Electrogenerated chemiluminescence from carbon dots
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Electrogenerated chemiluminescence from carbon dots L. Sun1,2, T.-H. Teng1, Md. H. Rashid1, M. Krysmann1, P. Dallas1, Y. Wang1, B.-R. Hyun2, A. C. Bartnik2, G. G. Malliaras1, F. W. Wise2, E. P. Giannelis1 1 Material Science and Engineering Department, 2School of Applied and Engineering Physics, Cornell University, Ithaca, NY14853, USA
ABSTRACT We report an interesting property of carbon dots: they emit light under charge injection. We synthesized carbon dots in diameter about 20 nm using wet chemistry methods. The photoluminescence quantum efficiency of the carbon dots dissolved in water was about 11%. We observed strong electrogenerated chemiluminescence (ECL) from the sample. This observation of ECL from carbon dots indicates that they could be a good candidate material for carbon-based electroluminescent devices. INTRODUCTION Fluorescent semiconductor quantum dots have generated broad promising applications including biological labeling and solid-state lighting. Nanometer-size carbon dots which are the counterparts of silicon nanoparticles now light up. Although the typical photoluminescence quantum efficiency of carbon dots is not high yet, they are non-blinking [1] and have large twophoton absorption cross section [2] which are favorable for one-photon or two-photon bioimaging. On the other hands, getting luminescence through charge injection has been tried by several groups [3], which is a step towards electroluminescence from carbon dots. Carbon dots could be a good candidate material for nontoxic carbon-based optoelectronic devices. There are two schools of fabrication methods for carbon dots: top-down, bottom-up. Topdown method starts from bulk carbon, and using laser [2] or electrochemical oxidation [4] to break down the carbon into small pieces which have the size in nanometer scale. Graphene fragment carbon dots exhibit size tunable optical properties [5]. The bottom-up method starts from organic molecules and using chemical reaction, pyrolysis method to fabricate carbon dots, pioneered by Giannelis groups [6]. Following this direction, we can make mass production of carbon dots. Above on this, we investigate their optical properties and observed bright electrogenerated-chemiluminescence (ECL) from carbon dots dispersed in acetonitrile solution. Moreover, ECL from carbon dot film sticking to the surface of mesoporous TiO2 is also observed. The spectrum of the ECL peaks at about 460 nm. The results indicate that the carbon dots we synthesized could be a good material for blue emitting LEDs. EXPERIMENT Carbon dot synthesis The method of synthesis of C dots is adopted from a previously reported method with some modification [6]. In a typical synthesis; a mixture of citric acid or acetylenedicarboxylic acid were mixed with ethanolamine under constant magnetic stirring to get a mole ratio of amine to acid of 3: 1 or 2: 1. After homogeneous mixing the reaction mixture was heated to above 70 °C to get a syrupy suspension which is pyrolyzed directly in a furnace at temperature more than 180 °C. The black produc
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