Optical Properties Of Doped Carbon Quantum Dots Based On Spectroelectrochemical Method

As a new class of zero-dimensional carbon nanomaterials,carbon quantum dots(CQDs)not only have the characteristics of low cost and easy fabrication,but also have excellent optical and electrical properties,which make them possess great application potential in the field of novel film optoelectronic devices,such as light-emitting diodes and solar cells,and have become a research hotspot in recent years.Generally,the photoluminescence of CQDs is closely related to the defect states and is easily affected by the external environment.To solve this problem,surface modification or the introduction of impurity atoms can be used to improve CQDs’ fluorescence quantum yield and photostability.However,the fluorescence of CQDs will be severely quenched induced by the formation of some new non-radiative channels when they are deposited into solid-state films from solution dispersion,which severely limits the application of CQDs in novel film optoelectronic devices.In this dissertation,we use the spectro-electrochemistry method to realize the fluorescence enhancement of a variety of doped CQD films and analyze the fluorescence enhancement mechanism in detail,which provides a solution to reduce the fluorescence quenching in carbon quantum dot solidstate films.The main research contents of this work are as follows:We investigate the relationship between the optical properties of nitrogen-doped CQDs(NCQDs)films and the electrochemical potential using spectro-electrochemistry methods.Applying a certain positive or negative potential resulted in fluorescence enhancement,with the positive potential having a greater enhancement(340% increment at +1.4 V)and the negative potential having a slightly weaker enhancement(10% increment at-1.4 V).It is confirmed by the absorption measurements that the dominant factor of the above fluorescence enhancement is not the change of samples’ absorption,but a large amount of charge injected when the electrochemical potential is applied,which weakens the non-radiative recombination process caused by the π-π stacking effect,thereby promoting the fluorescence enhancement of the N-CQDs film.By comparing with undoped CQDs,it can be confirmed that the large fluorescence enhancement exhibited by nitrogen-doped samples when applying positive potentials is related to nitrogen impurities.In addition,by guiding argon into the electrochemical cell,the accumulation of local charges can be reduced,and the low hysteresis reversible electrochemical regulation of the N-CQDs’ fluorescence can be realized.We investigate the effect of electrochemical potentials on the fluorescence properties of doubledoped(sulfur-nitrogen co-doped,fluoro-nitrogen co-doped)and single-doped(sulfur-doped)CQDs.Experimental results show that single-doped CQDs have more obvious fluorescence enhancement than double-doped CQDs under the same conditions.The fluorescence intensity of the sulfur-doped CQDs film is increased by 100% and 55.8% at the potential of + 2.0V and-2.0V,respectively.Similar to nitrogen-doped samples,experimental results show that the fluorescence enhancement of doped CQDs is not significantly related to the change of absorption intensity of the samples,but due to the weakening of intermolecular π-π interaction after a large amount of charge injection.The experimental results also prove that the turn-on potential of fluorescence enhancement is affected by doping elements,and the turn-on potential of single-doped CQDs is lower,which means that carriers are more easily injected into such samples.