White‐light‐emitting carbon dots (WCDs) show innate advantages as phosphors in white light‐emitting diodes (WLEDs). For WLEDs, the color rendering index (CRI) is the most important metric to evaluate its performance. Herein, WCDs are prepared by a facile one‐step solvothermal reaction of trimellitic acid and o‐phenylenediamine. It consists of four CDs identified by column chromatography as blue, green, yellow, red, and thus white light is a superposition of these four types of light. The mixture of the four CDs undergoes Förster resonance energy transfer to induce the generation of white light. The photoluminescence of WCDs originates from the synergistic effect of carbon core and surface states. Thereinto, the carbon core states dominate in RCDs, and the increase of amide contents and degree of conjugation promote the redshift of the emission spectra, which is further confirmed by theoretical calculations. In addition, a high CRI of 97 is achieved when the WCDs are used as phosphors to fabricate WLEDs, which is almost the highest value up to now. The multicolor LEDs can also be fabricated by using the four multicolor CDs as phosphors, respectively. This work provides a novel approach to explore the rapid preparation of low‐cost, high‐performance WCDs and CDs‐based WLEDs.

Photoluminescent organosilane-functionalized carbon quantum dots (CQDs), 3.0–3.5 nm in diameter, were synthesized via a facile hydrothermal method using citric acid monohydrate as a precursor and N-(3-(trimethoxysilyl) propyl) ethylenediamine as a coordinating and passivation agent. The optical properties of the as-obtained CQDs were investigated in detail. The CQD aqueous solution emits bright blue-white light under ultraviolet (UV) illumination with a quantum yield of 57.3% and high red-green-blue (RGB) spectral composition of 60.1%, and in particular the CQDs exhibit excitation-independent photoluminescence. The CQDs have a narrow size distribution around 3.1 nm and good film-forming ability through simple heat-treatment. By virtue of these excellent optical characteristics and good film-forming ability, a white light-emitting device (LED) was fabricated by combining a UV-LED chip with a single CQD phosphor film, which exhibited cool white light with a CIE coordinate of (0.31, 0.36), a color rendering index of 84 and a correlated color temperature of 6282 K. In addition, the white LED exhibits good optical stability under various working currents and for different working time intervals. Moreover, the interaction between the carbogenic core and surface groups was discussed using the DMol³ program based on density functional theory. This research suggests the great potential of CQDs for solid-state lighting systems and reveals the effect of the surface state on the photoluminescent mechanism of CQDs.

Highly fluorescent water-soluble and nitrogen-doped carbon dots (NCDs) were synthesized by a simple one-pot hydrothermal method using citric acid as carbon source and urea as nitrogen source. Quantum yield of NCDs reaches 42.2%. As-obtained NCDs show a strong emission at 440 nm with an optimum excitation at 355 nm, and exhibit high photostability and excitation-independent photoluminescence (PL) behavior under excitation at 240–380 nm. However, such NCDs show excitation-dependent PL behavior under excitation of 380–480 nm. Because of the Hg²⁺-induced fluorescence quenching of carbon dots (CDs), such NCDs can be used as an effective fluorescent nanoprobe for highly selective and sensitive detection of Hg²⁺ in aqueous solution, with a limit of detection (LOD) as low as 2.91 nM in a linear range of 0–50 nM. The NCDs offer a rapid detection of Hg²⁺ with one-step rapid operation within 5 min. Further, as-prepared NCDs also exhibit high sensitivity towards Hg²⁺ in tap water and mineral water samples. The linear ranges of detection are both 0–50 nM. The LODs in tap water and mineral water samples are as low as 2.88 nM and 2.87 nM, respectively.

A one-pot microwave-assisted hydrothermal approach was developed to quickly synthesize organosilane-functionalized carbon dots (Si-CDs) within 5 minutes. With the assistance of N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane (KH-792) as distance barrier chains, aggregation-caused quenching is suppressed successfully, which contributes to the emission of bright blue fluorescence by solid-state Si-CDs (λ_em ∼ 454 nm). The photoluminescence quantum yield of the as-prepared Si-CDs in the solid state reaches 65.8% with an optimized molar ratio of the reactant citric acid to KH-792 of 1 : 5 and a reaction temperature of 180 °C, which is 2.5-fold that of their solution. Together with their good film-forming ability and thermal stability, Si-CDs were applied to fabricate a white-light-emitting device with color coordinates of (0.32, 0.36) and a correlated color temperature of 6071 K. Our results indicate that the as-prepared Si-CDs are promising materials with efficient solid-state emission to be used in lighting, backlight displays and other optoelectronic devices.