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

Agata Kaczmarek,Jacek Hoffman,Zygmunt Szymański,Tomasz Mościcki,Artur Małolepszy,Jerzy Morgiel,Leszek Stobiński

doi:10.3390/ma14040729

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.

Highlights

Most of carbon dots (CDs) were synthetized in a chemical way, usually by hydrothermal carbonization of citric acid (CA) functionalized with various organic, usually amine-terminated compounds like ethylenediamine (EDA) [3,4,5], branched polyethylenimine (BPEI) [6], and L- cysteine [7], because the synthesis resulted in nitrogen-doped CDs with high photoluminescence quantum yield (PLQY) [3,4,5,6,7,8,9]
Optical measurements confirm that fluorescent molecules or quasi-molecular fluorophores are produced by laser ablation of the carbon target in PEI and EDA, albeit in relatively small amounts, with many more molecules being produced in EDA
Molecular or quasi-molecular fluorophores dominate in PLE scans but have rather little effect on the absorption spectra, at least in the case where the fluorescent molecules are not very numerous

Summary

Introduction

Most of CDs were synthetized in a chemical way, usually by hydrothermal carbonization of citric acid (CA) functionalized with various organic, usually amine-terminated compounds like ethylenediamine (EDA) [3,4,5], branched polyethylenimine (BPEI) [6], and L- cysteine [7], because the synthesis resulted in nitrogen-doped CDs with high photoluminescence quantum yield (PLQY) [3,4,5,6,7,8,9]. The origin of the photoluminescence spectra of carbon nanodots is a very important issue and has been studied in several papers from the last decade [3,4,5,6,7,8,9,10,11,12,13,14,15]. Most of papers assigned the absorption peaks in the ultra-violet (UV) region below 280 nm to π-π*

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