Enhanced linear and nonlinear optical response of superhalogen (Al7) doped graphitic carbon nitride (g-C3N4)

Abstract

• Effect of Al 7 on g-C 3 N 4 is investigated for the second- and third-order NLO polarizabilities. • Doping reduces the band gap by about 50 % in the single doped system. Similarly, linear optical properties increase from 55 to 108 %. • The single doped system exhibited the first and second hyperpolarizability of about 39 and 5 times greater than the pure g-C 3 N 4 . In this study, pure and superhalogen doped g-C 3 N 4 clusters are computed with the CAM-B3LYP method of DFT to investigate the electronic and optical properties. Single Al 7 @g-C 3 N 4 and double doped 2Al 7 @g-C 3 N 4 systems are investigated. The doping of the superhalogen cluster on g-C 3 N 4 especially in a single doped system significantly improves the charge transfer properties by reducing the band gap energies from 6.42 eV to 3.23 eV. The average and total first hyperpolarizabilities ( β o and β total ) remarkably increase from 82 to 3204 au and 136–5340 au, whereas average second hyperpolarizability ( γ o ) increases from 14 × 10 4 to 64 × 10 4 au due to their lower transition energies. The selected systems were also compared with the external reference molecule p -NA which is a well-known reference molecule for NLO applications. TD-DFT simulations reveal that among pure, single, and double doped systems, the only single doped system shows significantly better outcomes including interaction energies, vertical ionization potential, HOMO-LUMO energies, and UV–vis absorption. The single doped system shows high absorption in the far-red region that use in lasers. The entitled systems especially single doped systems have the potential to use them as an efficient NLO material.