Linear and nonlinear optical absorption of 2D monolayer NbOCl2

The in-layer crystal structure of a two-dimensional material is stable, but the interaction force between the atomic layers is much weaker. Niobium oxide dichloride (NbOCl2) not only has high second-order nonlinear coefficients unique to common monolayer two-dimensional materials but also weak electronic coupling between layers. These characteristics make NbOCl2 very suitable as a quantum light source in quantum optical systems. This article mainly studies the linear and nonlinear optical absorption of two-dimensional monolayer NbOCl2. The characterization means include a surface distance projection map and three views, total density of states, photoelectron spectrum, charge density difference, transition dipole moment density, one-photon absorption spectrum, and two-photon absorption spectrum. There is a size effect on the total density of states, photoelec-tronic energy spectrum, and one-photon absorption spectrum, that is, as the size increases, the total density of states is red-shift, the photoelectronic energy spectrum is blue-shift, and the absorption spectrum has a signifi-cant red-shift. The charge density difference indicates that there is charge transfer around the Nb atom of NbOCl2. The transition dipole moment density changes periodically. The study of the two-photon absorption spectrum shows that it is dominated by a one-step transition. In summary, our work provides an in-depth un-derstanding of its optical properties and is of great significance for the miniaturization of quantum light sources.

Automated summary

This article investigates the optical properties of the two-dimensional material NbOCl2, which exhibits high second-order nonlinear coefficients and weak electronic coupling between layers, making it a suitable quantum light source material. The study reveals that the total density of states, photoelectronic energy spectrum, and absorption spectrum of NbOCl2 are influenced by the size effect. Charge transfer occurs around the Nb atom of NbOCl2 and the transition dipole moment density changes periodically. The two-photon absorption spectrum is dominated by a one-step transition.