Nonlinear optical properties of aluminum nitride nanotubes doped by excess electron: a first principle study

Aluminum nitride nanotubes (AlNNTs) doped by the excess electron, e@AlNNT and M@N-AlNNT (M = Li, Na, K), have been designed and their geometrical, electronic, and nonlinear optical (NLO) properties have been explored theoretically. The results showed that the excess electron narrows the energy gap between HOMO and LUMO values (E_H-L) of the doped systems in the range of 3.42-5.37 eV, which is due to a new energy level HOMO formed for the doped excess electron, with higher energy than the original HOMO of AlNNT. Importantly, the doped excess electron considerably increases the first hyperpolarizability (β₀) from 130 a.u. of the undoped AlNNT to 646 a.u. for e@AlNNT, 2606 a.u. for Li@N-AlNNT, while 1.14 × 10⁵ a.u. for Na@N-AlNNT, and 1.37 × 10⁶ a.u. for K@N-AlNNT. The enormous β₀ values for Na@N-AlNNT and K@N-AlNNT are attributed to the low transition energy. These results demonstrate that AlNNTs are a promising material in high-performance NLO nanomaterials for electronic devices.