The influence of oxygen vacancies on the optical and magnetic properties of Gd2O3/GQD nanocomposites

A one-step hydrothermal method was used to successfully synthesize the nanocomposites with an average size of 3.15 nm of graphene quantum dots (GQDs) and gadolinium oxide (Gd2O3), and a high-density ultrasonic vibration was applied to increase the concentration of oxygen vacancies in the obtained Gd2O3/GQD nanocomposites. The structure and properties of the nanocomposites were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and photoluminescence spectroscopy. It was found that after high-density ultrasonic dispersion for 2 h and 4 h, the fluorescence intensity of the nanocomposites was enhanced by about 42.7% and 54.6%, respectively, due to the formation of more activation sites induced by oxygen vacancies. The results of density functional theory (DFT) calculations confirmed the successful synthesis of the Gd2O3/GQD nanocomposites by Gd–O–C covalent bonds, and showed that the band gap narrowed (from 0.019 eV to 0.010 eV and 0.008 ev, respectively) for Gd2O3/GQD with more oxygen vacancies, offering an explanation to the enhancement of fluorescence intensity. Moreover, the magnetization increased (from 0.27 emu g−1 to 0.83 emu g−1) with the increasing concentration of oxygen vacancies. These results provide a favorable approach for realizing the application of the Gd2O3/GQD nanocomposites in the field of multimodal imaging.