Recently,
the multicolor fluorescent carbon dots (CDs) have drawn
much attention due to their various applications. Herein, we report
multicolor emissive CDs by solvent-controlled and solvent-responded
approaches. The blue to red color emissive CDs are obtained by the
solvothermal method by varying the solvent during the reaction. The
red color emissive CDs (R-CDs) with good quantum yield is obtained
in a water medium. The detailed characterization revealed that the
solvent controls the particle size, band gap, and nitrogen doping
concentration. Specifically, in the protic solvent, the high N content
and presence of imine nitrogen are the reason for red emission. However,
in an aprotic solvent, the least N doping and a lack of C–O
groups are responsible for a blueshift. Interestingly, it was observed
that the R-CDs provide a full range of visible color by dispersing
in different immiscible solvents. The fluorescence emission in immiscible
solvents is redshifted by enhancing the polarity. Moreover, the developed
CDs detected the low water concentrations (≤0.2%, v/v) visually
and fluorometrically in various organic solvents. Simultaneously,
we have employed synthesized CDs in white-light-emitting diodes and
fluorescent ink.
In
recent years, the tunable fluorescence emissive carbon dots
(CDs) enrich the efficacy and importance via the incorporation of
two or more applications. Herein, we report a pyromellitic acid-based
pH-responsive multicolor emissive (orange and green) manganese doped
CDs. The mechanism behind the tunable fluorescence properties at high
pH is proposed based upon the detailed optical and physicochemical
study. The result showed that the blue shifts are highly associated
with the COO moieties on the surface. Afterward, we have expanded
the applications of the synthesized CDs in a white-light-emitting
diode (WLED), fingerprinting, fluorescent ink, and bioimaging.
Multicolor tuning is one of the most remarkable features of carbon dots (CDs), used as a color convertor in making white-light-emitting diodes (WLEDs). Herein, a solvent-controlled method has been employed to prepare the multicolor-emissive CDs from 1,2,4-triaminobenzene and melamine, where the green-, orange-, and red-color-emissive carbon dots (G-, O-, and R-CDs) have been synthesized in acetone, water, and dimethylformamide (DMF), respectively. It has noted that the reaction solvent has impacted the growth of the particle size, elemental concentration, surface functionalization, and ultimately fluorescence emission. To avoid aggregation quenching emission (AQE), fluorescent polymeric films have been shaped by mixing poly(methyl methacrylate) (PMMA) with R-and G-CDs, while O-CDs was made with poly(vinyl alcohol) (PVA). Interestingly, PVA exhibited red-shifted emission of O-CDs from 585 to 597 nm in O-CDs/ PVA, while PMMA accompanied a blue-shifting emission. The enriched nitrogen and oxygen elemental contents, especially the graphitic N of O-CDs/PVA, and hydrogen-bonding affinity of PVA cause the red-shifted emission of O-CDs/PVA. Fluorescent solid films have been used to develop monochromatic and white-color-emissive light-emitting diodes. Further, all of the synthesized CDs served as carbon precursors to develop room-temperature phosphorescence (RTP) by a molten salt method, where only R-and O-CDs achieved their RTP emissions with different intensities. The mechanism behind the RTP formation with particular CDs and their emission intensity dependency has been studied by the C�O moieties.
Exploration of many strategies has continuously contributed to producing aggregation-induced red-emissive carbon dots (CDs). In this work, we designed fluorine-embedded (F-embedded) CDs from 1,2,4-triaminobenzene, thiourea, and ammonium fluoride (NH 4 F) exhibiting polymer-induced emission (PIE). The PIE phenomenon of fluorescent CDs is obtained in poly(vinyl alcohol) (PVA), showing emissions at 611 and 617 nm in the dispersed and solid states, respectively. The CDs exhibited a red shift of 28 nm in the PVA solution because PVA hydroxyl groups formed a robust bridge-like H-bonding network between CDs. The fluorine embedded in CDs enhanced the H-bond affinity toward PVA. It showed that this H-bond restricted the coupling of CDs' surface states and inhibited the nonirradiation transfer. For the solid state, surface PVA chains eliminated the π−π interaction of the conjugated core and constructed a selfquenching resistance polymeric system around CDs. As a result, CDs showed an unexpected red shift of fluorescence emission in PVA. Furthermore, white light-emitting diodes (WLEDs) have a correlated color temperature (CCT) of 5232 K, and a high color rendering index of 95 has been fabricated by integrating the red-and green-emissive films over the UV LEDs. Interestingly, the as-synthesized CDs showed room temperature phosphorescence (RTP), which enabled us to employ the CDs in double-security protection. Simultaneously, CDs have been used in fingerprint detection.
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