) [79] 365 400-750 46 Solid CDs/Silicone resin 365 5028 82 (0.34, 0.38) [80] Notes: λex—Excitation wavelength; QY—Quantum yield; CCT—Correlated color temperature; CRI—Color rendering index; CIE—Commission Internationale de l'Eclairage; HEMA—2-Hydroxyethyl methacrylate; PMMA—Poly(methyl methacrylate); PVP—Polyvinylpyrrolidone; PVB—Polyvinyl Butyral. -
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