Nonlinear Anisotropy in Phase-Tuned Wide-Gap Halides

TL;DR

This study explores the nonlinear optical properties of phase-controlled silver iodide thin films, revealing phase- and morphology-dependent anisotropic responses that are promising for quantum photonics.

Contribution

It demonstrates phase- and morphology-dependent nonlinear optical responses in AgI thin films, highlighting their potential for phase-selective nonlinear optics and quantum photonic applications.

Findings

Triangular gI (111) flakes show sixfold SHG symmetry.

Rod-shaped gI (101) samples display twofold symmetry in SHG and 2PPL.

AgI exhibits phase-dependent anisotropic nonlinear responses.

Abstract

Silver iodide (AgI) thin films offer a compelling platform for studying nonlinear optical phenomena due to their intrinsic noncentrosymmetric lattice and direct band gap. Here, we investigate the nonlinear optical properties of AgI thin films grown by physical vapor deposition that selectively produce zincblende (\zbAgI) and wurtzite (\wzAgI) phases. Using a combination of polarization-resolved second harmonic generation (SHG) and two-photon photoluminescence (2PPL) spectroscopy, we identify clear phase- and morphology-dependent anisotropic nonlinear responses. Triangular \zbAgI $(111)$ flakes exhibit sixfold SHG symmetry and isotropic 2PPL emission, while rod-shaped \wzAgI $(101)$ samples display twofold-symmetric patterns in both SHG and 2PPL, which are explained by polarization analysis using second- and third- order nonlinear susceptibilities. These findings establish AgI as a promising halide semiconductor platform for phase-selective nonlinear optics and quantum photonic applications.