title: Molecular origin of photoluminescence of carbon dots: aggregation-induced orange-red emission.
abstract: The molecular origin of the photoluminescence of carbon dots (CDs) is not known. This restricts the design of CDs with desired optical properties. We have synthesized CDs starting from carbohydrates by employing a simple synthesis method. We were able to demonstrate that the CDs are composed of aggregated hydroxymethylfurfural (HMF) derivatives. The optical properties of these CDs are quite unique. These CDs exhibit an excitation-independent PL emission maximum in the orange-red region (λ ∼ 590 nm). These CDs also exhibit excitation as well as monitoring wavelength-independent single exponential PL decay. These observations indicate that only one type of chromophore (HMF derivative) is present within the CDs. Several HMF derivatives are aggregated within the CDs; therefore, the aggregated structure cause a large Stokes shift (∼150 nm). By several control experiments, we showed that the same aggregated chromophore unit (HMF derivative), and not the individual fluorophores, is the fluorescing unit. The emission maximum and the single exponential PL lifetime are independent of the polarity of the medium. The existence of a low-lying trap state could be reduced quite significantly. A model has been proposed to explain the interesting steady state and dynamical photoluminescence behaviour of the CDs. As the molecular origin of their photoluminescence is known, CDs with desired optical properties can be designed.
authors.affiliation: Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur, West Bengal 741246, India. prasunchem@iiserkol.ac.in.
authors.forename: Venkatesh
authors.initials: V
authors.lastname: Gude
authors.affiliation: Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur, West Bengal 741246, India. prasunchem@iiserkol.ac.in.
authors.forename: Ananya
authors.initials: A
authors.lastname: Das
authors.affiliation: Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur, West Bengal 741246, India. prasunchem@iiserkol.ac.in.
authors.forename: Tanmay
authors.initials: T
authors.lastname: Chatterjee
authors.affiliation: Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur, West Bengal 741246, India. prasunchem@iiserkol.ac.in.
authors.forename: Prasun K
authors.initials: PK
authors.lastname: Mandal