Nature of photoexcited states in ZnO-embedded graphene quantum dots

TL;DR

This study theoretically investigates ZnO-embedded graphene quantum dots, revealing how ZnO content influences their structure, stability, and light absorption, with potential implications for optoelectronic applications.

Contribution

The paper introduces a theoretical design and analysis of novel ZnO-embedded graphene quantum dots, providing insights into their structure, stability, and excited state properties.

Findings

Strong dependence of properties on ZnO content

Enhanced light absorption in highly symmetric systems

Deep understanding of excited state nature

Abstract

The combination of wide-band gap semiconductors like zinc oxide (ZnO) and graphene quantum dots (GQDs) is a promising strategy to tune optoelectronic properties of GQDs and to develop new functionalities. Here we report on a theoretical design of not-yet-synthesized hybrid materials composed of ZnO clusters surrounded by carbon moieties, hereinafter referred to as ZnO-embedded graphene quantum dots. Their structure and light absorption properties are presented, with an in-depth analysis of the nature of the photoexcited states. The stability of the (ZnO)nC96-2n system with n=1, 3, 4, 7, 12 and 27 is investigated by estimating cohesive energy and performing vibrational mode analysis. A strong dependence of the structural and optoelectronic properties of the hybrid material on the amount of ZnO pairs is revealed and discussed. A strong light absorption and unexpected enhancement of Raman modes related to the vibrations in carbon moiety are observed for highly symmetric (ZnO)27C42 system that makes it an ideal study subject. Complementary excited state analysis, charge density difference (CDD) analysis and interfragment charge transfer analysis enabled reaching deep insights into the nature of the excited states. A dominating contribution of doubly degenerate locally excited states in broadband light absorption by (ZnO)27C42 is identified. The present results are helpful to elucidate the nature of the fundamental internal mechanisms underlying the light absorption in ZnO-embedded graphene quantum dots, thereby providing a scientific background for future experimental study of low-dimensional metal-oxygen-carbon materials family.