Prediction of two-dimensional 2H-M2O3 (M = Ti and Zr) with strong linear and non-linear optical response in the infrared range†

Recently, MXene-like MOenes have emerged as promising candidates for next-generation two-dimensional optoelectronic devices due to their exceptional electrical and optical properties. By using first-principles calculations, we design a novel two-dimensional 2H-M₂O₃ (M = Ti, Zr) through the oxygen functionalization of the M₂O monolayer, which shows high mechanical, dynamic, and thermal stabilities. The calculation results reveal a relatively small band gap of 0.49 and 0.94 eV and exciton binding energy of 0.26 and 0.46 eV for 2H-Ti₂O₃ and 2H-Zr₂O₃ monolayers, respectively. Importantly, they exhibit good light absorption in the infrared range with a first excitonic peak at 0.31 and 0.54 eV, respectively. Notably, a wide transparent window from the visible to ultraviolet region in linear optical spectra is found due to the large gap within the valence bands. The octahedral distortion and small optical gap of the 2H-M₂O₃ monolayer result in a large second harmonic generation (SHG) coefficient of approximately 4000 pm V⁻¹. This work optimizes the electrical and optical properties of MOenes using O termination, providing high linear and SHG response at specific wavelengths.