Luminescence Mechanism of Carbon Dots by Tailoring Functional Groups for Sensing Fe3+ Ions

Abstract

In this paper, spherical carbon dots (CDs) with distinct compositions and surface states have been successfully synthesized by a facile microwave method. From the fluorescence spectra, several characteristic luminescence features have been observed: surface amino groups are dominant in the whole emission spectra centering at 445 nm, and the fingerprint emissions relevant to the impurity levels formed by some groups related to C and N elements, including C-C/C=C (intrinsic C), C-N (graphitic N), N-containing heterocycles (pyridine N) and C=O groups, are located around 305 nm, 355 nm, 410 nm, and 500 nm, respectively. Those fine luminescence features could be ascribed to the electron transition among various trapping states within the band structure caused by different chemical bonds in carbon cores, or functional groups attached to the CDs’ surfaces. According to the theoretical calculations and experimental results, a scheme of the band structure has been proposed to describe the positions of those trapping states within the band gap. Additionally, it has also been observed that the emission of CDs is sensitive to the concentration of Fe3+ ions with a linear relation in the range of Fe3+ concentration from 12.5 to 250 μM.

Recent development of carbon quantum dots regarding their optical properties, photoluminescence mechanism, and core structure

“…145 As is concluded from Yu et al's work, both surface states and carbon core are critical for the regulation of PL emission since the band gap of surface states (4.5 eV) is narrower than that of the core (5.0 eV). 163 In addition, the oxygen and nitrogen elements and related chemical bonds will produce impurity levels in the band gap, which leads to the change of excitation and emission spectra of CDs. As shown in Figure 12, there may be an energy transfer process between the carbon core and the surface state.…”

Efficient removal of Cu(ii) from aqueous systems using enhanced quantum yield nitrogen-doped carbon nanodots

“…More specically, the higher absorption peak at 284 nm conrms the energy transition from the HOMO to the LUMO originating in the carbon core (C-C and graphitic N), leading to the excitation independent emission due to the absence of multiple PL centers. 46 Meanwhile, the lower energy absorption tail is related to the transition from the HOMO to the LUMO of the surface state (pyridine N, amino N, and C]O groups). The latter can create a series of defect levels in the bandgap, resulting in the excitation dependent emission.…”

Eco-Friendly Fluorescent Carbon Nanodots: Characteristics and Potential Applications

“…The scheme of energy band structure of inner carbon core and the surface states has been depicted in Figure 2. It is Eco-Friendly Fluorescent Carbon Nanodots: Characteristics and Potential Applications DOI: http://dx.doi.org/10.5772/intechopen.89474 evident from the figure that carbon nanodots exhibit five emission bands, which have been attributed to electron transitions at intrinsic carbon (305 nm), graphitic nitrogen (355 nm), pyridine nitrogen (410 nm), amino nitrogen (455 nm), and carboxyl carbons (500 nm) [67].…”