Blue Graphene Quantum Dots with High Color Purity by Controlling Subdomain Formation for Light-Emitting Devices

As an alternative to Cd-free quantum dots (QDs), graphene quantum dots (GQDs) have potential because of their various advantages, such as color tunability, nontoxicity, cost effectiveness, and photostability. However, realization of a useful blue emission from GQDs requires a narrower full width at half-maximum (FWHM) and color purity in Commission Internationale de l'Eclairage (CIE) coordinates for display applications. These emission characteristics are strongly dependent on precise control of the sp(2) C subdomain, considered as the band-gap origin of GQDs. Here, we report a preparation for blue GQDs with improved color purity obtained from KC24 graphite intercalation compounds. The as-synthesized KC24-GQD exhibits high color purity with a photoluminescence FWHM of 70 nm and CIE coordinates of (0.159, 0.082), which can be attributed to the controlled oxidation of graphene by intercalated K ions with an arrangement of KC24 surrounding seven sp(2) C hexagons favorable for the formation of uniform subdomains. Furthermore, intrinsic emission-dominant fluorescence and phosphorescence from a powdered KC24-GQD-dispersed boron oxynitride matrix, as well as from solution-based KC24-GQD, prove its applicability to various light-emitting devices.