Optical properties of Janus and non-Janus diamanes monolayers using ab-initio calculations

•We study the properties of optical properties of Jnon-Janus C2Cl, C2F, C2H and Janus C4FCl, C4HCl, and C4HF diamanes.•These layers show a good absorption coefficient in the 3.00–35.00 eV region.•The reflectivity index spectrum confirms that the reflectivity is important in the visible-ultraviolet region up to 37.00 eV. The optical properties of solids are a major topic in both fundamental research and industrial applications. Understanding these properties has important implications both technologically and fundamentally. In this framework, we investigate the optical properties such as absorption, conductivity, refractive index, and dielectric function of non-Janus C2Cl, C2F, C2H and Janus C4FCl, C4HCl, and C4HF diamanes using the density functional theory. Our GGA calculations show that the imaginary part ε2(ω) of the dielectric function disappears at around 37.00 eV, which corresponds to the energy loss function gives a noticeable peak. This peak in energy loss function at about 37.00 eV awakes as ε1(ω) goes through zero and ε2(ω) is small at such energy, thus satisfying the condition for plasma resonance at 37.00 eV (here the compounds become transparent). For all GGA absorption calculations, we found that these layers show a good absorption coefficient in the ∼3.00–35.00 eV region. Moreover, we obtained the photoconductivity for each compound that begins with non-zero photon energy.