Influence of particle size of flame-synthesized carbon nanoparticles on band gap and photoluminescence properties.

Band gap and photoluminescence (PL) properties were investigated for flame-synthesized carbon nanoparticles (CNPs) of four different particle size distributions. The particles were collected by varying the flow rates of fuel and oxidizer in a controllable co-flow diffusion flame. The results indicated the possibility of both direct and indirect band gaps in the synthesized CNPs. The band gaps were found to increase with a decrease in the particle size, thereby exhibiting the quantum confinement effect. The PL properties observed with the pure powdered sample showed strong emission in the green region. However, for samples dispersed in isopropyl alcohol, the emission wavelength shifts towards the blue region, showing strong solvent dependence. The particle size of CNPs, however, only affects the emission peak intensities.