Observation of fluorescence from non-functionalized carbon nanoparticles and its solvent dependent spectroscopy

We report solvent dependent spectroscopic study of unique non-functionalized fluorescent carbon nanoparticles (NCNPs) dispersed in 15 organic solvents: aromatic (three), hydrogen bonded (five) and aprotic (seven). Absorption spectra were found to be independent of the solvent nature, with absorption bands located around 430, 405 and 385 nm whereas photoluminescence (PL) spectra exhibited considerable solvent dependence with PL emission peaks lying in the region 405 to 500 nm. Emission life time measured by time resolved fluorescence spectroscopy revealed that in aromatic solvents the average lifetime (τav), did not change significantly with solvent polarity, which was, typically 4–5 ns under the excitation of 405 nm. In hydrogen bonded solvents, τav was observed to decrease with solvent polarity, but in case of aprotic solvents, τav was observed to increase with solvent polarity for a particular excitation. Emission data in hand revealed possible quantum confinement of these nanoparticles inside the cavity of rings of THF, p-xylene, benzene and toluene molecules.