Despite many efforts, the mechanisms of light absorption and emission of small fluorescent carbon nanoparticles (C-dots) are still unresolved and are a subject of active discussion. In this work we address the question as to whether the fluorescence is a collective property of these nanoparticles or they are composed of assembled individual emitters. Selecting three types of C-dots with “violet”, “blue” and “green” emissions and performing a detailed study of fluorescence intensity, lifetime and time-resolved anisotropy as a function of excitation and emission wavelengths together with the effect of viscogen and dynamic fluorescence quencher, we demonstrate that the C-dots represent assemblies of surface-exposed fluorophores. They behave as individual emitters, display electronic anisotropy, do not exchange their excited-state energies via homo-FRET and possibly display sub-nanosecond intra-particle mobility.

The influence of the co-doping of cerium-doped lutetium oxyorthosilicate (LSO) with ytterbium on the output characteristics of this scintillator material were investigated by studying X-ray luminescence spectra, emission decay kinetics, afterglow level, Vickers indentation hardness, thermally stimulated luminescence, and radiation stability of luminescence parameters. It has been demonstrated that the optimal doping contents are ~ 0.1 mol.% and ~ 0.5 mol.% for cerium and ytterbium, respectively. A considerable increase in the radiation stability of light output, decrease in the afterglow level by more than two orders of magnitude and a 20% decrease in indentation hardness at the optimal concentration of Yb have been observed, however, at the expense of the light output.