Highly fluorescent green and red emissions from boron-doped graphene quantum dots under blue light illumination

Highly fluorescent boron-doped graphene quantum dots (B-doped GQDs, average particle size of ∼4 nm) are synthesized via one-pot solvothermal route in the presence of 1,3,6-trinitropyrene (TNP) and boric acid. The chemical ratio of the boric acid to TNP precursor is identified as a crucial factor in modulating the B-dopant concentration within the GQD lattices. The GQD suspensions maintain uniform dispersion over extended operation thanks to the NO₂ groups formed in the GQD edge sites promoting high dispersivity in polar and nonpolar solvents. The B-doped GQD suspensions are homogeneously stored in n-hexane and propylene glycol methyl ether acetate, enabling highly fluorescent green and red emission, respectively. Under the blue-light illumination, the green emission takes place at ca. 541 nm with a narrow full width at half maximum (FWHM) of 31.7 nm, whereas the red emission centers at ca. 617 nm with a FWHM of 42.5 nm. Through adjusting the concentration of B-dopant, the quantum yield of green and red fluorescence reached as high as 99.8 and 17.1%, respectively. Accordingly, the novel solvothermal synthesis route developed in this work provides the essential framework for engineering B-doped GQDs with tunable optical properties for high-performance biosensors and biomedical devices.