Layered NbOCl2 kinetic degradation mechanism and improved second-order nonlinear optical responses†

Abstract

NbOCl₂ exhibits exceptional nonlinear optical response, particularly for second harmonic generation (SHG). However, the environmental degradation mechanism of NbOCl₂ remains incompletely understood, posing challenges to device stability and optimization. This work demonstrates the kinetic degradation mechanism of 2D layered NbOCl₂ and proposes a strategy to improve the stability of nano-sized materials. It is primarily driven by the preferential replacement of Cl⁻ ions in NbOCl₂ with OH⁻ ions, which is regulated by storage temperature and H⁺ ions in the solution. Notably, the SHG response can be tuned effectively by altering the excitation power, degradation time, and irradiation wavelength. Additionally, the significant SHG of the NbOCl₂ nanosheets is remarkably stable when protected by poly methyl methacrylate. These findings offer novel insights into kinetic degradation mechanisms and strategies to improve the stability of NbOCl₂.