Rational Design of Multi-Color-Emissive Carbon Dots in a Single Reaction System by Hydrothermal.

Boyang Wang,Jingkun Yu,Siyu Lu,Shoujun Zhu,Laizhi Sui,Bai Yang,Zhiyong Tang

doi:10.1002/advs.202001453

Abstract

As an emerging building unit, carbon dots (CDs) have been igniting the revolutionaries in the fields of optoelectronics, biomedicine, and bioimaging. However, the difficulty of synthesizing CDs in aqueous solution with full‐spectrum emission severely hinders further investigation of their emission mechanism and their extensive applications in white light emitting diodes (LEDs). Here, the full‐color‐emission CDs with a unique structure consisting of sp 3‐hybridized carbon cores with small domains of partially sp 2‐hybridized carbon atoms are reported. First‐principle calculations are initially used to predict that the transformation from sp 3 to sp 2 hybridization redshifts the emission of CDs. Guided by the theoretical predictions, a simple, convenient, and controllable route to hydrothermally prepare CDs in a single reaction system is developed. The prepared CDs have full‐spectrum emission with an unprecedented two‐photon emission across the whole visible color range. These full‐color‐emission CDs can be further nurtured by slight modifications of the reaction conditions (e.g., temperature, pH) to generate the emission color from blue to red. Finally a flexible LEDs with full‐color emission by using epoxy CDs films is developed, indicating that the strategy affords an industry translational potential over traditional fluorophores.

Highlights

As an emerging building unit, carbon dots (CDs) have been igniting the in multi-color display, low-cost backlighting in liquid-crystal displays, and revolutionaries in the fields of optoelectronics, biomedicine, and bioimaging
Our proposed CDs are considered as sp3-hybridized carbon cores with small domains of sp2-hybridized carbon and systematically investigated by density functional theory (DFT) calculations
The smallest CDs emit at 417.12 nm, whereas the larger CDs emit at 626.87 nm (Table S1, Supporting Information), indicating that the emission wavelengths can cover the entire visible spectrum

Summary

Results and Discussion

We propose the optical responses of the multicolor-emissive CDs can be achieved by a simple, accurate, semianalytical model of the CDs optical centers.[22,23] Our proposed CDs are considered as sp3-hybridized carbon cores with small domains of sp2-hybridized carbon and systematically investigated by density functional theory (DFT) calculations. To illustrate the contributions of the different functional groups to the PL of CDs, their surface structures were controlled by using NaBH4, which is commonly used to reduce aldehydes and ketones to alcohols, and by using NaOH, which reacts with acidic groups on the CDs surfaces.[35] Adding NaBH4 and NaOH to the CDs affects the fluorescence intensity, but not the emission peak position, indicating that the surface state is inert (Figures S5 and S6, Supporting Information). The discs showed a range of colors because of the added CDs. All the discs were transparent and emitted various uniform colors from blue to red under the corresponding excitation light (Figure S8, Supporting Information). The resulting correlated color temperature and color rendering index (CRI) were 5452 K and 88, which suggests that our method is suitable for fabricating white LEDs with high CRI

Conclusion

Experimental Section

Conflict of Interest