Graphene Controllable Luminescence Studies

This thesis explores the preparation techniques of graphene oxide using modified Hummers method.The graphene oxide obtained is characterized by XRD,TEM and Raman spectrum etc..Using graphene oxide as precursor,we prepared graphene quantum dots through hydrothermal method emitting at 435 nm.According to the AFM image of graphene quantum dots,the average size of graphene quantum dots are ranging from 15 nm to50nm.The height of dots are between 3nm and 5nm,which supports that our quantum dots are resulted from two dimensional structure of graphene oxide.Thus we report here a set of optimum parameters to synthesize GQDs by hydrothermal method,including hydrothermal temperature at 140?,hydrothermal time of 9 hours and dialysis time of 24 hours.Compared with the parameters reported by others,the photoluminescence intensity of our sample is 3 times higher.We also compared the photoluminescence intensity of our samples after 6 months under the same condition and it still illuminates the same intensity,which supports the reliability of our optimum parameters for stable high quality graphene quantum dots.Doping method is also adopted to regulate and control the peak position of graphene quantum dots.By condensation reacting in hydrothermal condition,the N/S-contained groups in cysteine will be bonding into the graphene quantum dots.The peak position of emission spectrum has been changed from 435 nm to 390 nm at the same excitation.A new kind of quantum dots reacted by cysteine itself has been discovered,which has the similar photoluminescence performance to graphene quantum dots.We can therefore control a set of regular changes of emission spectrum of graphene quantum dots from 390 nm to 435 nm by modulating the ratio of graphene oxide and cysteine.This has significant potential applications in future optoelectronic related fields.