Influence of bi-alkali metals doping over Al12N12 nanocage on stability and optoelectronic properties: A DFT investigation

Highlights: • Bi-alkali metal atoms doping over Al₁₂N₁₂ nanocage is investigated for the first time. • All doped Al₁₂N₁₂ nanocages exhibit significant thermodynamic stability upto -64.02 kcal/mol. • HOMO-LUMO gap in bi-alkali metal atoms doped Al₁₂N₁₂ nanocages is decreased upto 0.74 eV. • M₂@N_top and M₂@r₆ show monotonic increase in hyperpolarizability values with the size of alkali metal atoms. • Bi-alkali metal atoms doping brings remarkable increase in the NLO response of Al₁₂N₁₂ nanocages. Bi-alkali metal atoms (Li₂, Na₂, K₂) doped Al₁₂N₁₂ nanocages with remarkable stability are achieved for the first-time using density functional theory. Bi-alkali doping is a highly efficient technique to bring high stability as compared to single alkali metal atom doping. It is revealed that bi-alkali metal atoms doping significantly reduced the wide HOMO-LUMO energy gap (3.93 eV) of pure Al₁₂N₁₂ nanocage to 0.74–1.67 eV. The reduction in HOMO-LUMO energy gap is due to the formation of new HOMO energy levels having diffused excess electrons which is further confirmed by the PDOS and TDOS plots. The bi-alkali metal atoms doped Al₁₂N₁₂ nanocages exhibit remarkable nonlinear optical response. The highest first hyperpolarizability of 1.2 × 10⁵ au is observed for K₂@N_top. Clearly, the doping of high atomic number atoms brings larger hyperpolarizabilities, while the non-monotonic trend is observed for M₂@b₆₆ series where Na₂@b₆₆ has a large hyperpolarizability value. These fascinating results will be helpful for achieving the potential applications of inorganic Al₁₂N₁₂ nanocages in the optoelectronic devices and high performance nonlinear optical materials.