Characterization of ultrafast fluorescence from nanometric carbon particles

We present two distinct implementations of the time resolved fluorescence polarization anisotropy ( TRFPA) technique for the analysis of carbon nanoparticles collected from laminar laboratory flames and from the exhaust of a gasoline vehicle engine. By exploiting the high time-resolution and the spectral resolution of our TRFPA setups, we could identify two groups of particles, with diameter of 1.4 and 2.2 nm, respectively, within the laminar flame sample. On the other hand, the high time-resolution TRFPA analysis of the gasoline sample led to the identification of two distinct decay channels. The slower one was consistent with a single kind of small particle with diameter of 1.3 nm. Moreover, an analysis of the fast decay versus the temperature allowed us to rule out that it was due to the presence of lighter particles within the sample. Most likely, it is related to the relaxation of internal degrees of freedom.