Thickness-Dependent Photoluminescence Oscillations in Layered Violet Phosphorus

The robust excitonic effects in layered violet phosphorus (VP) render it an ideal platform for exploring photoluminescence (PL) at 2D nanoscale. However, limited research on its luminescent properties constrains understanding and hinders its potential future developments. Here, a detailed investigation into the thickness-dependent PL evolution in multilayer VP samples is conducted, where their thicknesses are precisely controlled through the oxygen plasma dry etching technique. The pronounced exciton-trion interaction determines the envelop of the PL spectra. And as etching time increases, leading to decreased sample's thickness, the spectra peak blue-shifts, and the exciton-trionic ratio changes. However, an unusual spectral oscillation in a small number (≈12%) of VP samples is discovered, despite the majority exhibiting the typical overall decaying tendency with decreasing thicknesses. Subsequent characterizations, especially through the cross-sectional high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images and the measurements of second harmonic generation (SHG), hint at the possible existence of an allotrope new-phase VP. First-principles calculations, in conjunction with energy band theory analysis, are employed to delve into and elucidate the spectral alterations resulting from carriers non-radiative/radiative recombination in the different materials. This work lays a foundation for understanding the luminescent properties of layered VPs.