From highly graphitic to amorphous carbon dots: A critical review
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REVIEW From highly graphitic to amorphous carbon dots: A critical review
Antonios Kelarakis, Centre for Materials Science, School of Forensic and Investigative Sciences, University of Central Lancashire, Preston PR12HE, United Kingdom Address all correspondence to Antonios Kelarakis at [email protected] (Received 26 February 2014; accepted 30 April 2014)
ABSTRACT Graphitic and amorphous C-dots share common characteristics in their photoluminescence behavior. However, the graphitic dots have a lead as electrocatalyst for fuel cells, sensitizers, and electron acceptors for solar cells. The emergence of carbogenic nanoparticles (C-dots) as a new class of photoluminescent (PL) nanoemitters is directly related to their economical preparation, nontoxic nature, versatility, and tunability. C-dots are typically prepared by pyrolytic or oxidative treatment of suitable precursors. While the surface functionalities critically affect the dispersibility and the emission intensity of C-dots in a given environment, it is the nature of the carbogenic core that actually imparts certain intrinsic properties. Depending on the synthetic approach and the starting materials, the structure of the carbogenic core can vary from highly graphitic all the way to completely amorphous. This critical review focuses on correlating the functions of C-dots with the graphitic or amorphous nature of their carbogenic cores. The systematic classification on that basis can provide insights on the origins of their intriguing photophysical behavior and can contribute in realizing their full potential in challenging applications. Keywords: luminescence; nanostructure; carbonization
DISCUSSION POINT ▪ C-dots set an example that low-cost, non-toxic materials can effectively supplant highly engineered, yet toxic compounds in challenging applications.
Introduction The emergence of carbogenic nanoparticles (otherwise known as C-dots) as a new class of photoluminescent (PL) nanoemitters has led to worth mentioning paradoxes about the fascinating story of molecular carbons. First, it is the realization that those nanoparticles are abundant in the planet (in the form of tiny graphitic fragments or combustion products), but they have gone unnoticed until recently. Chronologically, the first observation of C-dots1 falls close to the isolation of graphene by mechanical exfoliation,2 but those ground-breaking advances only took place few years after the development of fullerenes3 and carbon nanotubes4 (CNTs). Second, it is the realistic perspective that those, oftentimes naturally or incidentally occurring nanoparticles (Fig. 1), can
adequately replace highly engineered semiconductor emitters (commonly referred as heavy metal-based quantum dots) in demanding applications where extensive optical absorption, excitation wavelength-dependent emission, multiphonon excitation, and upconversion are needed. While ultra-long, defect-free graphene sheets are ideal for electronics, the exact opposite features, e.g., surface defects and fragmentation, seem to be a precond
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