Nanoparticle Size Effect Investigation of Nitrogen-doped Carbon Quantum Dots with their Fluorescence Properties

In this study, the nitrogen-doped carbon quantum dots were synthesized via microwave method using citric acid and urea precursors in a homogeneous aqueous solution. A centrifuge machine was used to eliminate large particles from the samples and to sort nanosized particles with variable centrifugal forces. X-ray diffraction pattern was obtained in order to study the formation of crystalline structure type of the sample and the size of crystallite. The broadening of peak indicated the nanosized formation of synthesized particles. Optical properties of the samples were examined by ultraviolet-visible and photoluminescence spectrometers. The absorption peaks wavelengths depended on particle sizes and had blue shift by decreasing of particle sizes. The Tauc plot indicated that energy gap increased from 2.39 eV to 2.62 eV with decreasing particle size. Emission peaks of nitrogen-doped carbon quantum dots, under the excitation of ultraviolet light, had fluorescence radiations in the visible spectral region of the green-blue.