Design of novel superalkali doped silicon carbide nanocages with giant nonlinear optical response

In this study, the electronic and nonlinear optical (NLO) properties of a novel class of superalkalis (Li₂F, Li₃O and Li₄N) doped silicon carbide (Si₁₂C₁₂) nanocages are investigated by using density functional theory (DFT) calculations. Computational results reveal that these complexes are quite stable and superalkalis prefer Si_top position of the nanocage energetically to be chemisorbed. The doping of superalkalis effectively reduced the HOMO–LUMO energy gap and transformed Si₁₂C₁₂ nanocage from insulator to n-type semiconductor. More interestingly, these complexes exhibited significantly large first hyperpolarizabilities (β_o) in the range of 2141–19864 au. This remarkable increase in first hyperpolarizability (β_o) values is due to small transition energies ΔE, which comes from the corresponding charge transfer from superalkali to the nanocage. The NLO response of the superalkali-doped Si₁₂C₁₂ nanocage was much better to those of their alkali-metal-doped analogs. Moreover, frequency dependent hyperpolarizability calculations are performed in the range of 400–1600 nm including 532 and 1064 nm for commonly used lasers. The TD-DFT analysis reveals that these complexes possess enough transparency in the UV region which is required besides large NLO response for practical applications in the field of opto-electronics. This study will provide new insights for designing of novel NLO materials having useful applications in all-optical switching, wavelength conversion and harmonic generation.