It can be seen that the pristine adamantane is a consistent relative ultra-violet absorption wavelength as shown in table 3. Adding more Li and Na atoms, the absorption spectra shift toward to the left side which can be considered red-visible and near infrared in the absorption wavelength behavior. However, these spectrum still are in the near infrared wavelength behavior.
4. Summary
In summary, we have investigated the electronic and optical properties of the pristine and the functionalized adamantane molecules with substituting of Li and Na atoms by using time-dependent density functional theory (TD-DFT). We found that the electronic gap of adamantane significantly decreases under doping process with Li/Na atoms leading to semi-conductor behavior. The pristine adamantane has negative electron affinity but all structures of the modified adamantane have positive one. This feature characteristic of the pristine adamantane opens up to possibility of coating surface to produce electron emission devices. The calculated absorption spectra of the functionalized adamantane exhibit the red and the infrared shift suggesting to potential applications in optoelectronics device in these wavelength region.