Abstract
Unexpectedly bright photoluminescence emission can be observed in materials incorporating inorganic carbon when their size is reduced from macro–micro to nano. At present, there is no consensus in its understanding, and many suggested explanations are not consistent with the broad range of experimental data. In this Review, I discuss the possible role of collective excitations (excitons) generated by resonance electronic interactions among the chromophore elements within these nanoparticles. The Förster-type resonance energy transfer (FRET) mechanism of energy migration within nanoparticles operates when the composing fluorophores are the localized electronic systems interacting at a distance. Meanwhile, the resonance interactions among closely located fluorophores may lead to delocalization of the excited states over many molecules resulting in Frenkel excitons. The H-aggregate-type quantum coherence originating from strong coupling among the transition dipoles of adjacent chromophores in a co-facial stacking arrangement and exciton transport to emissive traps are the basis of the presented model. It can explain most of the hitherto known experimental observations and must stimulate the progress towards their versatile applications.
Highlights
Serendipitous discovery of the photoluminescent properties of carbon nanoparticles [1,2] took researchers by great surprise
It can be observed that hundreds and even thousands of publications with their exponential growth in recent years still have not provided a consistent view of the origin of emission of carbon nanomaterials. This hinders significantly the development of new materials with desirable characteristics and their efficient use. The goal of this Review was to provide a broad view of the physical mechanisms responsible for the fluorescence of carbon nanoparticles based on collective excitonic effects
This Review focused on the possibility of the formation and propagation of Frenkel excitons, i.e., the quantum coherent excitations that spread over the whole nanoparticle or its significant part performing as a system of organized interacting fluorophores
Summary
Serendipitous discovery of the photoluminescent properties of carbon nanoparticles [1,2] took researchers by great surprise. Despite strong variability in size, composition, structural order, solubility, and other reported parameters, the photophysical and spectroscopic properties of these new emitters demonstrated some general features [11,12] These features turned out to be quite different from those observed in organic dye molecules [13] or nanoparticles of inorganic origin such as semiconductor quantum dots [14]. This hinders significantly the development of new materials with desirable characteristics and their efficient use The goal of this Review was to provide a broad view of the physical mechanisms responsible for the fluorescence of carbon nanoparticles based on collective excitonic effects. I believe that such a platform will allow for the creation of new steps for a better understanding of the unique features of these nanoscale systems
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