Electron spin dynamics in sucrose-derived luminescent carbon dot-silica nanocomposites

Abstract

In the present work, a bottom-up approach to synthesize luminescent carbon dot-silica (CDs@SiO2) nanocomposites from the sucrose precursor was utilized. The sucrose concentration and thermal treatment effect on electron spin dynamics in CDs@SiO2 nanocomposites was investigated by electron spin resonance (ESR) technique. A single ESR line resulting from exchange interaction between localized and non-localized electrons was observed. The non-localized electrons were related to carbon-related radicals in the sp3-hybridized state, while the carbon dots (CDs) act as localized electrons. The observed narrowing of the exchange ESR line with temperature rise was explained by a combination of Anderson's spin-exchange motional narrowing and a hopping wave function. The high conductivity of the material is evidenced by the Dysonian lineshape of the ESR signal. The relation between CDs size and conductivity of the CDs@SiO2 nanocomposites was found. The metallic character of the CDs@SiO2 conductivity was explained by the quantum size effect that occurred due to the reaggregation of the CDs. It was concluded that the previously observed shift of photoluminescence (PL) band and further quenching of PL with the increase of sucrose concentration in CDs@SiO2 is caused by the quantum size effect.