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.

Sustainable, inexpensive, and environmentally friendly biomass waste can be exploited for large‐scale production of carbon nanomaterials. Here, alkali lignin was employed as a precursor to synthesize carbon quantum dots (CQDs) with bright green fluorescence through a simple one‐pot route. The prepared CQDs had a size of 1.5–3.5 nm, were water‐dispersible, and showed wonderful biocompatibility, in addition to their excellent photoluminescence and electrocatalysis properties. These high‐quality CQDs could be used in a wide range of applications such as metal‐ion detection, cell imaging, and electrocatalysis. The wide range of biomass lignin feedstocks provide a green, low‐cost, and viable strategy for producing high‐quality fluorescent CQDs and enable the conversion of biomass waste into high‐value products that promote sustainable development of the economy and human society.

A dual-mode colorimetric/fluorescence pH sensor was fabricated from carbon dots (CDs). It exhibited a pH response via both fluorescence and visible colorimetric observation. The CDs solution changed from red to yellow when the pH changed from acid to alkaline. Meanwhile, the color of pH test paper that incorporated the CDs changed from purple-red to orange and then to yellow. The CD fluorescence maximum was at 630 nm in acid solution and 590 nm under neutral and alkaline conditions. The fluorescence of the pH test paper changed from red to orange and then to yellow, which was better than that of the pure CDs solution. The CDs exhibited highly selective and reversible fluorescence quenching with respect to Cu 2+ ions because of strong binding and fast chelating kinetics. There was a linear relationship between fluorescence quenching and Cu 2+ concentration, suggesting the other promising practical usage of this sensing system. The versatile CDs-based pH sensor thus provides a basis for developing sustainable and fast-response dual-mode pH meters as well as Cu 2+ sensing.

Here we introduce a simple, superfast, and scalable strategy that obtains graphene quantum dots (GQDs) within 3 min under microwave irradiation (MA-GQDs). The MA-GQDs exhibit excellent fluorescence quantum yields up to 35% in the optimum reaction condition. The MA-GQDs with single-crystalline and few-layer structure can reach the visible region with the longest absorption wavelength at 700 nm. Moreover, these ultrabright-fluorescence and stable MA-GQDs as a phosphor and fluorescence probe could be efficiently applied in white light-emitting diodes and cell-imaging fields. The developed pathway to GQDs can provide unambiguous and remarkable insights into the design of high-fluorescence and few-defect GQDs, and expedite the applications of GQDs.

Room-temperature phosphorescent (RTP) carbon dots (CDs) have been fascinated by a lot of scholars because of their stable triplet excited states and environmental friendliness. Herein, novel fluorescent oxygen-enriched CDs were synthesized by a simple one-step solvothermal approach, which can be applied in cell imaging directly as a nontoxic fluorescent probe. When mixing the CDs with polyvinyl alcohol, the composite exhibits excellent RTP performance, which has the exciting prospect of applications in security protection. The observed RTP is attributed to the lone pair electrons provided by oxygen-rich functional groups of CDs. Benefitting from the n → π* transition and triplet exciton filling, the C−O−C groups of CDs play a significant role in their ultralong RTP performance. Our finding creates an avenue for advanced security protection technology based on metal-free RTP carbon nanomaterials.