Effect of (super)alkali doping on the electronic and second-order nonlinear optical properties of graphitic C3N4

A systematic analysis of electronic and nonlinear optical properties of a novel class of (super) alkali-doped complexes M/M3O@g-C3N4(M=Li, Na, K) is presented. These compounds exhibit considerable stability with large interaction energies, and M3O@g-C3N4 has higher stability than the corresponding M3O@g-C3N4. It is found that doping the (super)alkali can significantly narrow the wide energy gap of the pure g-C3N4 in the range of 2.04-2.84 eV, and these doped g-C3N4 show enhanced visible-light absorption. Due to the large charge transfer from (super)alkali to g-C3N4 moiety, these doped compounds exhibited significantly large first hyperpolarizabilities up to 2165-63761 au. The ratio between the vibrational and electronic contribution on hyperpolarizability indicates that the vibrational contributions play an important role in determining the static hyperpolarizabilities of certain systems. Therefore, (super)alkali-doped g-C3N4 are expected to be potential candidates for visible-light catalysis and high-performance nonlinear optical materials. We expect this work could provide a new idea for designing functional materials using superalkali clusters.