Synthesis of Carbon Dots with Multiple Color Emission by Controlled Graphitization and Surface Functionalization

TLDR

Multiple‑color‑emissive carbon dots hold promise for bioimaging, light‑emitting devices, and photocatalysis, yet most reported dots exhibit excitation‑dependent emissions limited to the blue region. The study reports a synthesis of multi‑color‑emissive carbon dots via controlled graphitization and surface functionalization. The dots are produced by thermal pyrolysis of citric acid and urea, with emission tuned from 430 to 630 nm by adjusting graphitization extent and surface COOH groups. By varying pyrolysis temperature and reactant ratio, the dots’ emission shifts from blue to red across the spectrum, achieving quantum yields up to 52.6 % (blue), 35.1 % (green), and 12.9 % (red), and enabling uniform dispersion in epoxy for transparent, multi‑color and white‑light emitting devices, positioning them as low‑cost phosphor alternatives.

Abstract

Abstract Multiple‐color‐emissive carbon dots (CDots) have potential applications in various fields such as bioimaging, light‐emitting devices, and photocatalysis. The majority of the current CDots to date exhibit excitation‐wavelength‐dependent emissions with their maximum emission limited at the blue‐light region. Here, a synthesis of multiple‐color‐emission CDots by controlled graphitization and surface function is reported. The CDots are synthesized through controlled thermal pyrolysis of citric acid and urea. By regulating the thermal‐pyrolysis temperature and ratio of reactants, the maximum emission of the resulting CDots gradually shifts from blue to red light, covering the entire light spectrum. Specifically, the emission position of the CDots can be tuned from 430 to 630 nm through controlling the extent of graphitization and the amount of surface functional groups, COOH. The relative photoluminescence quantum yields of the CDots with blue, green, and red emission reach up to 52.6%, 35.1%, and 12.9%, respectively. Furthermore, it is demonstrated that the CDots can be uniformly dispersed into epoxy resins and be fabricated as transparent CDots/epoxy composites for multiple‐color‐ and white‐light‐emitting devices. This research opens a door for developing low‐cost CDots as alternative phosphors for light‐emitting devices.