Time-resolved spectroscopy of the ensembled photoluminescence of nitrogen- and boron/nitrogen-doped carbon dots.

Carbon dots (CDs) have potential applications in various fields such as energy, catalysis, and bioimaging due to their strong and tuneable photoluminescence (PL), low toxicity, and robust chemical inertness. Although several PL mechanisms have been proposed, the origin of PL in CDs is still in debate because of the ensembled nature of the heterogeneous luminophores present in the CDs. To unravel the origin of PL in CDs, we performed time-resolved spectroscopy on two types of CDs: nitrogen-doped (N-CD) and boron-nitrogen co-doped (BN-CD). The PL decays were fitted by stretched exponential functions to estimate the distribution of the decay kinetics in the CDs, which have different PL lifetime distributions. Both CDs displayed main, blue emission decaying in 15 ns, which originates from the dominant molecular state. The analysis of the non-exponential PL decay using stretched exponential fits revealed that the functional surface luminophores are of less variety but of more environmental heterogeneity and have much lower populations in BN-CD than in N-CD.

Morphology Tunable Hybrid Carbon Nanosheets with Solvatochromism.

The tunable photoluminescence of carbon-based nanomaterials has received much attention for a wide range of applications. Herein, a unique, broad-solvatochromic hybrid carbon nanosheet (CNS) synthesized through the hydrothermal carbonization of molecular precursors exploiting graphene oxide as a template is reported, resulting in the formation of clusters of carbon nanorings on the surface of graphene-oxide nanosheets. Under UV and visible-light excitation, the hybrid CNS exhibits tunable emission spanning the wide range of colors in a series of solvents with different polarities. This interesting spectroscopic behavior is found to originate from hydrogen-bonding interactions between CNS and solvents, which eventually induce the morphological transition of CNS from 2D sheets to 3D crumpled morphologies, affecting the lifetimes of emissive states. This novel soft carbon nanostructure may open up a new possibility in tailoring the photophysical properties of carbon nanomaterials.