Study On Luminescence Properties Of Graphene Oxide Thin Films

Graphene oxide(GO),as a new pattern of carbon nanostructured material,has good hydrophilicity due to a large number of oxygen-containing functional groups on its surface,which is easy to realize material composite and large-area film-forming,which greatly expands the application of graphene based materials in the fields of biology,medicine,chemistry,materials and so on.In particular,oxygen-containing groups divide the ? conjugated system in the graphite sheet into carbon nano clusters with different sizes.Due to the quantum confinement effect,carbon nano clusters show semiconductor characteristics and luminescence characteristics,which is expected to expand the application of GO based materials in the field of Optics and biological monitoring.However,the luminescence intensity of GO film is weak,which greatly limits its application in the field of optics.At present,the luminescence mechanism of GO and the factors affecting the luminescence intensity of GO have not been clearly understood.Carrying out relevant research is of great significance to improve the luminescence intensity of GO films and regulate the luminescence characteristics of GO films.In this paper,the dependence of the luminescence of GO films on their layer spacing is studied;The luminescence mechanism of GO films and the factors affecting the luminescence intensity of GO films were systematically studied.The specific research contents are as follows:1.The effect of layer spacing on the luminescence intensity of GO films was studied,and the related luminescence mechanisms were discussed.The layer spacing of GO is controlled by water absorption / dehydration process.The results show that the layer spacing is obviously dependent on the luminous intensity.In the process of water absorption,the layer spacing of GO increases and the luminous intensity of GO increases;In the process of water loss,the layer spacing of GO decreases and its luminous intensity decreases.In particular,abnormal phenomena are found in the process of water loss.Compared with the case of no water filling between GO layers,the layer spacing of GO is smaller and the luminous intensity is weakened in the case of limited single-layer water.This is because the van der Waals force between water clusters and lamellae is closer to the layer spacing of GO(reduced by 0.02 (?))in the case of limited single-layer water between GO layers.The results show that the layer spacing of GO decreases and its luminous intensity decreases in the range of 0-3 GPa,which further proves the dependence of luminous intensity on the layer spacing of GO.The results of Raman spectroscopy showed that sp2 C / sp3 C did not change significantly in the range of 0-3 GPa,indicating that there was no structural phase transition in GO,and the structure of alternating distribution of sp2 C and sp3 C in the lamella did not change.It proved that the change of GO luminescence intensity did not come from the interaction between sp2 C carbon clusters in the same lamella,but from the interaction between sp2 C carbon clusters in different lamellae.Due to the decrease of GO layer spacing,the wave functions of sp2 carbon clusters between layers overlap,which accelerates the recombination of non radiative transition channels between electrons and holes,and then fluorescence quenching occurs,which is similar to the fluorescence quenching phenomenon during the aggregation of carbon quantum dots.This provides an important experimental basis for further understanding the luminescence mechanism of GO.2.The variable temperature luminescence of GO at different excitation wavelengths was studied.The results show that the luminescence intensity of GO does not change significantly in the temperature range of 80 k-220 k under 514 nm excitation;Under 830 nm excitation,the luminescence intensity of GO does not change significantly in the temperature range of 80 k-160 k.This result can be explained by the energy band structure of GO.sp2 carbon clusters are surrounded by high barrier sp3 carbon clusters.sp2 carbon clusters are subject to strong confinement effect,which increases the probability of electron holes on radiation transition,so the luminescence is less affected by temperature.In addition,the thermal activation energy under 514 nm excitation is 56 Me V higher than that under 830 nm excitation.This is because the size of sp2 carbon clusters under 514 nm excitation is smaller,the stronger the confinement effect is,the less the luminescence is affected by temperature.