It is demonstrated that treatment of blue‐emissive carbon dots (CDs) with aqueous hydrogen peroxide (H2O2) results in the green emissive solid state CD phosphor with photoluminescence quantum yield of 25% and short luminescence lifetime of 6 ns. The bathochromic‐shifted, enhanced green emission of H2O2‐treated CDs in the powder is ascribed to surface state changes occurring in the aggregated material. Using the green emissive H2O2‐treated CD phosphor, down‐conversion white‐light‐emitting devices with cool, pure, and warm white light are fabricated. Moreover, using the green emissive CD phosphor as a color converter, a laser‐based white‐light source is realized, and visible light communication with a high modulation bandwidth of up to 285 MHz and data transmission rate of ≈435 Mbps is demonstrated.

On/off switching of the phosphorescence signal is realized in a composite carbon dot/polyvinyl alcohol material via thermal annealing, water spraying, and 1532 nm laser writing, respectively, which provides a new route to multiple data encryption.

A co-crystallization strategy with cyanuric acid to modulate the bandgap emissions of CDs was realized to produce highly emissive solid composite CD-based materials.

A composite phosphor comprising carbon dots and g-C3N4 is prepared on a large scale through a green microwave assisted in situ heating method, and is used for fabrication of white LEDs with a power efficiency of up to 42 lm W−1.

Carbon quantum dots (CQDs) with excellent properties have attracted attention owing to wide applications in many fields. In this paper, we report a method to synthesize CQDs at room temperature without any external energy supply and energy-catalyzing reagents. The characterization results indicate that the CQDs have good dispersion and water solubility, the averaged dimension is around 5.37 nm, consisting mainly of C, O, N, and S elements, the fluorescence quantum yield was 8.72%. In addition, the experimental results show that CQDs have excellent optical stability and good biocompatibility, which can be used in the field of cellular imaging