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.
Highlights
As an emerging new class of nanomaterials, carbon dots have attracted much research interest recently due to their unique optical properties, abundant raw materials, simple preparation methods, basically non-toxic, good biocompatibility, and easy surface modification [1,2,3]
The size and morphology of the synthesized carbon dots (CDs) have been characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM)
Through using various amino acids as raw materials, the carbon and nitrogen compositions and related chemical bonds have been carefully controlled in order to modulate the luminescence from diffrent trapping states within the band structure of CDs
Summary
As an emerging new class of nanomaterials, carbon dots have attracted much research interest recently due to their unique optical properties, abundant raw materials, simple preparation methods, basically non-toxic, good biocompatibility, and easy surface modification [1,2,3] Since their discovery, CDs have been applied in various technical fields, such as bio-imaging [4,5], light emitting diodes [6,7], photo-catalysts [8,9], anticancer drug delivery [10,11], chemical sensors (metal ions [12,13] or organics [14] detection), and so on. It is of great importance to find an efficient way to separate each chemical state and describe their possible positions within the band structure in order to clarify the characteristic luminescence features in photoluminescence spectra
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