Effects Of The Structures Of Carbon Quantum Dots On Luminescence Emission Behavior

Carbon quantum dots (CQDs) are dispersed and quasi-spherical nanoparticles with sizebelow 10 nm. They hold not only resembled luminescence emission behavior of traditionalsemiconductor quantum dots and up-converting optical property, but also easy to prepare andinexpensively. CQDs are used in bioinstrumentation, sensors, nonlinear optical,photoelectricity transformation and photocatalysis. With a number of significantbreakthroughs in synthetic routes, the luminescence mechanism of CQDs is not clear, whichseriously hindered the development of CQDs that are efficient and controllablephotoluminescence (PL) behavior. According to this, based on the experimental results andtheoretical calculation, the effects of the structures on the luminescence emission havior inCQDs will be studied in this article.Controling the laser parameters, CQDs with the fraction of sp~2-hybridized bonding werefabricated by laser irradiation graphite flakes and carbon black particles in ethanol suspension.At the same size distribution, the fraction of sp~2-hybridized in CQDs showed diverse PLbehavior. The spectral test results showed that the luminescent centers of CQDs increasedwith raising of the fraction of sp~2-hybridized. CQDs with oxygen content synthesized byrefluxing wood soot and the CQDs that were prepared by electrochenical etching graphite inethylene diamine tetraacetic acid disodium salt (EDTA-2Na) solution, respectively. Weanalyzed oxygen content dependent their PL behavior of CQDs and the results showed thatthe strongest PL peak of CQDs exhibted redshift with increasing of oxygen content. Moreover,CQDs of etching graphite in the electrolytic solutions affected PL behavior with differentoxygen content.On the basis of our experiment results, the conhesive energy was introduced into the firstprinciples method to built a bandgap theory model of CQDs structure. The model was used tocalculate CQDs bandgap of the different sp-hybrid orbital. The calculation results showed thatthe sp~2hybridized caused the defects and created a luminousent centers in CQDs. In a mixtureof sp~2and sp~3bonding, the bandgap could be controlable by the fraction of sp~2-hybridized.The theoretical results are consistent with the our experimental results.