C8-structured carbon quantum dots: Synthesis, blue and green double luminescence, and origins of surface defects

Nanoscale carbon generally exists as nanodiamond or graphite quantum dot (QD). In this study, we report the first synthesis of the third allotrope carbon QDs with an average size of 2 nm through carbonization of sucrose and study their photoluminescence properties. These QDs have a body-centered cubic structure and each lattice point is composed of eight atoms which form a sub-cube (so called C8 crystal structure). High-resolution transmission electron microscopy and X-ray diffraction confirm the C8 structure of the synthesized nanocrystallites. The C8 QDs exhibit double-band luminescence with two peaks centered at around 432 and 520 nm. The study based on the photoluminescence, UV–Vis absorption, Fourier-transform infrared, and X-ray photoelectron spectroscopies reveals that the green emission originates from the CO related surface defect whereas the blue emission originates from another surface defect.