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• Solid-state fluorescence from Zn-doped CQDs@bioplastics nanocomposite is reported. • Zn-doped CQDs were synthesized from Brassicca juncea flower extract. • UVC-tube down-conversion was demonstrated with bioplastic nanocomposite. • Zn-doped bioplastic nanocomposite emits more brightly than the unintentional one. • CIE chromatic coordinates of (0.39, 0.56 vs. 0.29, 0.55) were obtained. The enhancement of solid-state fluorescence from nanocomposite bioplastics containing intentionally Zn-doped carbon quantum dots (CQDs) has been reported. For the synthesis of CQDs from Brassica juncea flower extract, an economical, ecologically sustainable, and one-step hydrothermal method was used. The morphological, structural, and physicochemical properties were examined. The quasi-circular shaped CQDs, with an average diameter of 4.7 nm, were discovered to emit yellow-greenish fluorescence upon UV stimulation, to have exceptional photostability, and to be highly water soluble, with a quantum yield of up to 18%. Furthermore, a commercial UVC-tube wrapped with bioplastic nanocomposite emitted a greenish-yellow colour where intentionally Zn-doped CQDs@bioplastic nanocomposite emits more intensely than an unintentional one with CIE chromatic coordinates (0.39, 0.56 vs. 0.29, 0.55). [ABSTRACT FROM AUTHOR]

Carbon quantum dots (CQDs)-based composite as a luminescent down-conversion materials are gaining importance nowadays because of many favorable factors including stable fluorescence, ease of functionalization, tuning of emission in visible range etc. In this work, we report an economical, sustainable and green synthesis of CQDs derived from mustard (Brassica juncea) flower extract. The as-synthesized CQDs were unintentionally doped with nitrogen and calcium without the inclusion of any doping element precursors. However, phosphorus was intentionally doped to improve the luminescent characteristics of as-synthesized CQDs. The morphological, structural, and physicochemical properties of P-doped CQDs were examined. The quasi-circular or polygonal-shaped CQDs, with an average diameter of 3.4 nm, emerged to produce yellow-greenish fluorescence upon UV stimulation, demonstrate outstanding photostability, and had a quantum yield of up to 18.2%. Furthermore, the ecologically friendly and biodegradable bioplastic is attractive as a solid phase dispersion matrix of CQDs. Hence, this work revealed the effect of phosphorus doping on solid-state fluorescence in the down-conversion of LEDs and UV tubes by producing a composite constructed through inserting CQDs into the solid-state matrix of corn-starch-based bioplastic. [Display omitted] • Effect of intentional P-doped in N,Ca-doped CQDs@bioplastic composite is reported. • Intentional P-doped CQDs were synthesized from Brassica juncea flower extract. • Down-conversion of LEDs and UV tubes have been demonstrated. • Influence of pH on fluorescence properties have also been investigated. [ABSTRACT FROM AUTHOR]

Biocompatibility, low toxicity, ease of functionalization, ecologically sustainable synthesis, and a diverse variety of applications have all contributed to the current popularity of fluorescent carbon quantum dots (CQDs), a relatively new rising star among zero-dimensional carbon nanomaterials. However, expensive precursors and production, as well as a time-consuming procedure, frequently restrict the economic design that must be addressed. In this work, we report an economical, sustainable and green synthesis of fluorescent CQDs co-doped with N and Ca from mustard (Brassica) flower extract without the need of additional doping element precursors. The quasi-circular or polygonal shaped CQDs were revealed to be yellow-greenish fluorescent in nature with outstanding photo-stability and excellent water solubility, with an average diameter of 4.38 nm and a relative quantum yield of about 15%. The compositional analysis, crystallinity, and functional groups contained in as-synthesized N,Ca-co-doped CQDs were determined by XPS, XRD, and FTIR analysis, respectively. The presence of dominant sp3 hybridized carbons over sp2 was confirmed by 1H NMR and 13C NMR spectroscopy. The plausible fluorescence mechanisms are also proposed. Additionally, a biodegradable bioplastic derived from corn starch was used to develop an N, Ca-co-doped CQDs@bioplastic composite in order to demonstrate how it may be used to produce down-conversion light emitting diodes and optical displays. The impact of CQD concentrations and pH sensitivity were investigated further. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • We report a simple, cost-effective, eco-sustainable synthesis of fluorescent carbon quantum dots derived from precursor Cissus quadrangularis. • The as-synthesized nitrogen doped-CQDs demonstrated a homogeneous size distribution (4–9 nm), green fluorescent nature, great photo-stability, excellent water solubility, and a quantum yield of around 5 %. • A biodegradable wheat-starch-based bioplastic was employed to fabricate an N-doped CQDs@bioplastic composite to demonstrate its potential applications in quantum dot-based optical displays and down-conversion light emitting diodes. • The influence of different CQD concentrations and pH sensitivity were investigated further utilizing fabricated optical displays and LEDs. Carbon quantum dots (CQDs)-based composites as luminous down-conversion materials are becoming more popular due to several advantages such as steady fluorescence, ease of functionalization, tailoring of emission in the visible range, and so on. We report an inexpensive and environmentally sustainable synthesis of fluorescent nitrogen doped-CQDs produced from Cissus quadrangularis , a low-cost plant precursor with therapeutic value. The morphological, structural, and physicochemical features of the material were carefully investigated. Under UV stimulation (365 nm), almost spherical shaped N-CQDs with an average diameter of 5.1 nm were discovered to generate yellow-green fluorescence, have excellent photostability, and strong water solubility, with a quantum yield of up to 5 %. Furthermore, as a solid-phase dispersion matrix for CQDs, ecologically friendly and biodegradable bioplastic is appealing. The down-conversion of solid-state fluorescence of LEDs and UVC tubes was demonstrated by creating a nanocomposite by inserting N-CQDs into the solid matrix of a wheat starch-based bioplastic. Furthermore, employing constructed quantum dot-based optical displays, down-converted LEDs, and UVC tubes, the impacts of varied CQD concentrations and pH sensitivity were examined. [ABSTRACT FROM AUTHOR]

This study demonstrated an environmentally responsible, inexpensive and simple one-step hydrothermal method to synthesize biocompatible fluorescent carbon quantum dots (CQDs) from Aegle marmelos fruit extract. The near-spherical CQDs were discovered to have a naturally distributed size of 3–6 nm, were unintentionally doped with heteroatoms (Ca, K, and N) without the need for doping element precursors due to mineral contents in extract, had a quantum yield of about 4.06%, strong photostability, and excellent water solubility. Several morphological, compositional, physicochemical, and optical properties were studied. Other variables influencing CQD photoluminescence, such as hydrothermal process parameters and pH sensitivity, were also examined. Zeta potential analysis showed a negative surface charge with a zeta potential value of −5.29 mV and good dispersibility in aqueous solution. Furthermore, as an alternative to organic or synthetic probes, there is a huge need for the development of simple, affordable, and non-destructive fluorescent biomarkers. As-synthesized Ca, K, N-doped CQDs have demonstrated good fluorescent staining abilities and may be employed as a helpful probe for bio-imaging of cancer cells and other organisms. Cell survival and cytotoxicity were found to be satisfactory, with 90% of SH-SY5Y and HCT-116 cells surviving, compared to 63–77% for the other organisms, even at higher dosages (200 µg/mL) for up to 4 days. [Display omitted] • A facile heteroatom doped CQDs have been synthesized from Aegle marmelos. • Hydrothermal process dependent and pH responsive PL were examined. • Bio-imaging of cancer cells and other living organisms are demonstrated. • Cytotoxicity were found over 90% of SH-SY5Y and HCT-116 cancer cells. [ABSTRACT FROM AUTHOR]