A nonlinear optical switch induced by an external electric field: inorganic alkaline-earth alkalide

Exploring a new type of nonlinear optical switch molecule with excess electron character is extremely important for promoting the application of excess electron compounds in the nonlinear optical (NLO) field. Here, we report external electric field (EEF) induced second-order NLO switch molecules of inorganic alkaline-earth alkalides, M(NH₃)₆Na₂ (M = Mg or Ca). The centrosymmetric structure of M(NH₃)₆Na₂ is destroyed in the presence of an EEF, and then a long-range charge transfer process occurs. It has been found that excess electrons are gradually transferred from one Na atom to the other Na atom through the inorganic metal cluster M(NH₃)₆. Finally, the excess electrons are completely located on one of the two Na atoms. In particular, the electronic contribution of the static first hyperpolarizability (β ^e ₀) for M(NH₃)₆Na₂ exhibits a large significant difference when the EEF is switched on. The β ^e ₀ value of M(NH₃)₆Na₂ is 0 when EEF = 0, while the peak β ^e ₀ values are 5.95 × 10⁶ (a.u.) for Mg(NH₃)₆Na₂ (EEF = 58 × 10^-4 (a.u.)) and 1.83 × 10⁷ (a.u.) for Ca(NH₃)₆Na₂ (EEF = 53 × 10^-4 (a.u.)). This work demonstrates that the compounds M(NH₃)₆Na₂ can serve as potential candidates for NLO switches.