Bi-doping of Alkali Metals M2 (M2=Li2, Na2, and K2) on Al12N12 Nano-cage: A New Effective Approach to Design Nonlinear Optical Materials

Abstract

Under the framework of density functional theory (DFT), M2@x-Al12N12 (M2=Li2, Na2, and K2; x=b66, Ntop, and r6) complexes have been designed. These highly stable complexes are formed through doping of bi-alkali metals at the surface of inorganic Al12N12 nano-cage. Both alkali metal atoms were doped in a trans-fashion over nitrogen atoms of Al12N12 (Ntop) or AlN fused bond (b66) and over six-membered rings (r6). For the b66 and Ntop positions, the trend of stability for the complexes is Li2->Na2->K2-complexes. However, in cage doping position of r6, the stability is increased in the order of Li2->K2->Na2-complexes. The analysis of our computed data revealed that the large band-gap between HOMO (Highest occupied molecular orbital) and LUMO (Lowest unoccupied molecular orbital) of pure Al12N12 nano-cage can be decreased significantly within the range of 0.74-1.67 eV through doping of bi-alkali metals, thus showing the fascinating n-type behavior. A new HOMO orbital formed between the original band-gap of pure Al12N12 is responsible for the reduction in band gap. The doping of bi-alkali metals M2 on Al12N12 nano-cage results in a remarkable nonlinear optical response (β0). The calculated highest first hyperpolarizability values are 127397.94 au for K2@NtopAl12N12, 670.67 au for K2@r6-Al12N12, and 1028 au for Na2@b66-Al12N12 respectively. The hyperpolarizability values are increased with the increase in the atomic number of bi-alkali metals when bi-alkali metals are doped over Ntop and r6 positions. These intriguing results would be helpful to pursue future uses of modified doped Al12N12-based nano-cages in the latest kind of electronic and high efficient NLO (Nonlinear optical) nano-devices.