Optical absorption and photoluminescence of partially fluorinated graphite crystallites

Fluorinated graphene-like materials are currently attracting much attention due to the tuning of their properties by changing the fluorine content and pattern on the graphene lattice. In this work, we report the redshift of absorption bands and the suppression (increase) of green (yellow-orange) photoluminescence (PL) in the spectra of transparent CFx crystallites as x decreases from -0.44 to -0.33. Timedependent density functional theory (TDDFT) calculations reveal that the aromatic regions and polyene chains in the CFx layers are mainly responsible for the optical absorption of the samples in the ultraviolet and visible regions, respectively. The electron-hole recombination within branched aromatic rings or long carbon chains produces orange-red emission, while green-yellow PL is due to transitions of excited polyene electrons to half-occupied levels of aromatic carbon. Our results show that the optical properties of partially fluorinated graphite layers are determined by the size and shape of the remaining sp2 carbon regions, which can be varied by changing the fluorination conditions. (c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

Fluorinated graphene-like materials have attracted significant attention for their tunable properties via the manipulation of fluorine content and distribution on the graphene lattice. This study presents the redshift of absorption bands and the suppression (increase) of green (yellow-orange) photoluminescence (PL) in transparent CFx crystallites as the fluorine content x decreases from -0.44 to -0.33. Density functional theory (DFT) calculations show that the optical absorption in the ultraviolet and visible regions is attributed to the aromatic regions and polyene chains in CFx layers, respectively. The optical properties of partially fluorinated graphite layers depend on the size and shape of the remaining sp2 carbon regions, which can be controlled by altering the fluorination conditions.