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Variation of Optical Properties of Nitrogen-doped Graphene Quantum Dots with Short/Mid/Long-wave Ultraviolet for the Development of the UV Photodetector.

Nitrogen-doped graphene quantum dots (NGQDs) synthesized from a single glucosamine precursor are utilized to develop a novel UV-photodetector. Optical properties of NGQDs can be altered with short (254 nm), mid (302 nm) and longwave (365 nm) UV (ultra-violet) exposure leading to the reduction of absorption from deep to mid UV (200 to 320 nm) and enhancement above 320 nm. Significant quenching of blue and near-IR fluorescence accompanied by the dramatic increase of green/yellow emission of UV-treated NGQDs can be used as a potential UV-sensing mechanism. These emission changes are attributed to the reduction of functional groups detected by Fourier transformed infrared spectroscopy, and free radical-driven polymerization of the NGQDs increasing their average size from 4.70 to 11.20 nm at 60 min treatment. Due to strong UV absorption and sensitivity to UV irradiation, NGQDs developed in this work are utilized to fabricate UV photodetectors. Tested under long/mid/short-wave UV, these devices show high photo-responsivity (up to 0.59 A/W) and excellent photo-detectivity (up to 1.03X10^11 Jones) with highly characteristic wavelength-dependent reproducible response. This study suggests that the optical/structural properties of NGQDs can be controllably altered via different wavelength UV-treatment leading us to fabricate NGQD-based novel UV photodetectors providing high responsivity and detectivity.