In recent years, various nanostructures of carbon have drawn a lot of interest in research because of their potential applications in optoelectronics, biology, mechanical hardening, electrical conductivity etc. They have good bio-compatibility, synthesis methods are relatively cheap, and precursors are mostly eco-friendly. In 2004, discovery of highly luminescent nanoparticles of carbon referred as carbon dots (CDs) led to a new direction of exploration for optoelectronic and imaging applications. A CD typically consists of a carbon core and surface structure having functional groups such as amine, carboxyl groups etc., depending on the synthesis process and the precursors. Based on the core structure, they can be broadly classified in to four different types: graphene quantum dots (core is made of single or few layers of graphene), carbon quantum/nano dots (core is made of sp2/sp3 hybridised carbon atoms) and carbon polymer dots (core is made of a polymer/carbon hybrid structures).
We will investigate the optical properties of the CDs and perform a systematic study on their dependence on the synthesis parameters. The aim is to fabricate CDs with high luminescence efficiencies with tunable emission wavelength. We will also investigate the fundamental mechanisms involved in the optical emission of these dots, which are still unclear. The CDs show PL features which can be excitation wavelength dependent or independent determined by the source of the emission which is currently a topic of controversy. We will perform time resolved studies to understand the carrier and energy exchanges happening between various levels within the dot that will shed light on the processes involved. To understand the role played by the size of the dot, core and the surface ligands on the emissive properties, we will perform DFT simulations using commercial software, before attempting fabrication of such CDs. Optimization of synthesis process and post growth functionalization will allow tuning of the PL of CDs, which will then be incorporated as an active layer in LEDs and also explored for encoding applications. Results of preliminary work on synthesis of CDs and photoluminescence studies will be presented in the seminar.