Influence of size and composition on fluorescence from carbonaceous nanoparticles

Abstract

In this paper, we have separated two spherical carbonaceous nanoparticles (CNPs) by centrifuge-filtration synthesized from glucose and urea using hydrothermal method. The separated CNPs, CNP-1(13 ± 4 nm) and CNP-2 (33 ± 3 nm) have narrow size distributions. Since they are synthesized by the same method, their composition was similar except in O content. The fluorescence quantum yields and lifetimes of the CNPs were measured. The fluorescence quantum yield of CNP-1 is low (0.005 ± 0.002) due to higher oxygen content compared to that of CNP-2 (0.011 ± 0.003) with lower oxygen content. The CNPs display excitation wavelength dependent emission properties and their lifetimes were fitted to bi-exponentials. The two lifetimes for both the particles are fast showing that nonradiative pathway for relaxation is significant in the CNPs. The fluorescence lifetimes were also composition and size dependent. The size of the particles was large enough for quantum confinement effects not to influence the emission properties. Surface trapped states coupled to n-π* transitions centered on the N and O containing surface functional groups are responsible for the fluorescence behavior of the CNPs.