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. 2020 Oct 2;6(40):eabb6772.
doi: 10.1126/sciadv.abb6772. Print 2020 Oct.

Full-color fluorescent carbon quantum dots

Liang Wang  1   2 , Weitao Li  3 , Luqiao Yin  4 , Yijian Liu  3 , Huazhang Guo  3 , Jiawei Lai  2 , Yu Han  3 , Gao Li  3 , Ming Li  3 , Jianhua Zhang  4 , Robert Vajtai  2 , Pulickel M Ajayan  2 , Minghong Wu  1
Affiliations

Full-color fluorescent carbon quantum dots

Liang Wang et al. Sci Adv. .

Abstract

Quantum dots have innate advantages as the key component of optoelectronic devices. For white light-emitting diodes (WLEDs), the modulation of the spectrum and color of the device often involves various quantum dots of different emission wavelengths. Here, we fabricate a series of carbon quantum dots (CQDs) through a scalable acid reagent engineering strategy. The growing electron-withdrawing groups on the surface of CQDs that originated from acid reagents boost their photoluminescence wavelength red shift and raise their particle sizes, elucidating the quantum size effect. These CQDs emit bright and remarkably stable full-color fluorescence ranging from blue to red light and even white light. Full-color emissive polymer films and all types of high-color rendering index WLEDs are synthesized by mixing multiple kinds of CQDs in appropriate ratios. The universal electron-donating/withdrawing group engineering approach for synthesizing tunable emissive CQDs will facilitate the progress of carbon-based luminescent materials for manufacturing forward-looking films and devices.

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Figures

Fig. 1
Fig. 1. Synthetic strategy of full-color fluorescent CQDs.
(A) An acid reagent engineering strategy for the synthesis of full-color fluorescent CQDs using oPD as the precursor. (B) Fluorescence photographs of CQDs under UV light (excited at 365 nm).
Fig. 2
Fig. 2. Morphological characterizations of selected CQDs.
(A to E) TEM images and corresponding lateral size distributions of b-CQDs (A), c-CQDs (B), yg-CQDs (C), o-CQDs (D), and r-CQDs (E). (F to J) High-resolution TEM images of b-CQDs (F), c-CQDs (G), yg-CQDs (H), o-CQDs (I), and r-CQDs (J) (inset: fast Fourier transform patterns). (K to O) AFM images and corresponding height profiles of b-CQDs (K), c-CQDs (L), yg-CQDs (M), o-CQDs (N), and r-CQDs (O).
Fig. 3
Fig. 3. Optical performance of selected CQDs.
(A) Absorption spectra of CQDs. (B) Normalized PL spectra of CQDs. (C) Dependence of the PL wavelength and first excitonic absorption band on the particle size of CQDs. (D) Time-resolved PL spectra of CQDs. (E) Dependence of the HOMO and LUMO energy levels concerning the particle size of CQDs. a.u., arbitrary units.
Fig. 4
Fig. 4. Optical and morphological characterizations of w-CQDs.
(A) Photographs of w-CQDs under daylight (left) and UV light (right) (excited at 365 nm). (B) PL spectrum of w-CQDs. (C) Time-resolved PL spectrum of w-CQDs. (D) TEM image and corresponding lateral size distribution of w-CQDs. (E) High-resolution TEM image and fast Fourier transform pattern of w-CQDs. (F) AFM image and corresponding height profile of w-CQDs.
Fig. 5
Fig. 5. Applications of full-color CQDs.
(A) Fluorescence images of CQDs/PMMA composite films on glass substrates under UV light. (i) b-CQDs, (ii) c-CQDs, (iii) g-CQDs, (iv) y-CQDs/g-CQDs = 1:1, (v) yg-CQDs, (vi) y-CQDs, (vii) g-CQDs/o-CQDs = 1:1, (viii) o-CQDs, (ix) yg-CQDs/o-CQDs = 1:1, (x) r-CQDs/dr-CQDs = 1:1, (xi) dr-CQDs/b-CQDs = 1:1, (xii) r-CQDs, (xiii) dr-CQDs, (xiv) b-CQDs/yg-CQDs/dr-CQDs = 1:2:3, (xv) c-CQDs/y-CQDs/r-CQDs = 1:2:1, and (xvi) w-CQDs (all ratio scale w/w). (B and E) The CIE chromaticity coordinate and corresponding emission spectrum of the warm WLED (inset: the photograph and schematic of the warm WLED). (C and F) The CIE chromaticity coordinate and corresponding emission spectrum of the standard WLED (inset: the photograph and schematic of the standard WLED). (D and G) The CIE chromaticity coordinate and corresponding emission spectrum of the cool WLED (inset: the photograph and schematic of the cool WLED).
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