Endohedral metallofullerene electrides of Ca12O12 with remarkable nonlinear optical response

Herein, the structural, electronic, thermodynamic, linear and nonlinear optical properties of inorganic electrides, generated by alkali metal doping in group II-VI Ca12O12 fullerene, are studied. Endohedral doping of alkali metal leads to the formation of electrides whereas no such phenomenon is seen for exohedral doping. The electride nature of the endohedral fullerenes is confirmed through the analysis of frontier molecular orbitals. The results show that doping of alkali metal atoms leads to a reduction of the HOMO-LUMO gap and increase of the dipole moment, polarizability and hyperpolarizability of nanocages. Doping causes shifting of electrons from alkali metal atoms towards the Ca12O12 nanocage, which serve as excess electrons. Furthermore, the participation of excess electrons for enhancing the NLO response of these nanocages has been confirmed through the calculation of hyperpolarizability (beta(o)). For exploring the controlling factors of hyperpolarizability, a two level model has been employed and the direct relation of hyperpolarizability with Delta mu & f(o), while an inverse relation of hyperpolarizability with Delta E has been studied. The electrides possess remarkable nonlinear response where the highest hyperpolarizability can reach up to 1.0 x 10(6) a.u. for endo-K@Ca12O12. This electride has the lowest Delta E of 0.63 eV among all compounds studied here. These intriguing results will be expedient for promoting the potential applications of the Ca12O12-based nano systems in high-performance nonlinear optical (NLO) materials.

Automated summary

This study investigates the properties of inorganic electrides generated by alkali metal doping in Ca12O12 fullerene, confirming the electride nature through analysis of frontier molecular orbitals. Doping of alkali metal atoms results in reduced HOMO-LUMO gap, increased dipole moment, polarizability, and hyperpolarizability of nanocages. The shifting of electrons from alkali metal atoms to the Ca12O12 nanocage enhances the nonlinear optical response, with the highest hyperpolarizability reaching 1.0 x 10(6) a.u. for endo-K@Ca12O12.