Relaxation of the Energy of Optically Excited States in the Carbon Quantum Dots

Abstract

Recently, in connection with the achievement of new technological opportunities for fabrication nanostructured carbon-containing objects, namely, carbon quantum dots (CQDs) and clusters, studies of their various physical properties have been intensively carried out. Investigation of the photoluminescence (PL) properties of these objects have revealed a number of unique features: a wide structureless band of the radiation in the ultraviolet and visible regions of the spectrum, the fluorescent kinetics of the luminescence decay, and the independence of the long-wavelength edge of the band on the excitation quantum energy. Similar features of PL are observed early in the different nanostructured carbon-containing materials. A common structural feature of the different nanostructured carbon-containing materials, such as CQD, liquid and solid aromatic hydrocarbons, amorphous hydrogenated carbon films, natural biopolymer – collagen is the existence of carbon sextets-aromatic rings connected by Van der Waals forces. This representation of the structure made it possible in the present work to develop a dimer-excimer model of radiative processes in the CQD. The studies are related to the prospects of application due to the unique combination of a number of key properties including tunable photoluminescence, important for the development of tunable lasers, biomedical applications where photostability, biocompatibility, molecular dimensions are essential to allow chemical connection with any biomolecule without compromising its functions. Further development of the theory of PL mechanisms in the CQD can help to identify other important features of the studied objects that will be of fundamental and practical importance.