Temperature-controlled spectral tuning of full-color carbon dots and their strongly fluorescent solid-state polymer composites for light-emitting diodes

The development of full-color/white carbon-dot-based light-emitting diodes (LEDs) has been achieved, which show promising applications in full-color and flexible displays, backlights, and novel lighting sources. The gram-level synthesis of these full-color carbon dots (CDs) from citric acid by controlling the temperature has been achieved. By increasing the temperature from 120 to 180 °C, two, four, and six light-emitting CDs can be obtained, for which the emission wavelength shifts from 440 to 585 nm. This result reveals that temperature has a huge impact on the evolution of surface states, that is, increasing the temperature brings about enhanced surface functionalization and passivation, resulting in a red shift of the emission wavelength and enhancement of quantum yield. Then, full-color CDs/polymer composite phosphors are fabricated for efficient phosphor-based LED devices with quench-resistant solid-state fluorescence. By regulating the proportion of various CDs/polymer phosphors, white LEDs are realized with Commission Internationale de L'Eclairage coordinates of (0.32, 0.33) and a color rendering index of 82.7. The as-prepared CD-based full/white color LEDs can prove to be promising candidates for alternative light sources.


Figure S5 .
Figure S5.The absorption curves, excitation and emission spectra of B-CDs (A), G-CDs (B), Y-CDs (C) and O-CDs (D), prepared at 180℃, respectively.Inset legends are photographs of the four samples in aqueous solution under daylight (left) and UV light (right).

Figure S9 .
Figure S9.At% ratio of N/O in B-CDs, G-CDs, Y-CDs and O-CDs, prepared at 180℃, respectively.

Figure S16 .
Figure S16.A: the pictures of B-CDs, G-CDs, Y-CDs and O-CDs under 365nm UV light, respectively; B: the images of B-CDs/PVP, G-CDs/PVP, Y-CDs/PVP and O-CDs/PVP under 365nm UV light, respectively; C: the photoes of four LEDs under fixed voltage, with CDs/PVP powder as emitting layers, respectively.

Figure S17 .
Figure S17.Schematic diagram of the anti-aggregation-induced quenching effect.

Figure S24 .
Figure S24.Relative PL intensity of multi-color emissive CDs and CDs/PVA films kept for up to 10h at 365 nm UV light irradiation.A: B-, G-, Y-, and O-CDs; B: B-, G-, Y-, and O-CDs/PVA films.

Figure S25 .
Figure S25.Relative PL intensity of multi-color emissive CDs and CDs/PVA films kept for 1 h under different temperatures as indicated.A: B-, G-, Y-, and O-CDs; B: B-, G-, Y-, and O-CDs/PVA films.

Figure S26 .
Figure S26.The photoes of four LEDs under different voltage, with CDs/PVA films as emitting layers.

Table S1 .
Band-gap energy data Analyses of four typical CDs, prepared at 180℃.

Table S2 .
Fluorescent lifetime and relative quantum yield data analyses of the four special CDs, prepared at 180℃, respectively.

Table S3 .
Fluorescent lifetime and relative quantum yield data analyses of the four CDs/PVA films.