Luminescent Carbon Dots Synthesized by the Laser Ablation of Graphite in Polyethylenimine and Ethylenediamine

Abstract

Fluorescent carbon dots (CDs) synthesized by pulsed laser ablation in liquid (PLAL) are still interesting materials due to their possible applications. However, unlike CDs produced by the hydrothermal method, CDs produced the synthesis products by the PLAL method were never separated by dialysis, which differentiates the synthesis products and allows the identification of the main source of fluorescence. In this work, the synthesis of fluorescent carbon dots (CDs) was performed by nanosecond laser ablation of a graphite target immersed in polyethyleneimine (PEI) and ethylenediamine (EDA), and the synthesis products were separated by dialysis. The results of optical measurements showed that the main source of luminescence of the obtained nanostructures are fluorescent particles or quasi-molecular fluorophores created in the ablation process. In the case of ablation in PEI, most of the produced molecular fluorophores are associated with carbogenic nanostructures, while in the case of EDA, free fluorescent molecules dominate.

Improved Laser Ablation Method for the Production of Luminescent Carbon Particles in Liquids

“…Therefore, as it can be seen, urea may enhance the optical properties of carbon nanoparticles to a degree comparable with more hazardous reagents as ethylenediamine (EDA) or polyethyleneimine (PEI). The lowest QY value of Sample B_W1 confirms the observation of the negligible fluorescent properties of CNPs produced by ablation of the graphite target in water [3,16]. Further irradiation of CNP suspension in water (Sample C_W1W2) results, however, in a significant increase in the QY value.…”

“…As it can be seen in Figure 2 a, the absorption spectra acquired from both synthesis stages (A_U1 and A_U1U2) display two absorption peaks, located at around 225 and 250 nm (the maximum of about 225 nm is distorted due to the high absorbance of the urea solution). These signals correspond to the π–π* transition of C–C bonds [ 1 , 2 , 3 , 4 , 5 , 6 , 8 ]. Although these spectra are similar, one can observe a distinctive increase in peak intensity after the second stage of Approach A accompanied by a decrease in the absorbance level at longer wavelengths.…”

“…Although the amount of reagents used in the PLAL approach in comparison to chemical methods is rather scarce (usually only one liquid medium is involved during the process), it is still difficult to exclude the effect of fluorophore molecules on the fluorescent properties of the suspension of carbon nanoparticles. On the one hand, CNPs produced by laser ablation in water are supposed to display negligible fluorescence, but on the other hand, CNPs obtained by laser synthesis performed in other liquids (such as acetone, isopropyl alcohol, polyethylene glycol, ethylenediamine, or polyethyleneimine) exhibit complex photoluminescence even after the use of separation methods such as dialysis [3,6,9,14].…”

“…The investigation of the mechanisms governing the photoluminescence of carbon nanoparticles (CNPs) has received substantial attention over the past decade [ 1 , 2 , 3 , 4 , 5 , 6 ]. In fact, it is perceived as a challenging task due to several fundamental ambiguities concerning not only the multitude of the production methods of a vast variety of different CNPs [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ] but also the lack of clarity in identifying the type of nanoparticles relevant [ 18 , 19 ].…”

“…Within the bubble, the pressure can reach several GPa, which enforces chemical interaction between vaporized medium and ablated species [ 20 ]. These conditions lead to the formation of many novel materials [ 3 , 6 , 7 , 8 , 9 , 10 , 11 , 13 , 14 , 15 , 16 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ].…”