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

N.K Saitova,S.E Kumekov

doi:10.18321/ectj723

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 longwavelength 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.

Highlights

The increased interest in the study of photoluminescence (PL) in carbon quantum dots (CQD) is associated with a fundamental interest in their possible applications in solar energy, biotechnology, medicine, and nanoelectronic devices [1]
Various methods have been developed for the fabrication of CQDs based on graphene, graphite, and polymers [2]
In the literature [9] different mechanisms of PL in the CQD were discussed: the quantum size effect, fluorophores with various degrees of π ‒ conjugation, recombination of electron-hole pairs localized within small sp2 carbon clusters embedded within a sp3 matrix, defects and surface states, surface groups, and surface passivation

Summary

Introduction

The increased interest in the study of photoluminescence (PL) in carbon quantum dots (CQD) is associated with a fundamental interest in their possible applications in solar energy, biotechnology, medicine, and nanoelectronic devices [1]. Collagen contains in its structure chromophore aromatic amino acids, which allowed the authors [13] to explain the features of PL based on the excimer model. The sign of the Coulomb interaction is different for the ground state of the dimer and the excited state of the dimer (excimer).

Results

Conclusion