Diffusivity in water and fluorescence properties of organic nanoparticles produced in flames

Rotational and translational diffusion properties in water of nano organic carbon (NOC) particles collected from premixed laminar ethylene/air flames have been investigated using both time resolved fluorescence polarisation anisotropy (TRFPA) and fluorescence correlation spectroscopy (FCS). Insight into the NOC sizes, structures and rigidity has been gained through diffusion properties exploiting their fluorescence in different spectral ranges. The TRFPA measurements revealed the presence of two classes of particles. The first composed of particles with a mean size of 1.5 nm which absorb and fluoresce in the UV, and a second class composed of slightly larger particles, about 2.2 nm, which absorb and fluoresce in the visible and were also detected by FCS. From FCS measurements particle concentration and fluorescence quantum yield have been evaluated.