Photoluminescent Carbon Nanostructures

Photoluminescent nanosized allotropes of carbon have attracted considerable interest because of their diverse optical properties depending on their crystal structure, size, and morphology, and chemical functionalization. Here, we present the first critical review covering the photoluminescence (PL) properties, their control, and origin in various carbon allotropes and their composites. Different mechanisms by which carbon nanostructures exhibit PL are discussed, involving excitonic PL in carbon nanotubes, thermally activated delayed fluorescence in spherical fullerenes, the presence of impurity vacancy color centers in nano diamonds, aromatic sp(2) domains in reduced graphene oxide, and surface chromophores or defect-related PL in carbon dots. We critically analyze the intrinsic and external effects affecting the PL properties (spectral shift, decay, quantum yield) from both experimental data and theoretical calculations: The key parameters addressed include, for example, the type and content of impurity elements in nanodiamonds (NV and SiV centers), chemical composition in reduced graphene oxides, external effects (temperature, solvent) in C-60 fullerene, structural type (single-wall versus multi-wall carbon nanotubes), and the roles of doping and surface functional groups in the PL behavior of carbon/graphene dots.