Copper-doped Al12N12 nano-cages: potential candidates for nonlinear optical materials

DFT calculations have been performed to study geometric, electronic and NLO properties of copper-doped Al12N12 nano-cages. Doping of copper significantly reduces HOMO–LUMO gap of the nano-cages. The most prominent change in E g is observed for Cu@R6 (copper at the center of the six-membered ring), where E g is reduced by 52% of the original value. Total and partial densities of states have been plotted for all the structures revealing that a new HOMO has appeared between the original frontier molecular orbitals of Al12N12. Polarizabilities and hyperpolarizabilities show manifold increase (α = 418 au and β 0 = 1.8 × 104 au for Cu@R6) than pure Al12N12. TD-DFT calculations have been performed to obtain crucial excited states to account for the high hyperpolarizability values. The hyperpolarizability trend estimated from the two-level method and DFT calculations correlates nicely. The hyperpolarizability trend is justified nicely from the decreased E g. These findings designate such doped nano-cages as excellent candidates for their potential applications in electronic devices.