Title: Photoluminescence of carbon nanoparticles synthesized by laser ablation in water and aqueous solutions of amine-based reagents

Abstract

The comparison between two synthesis routes for obtaining carbon nanoparticles (CNPs) in water and in aqueous solutions of amine based reagents is presented. The influence of synthesis approach and parameters on structural and luminescent properties of CNPs is discussed. Each of the synthesis routes was a two-step process. In the first approach, the graphite target submerged in water was ablated using moderate fluence of a laser beam. Next, a certain amount of aqueous reagent solution was added to the suspension of carbon particles. Such a mixture was then exposed to a much stronger laser beam in order to reduce the size of particles. In contrast to the first approach, during another synthesis route the graphite target was immersed in aqueous reagent solution and exposed to laser irradiation. The obtained suspension of carbon nanoparticles was further irradiated without the presence of graphite target. Luminescence and absorbance studies revealed interesting properties of obtained colloids. Suspension of particles produced in pure water after first step is yellowish and has some absorbance in whole spectrum rising as the wavelength decreases. After second step it is colourless and fully transparent in visible light and has high absorbance in UV with distinct maximum about 285 nm. The addition of the reagent at the second step of the synthesis leads to location of absorbance maximum at about 285 nm. However, using amine-based solution from the beginning causes high absorbance in the whole spectrum without any distinctive maximum. It may indicate the simultaneous creation of different carbon structures and fluorescent molecules during laser ablation process.