Luminescence and magnetic properties of bifunctional nanoparticles composited by nitrogen-doped graphene quantum dots and gadolinium

Abstract

In this paper, nitrogen-doped graphene quantum dots (N-GQDs) were combined with gadolinium ions (Gd3+) by a surface modification to obtain magneto-optical dual-functional N-GQDs/Gd3+ nanoparticles. The morphology of obtained composite was characterized by field emission scanning electron microscopy and transmission electron microscopy. Luminescence and magnetic properties were measured by a fluorescence spectrophotometer and a vibrating sample magnetometer, respectively. Results indicate that well-dispersed spherical N-GQDs/Gd3+ nanoparticles have an average diameter of 7 nm. N-doping significantly increases the luminescence of particles with an optimal luminescence intensity at 20 °C and pH = 9. X-ray photoelectron spectroscopy results indicate that the N-doping introduces pyrrolic N as an electron donor, enhancing fluorescence by increasing the surface electron cloud density of N-GQDs. In addition, density functional theory calculation results reveal that N-doping reduces the band gap of N-GQDs/Gd3+, enabling electronic transitions to higher energy levels and generating more activation sites, thereby enhancing luminescence. Compared to N-GQDs/Gd3+ prepared at 20 °C, the saturated magnetization of particles prepared at 40 °C is 0.85 emu/g, indicating a better magnetic response. The above results suggest that bifunctional nanomaterials N-GQDs/Gd3+ with excellent optical properties and magnetism can be better used for fluorescence and magnetic resonance imaging.