(Invited) Emission Origin of Lowly-Oxidized Graphene Quantum Dot Toward Light Emitting Devices

Abstract

Graphene quantum dots (GQDs), simply making graphene typically under 10 nm, and the change of emission behavior from known fluorescence on graphene draws huge interest for potential applications to display, lighting, and optoelectronic devices. GQD could be a new class of optical material with useful properties of tunable luminescence, low cost, and superior photo and chemical stability. Our group has developed unique exfoliation and dispersion methods of 2D materials by the intercalation of alkali metal/organics. With the advantage of the methods generally excluding, or controlling, the oxidation of 2D materials, we have studied the origin of intrinsic emission (~ 400 nm) of graphene in depth. With those samples, I will introduce the role of oxidation in GQDs which forms isolated small sp2 carbon hexagons within a GQD, known as subdomains. Experimental evidences supported with calculation of the formation energy of subdomains and bandgap will give a guideline to improve emission properties. With those understanding the first demonstration of GQD light-emitting diodes (GQD-LEDs) with 1,000 cd/m2, alternating current powder elctroluminescence (ACPEL) device, and GQD phosphorescence for security application promise the optical applications of 2D materials with further improvement.