Correlations between structure and photoluminescence properties in N-doped carbon nanoparticles

Carbon nanoparticles (CNPs) have received great attention because of their unique optical and electronic properties. To modulate their photoluminescence properties, nitrogen doping has been previously reported, but it was difficult to find correlations between the photoluminescence properties and the nanoparticle structure. For this purpose, we analyzed the effect of the chemical composition and the particle size on the photoluminescence of N-doped carbon nanoparticles (NCNPs) obtained by the acidic treatment of different starting materials. However, the use of different precursors introduced a high degree of heterogeneity in the nanoparticle structure, which hindered the interpretation of the photoluminescence results. To minimize these effects, in this work we have selected the hydrothermal treatment of the graphene oxide (GO) and urea by modifying the urea: GO mass ratio. Our results show the existence of four emissive centers assigned to π→π∗ transition for aromatic domains in zigzag and armchair configurations, charge-transfer, and n→ π∗ transitions. We also report linear correlations between the charge-transfer and n → π∗ emissions and the percentage of pyrrolic and pyridinic N-groups. Besides, we show that the charge-transfer emission is quenched by the carbonyl groups at the basal plane of the nanoparticles.