Blue-Green Electroluminescent Carbon Dots Derived from Fenugreek Seeds for Display and Lighting Applications

Natural product-derived carbon dots (CDs) have been widely studied as environmentally friendly materials for various applications, such as for bioimaging and as sensors, catalysts, and solar cells. Electroluminescence (EL) is one of the most desirable characteristic of CDs for optical devices in display and lighting applications. EL devices with CDs possess a layered structure, in which CDs serve as a middle emission layer sandwiched by transport layers and electrodes. Electrons and holes are injected into the active CD emission layer by an external bias voltage and give rise to EL through radiative recombination. However, the EL of natural product-derived CDs has not been achieved yet owing to issues such as difficulty of mass production and quenching in a dry state. Here, we report for the first time the EL of natural product-derived CDs, which were synthesized from fenugreek seeds via an easy single-step pyrolysis process. The CDs were highly dispersible in solvents and could thus be used as an emissive layer in a light-emitting diode by spin-coating a highly concentrated CD solution between the organic hole and electron transport layers on an indium tin oxide-coated glass substrate. The CDs maintained sufficient dispersion and emissive yields in both the solution (ethanol) and dry states. Furthermore, the LED comprising the CDs exhibited blue-green EL with a spectral peak at 507 nm and maximum luminance of 115.4 cd m(-)(2). The value of luminance is comparable with that of EL from some CDs synthesized from a chemical carbon source. Our results highlight the great potential of natural product-derived CDs as an environmentally friendly material for LEDs.