Nonlinear optical properties of TeO$_2$ crystalline phases from first principles

TL;DR

This study uses first-principles calculations to analyze the nonlinear optical susceptibilities of two crystalline tellurium oxide phases, revealing significantly larger third-order susceptibilities than silica and linking structural features to optical properties.

Contribution

It provides the first computational analysis of nonlinear optical susceptibilities in crystalline TeO₂ phases, highlighting the role of structure and lone pairs in optical responses.

Findings

Third-order susceptibilities are two orders of magnitude larger than in α-SiO₂.

Electronic lone pairs of Te contribute significantly to large susceptibilities.

Structural features like helical chains influence anisotropy of susceptibilities.

Abstract

We have computed second and third nonlinear optical susceptibilities of two crystalline bulk tellurium oxide polymorphs: $\alpha$-TeO$_{2}$ (the most stable crystalline bulk phase) and $\gamma$-TeO$_{2}$ (the crystalline phase that ressembles the more to the glass phase. Third order nonlinear susceptibilities of the crystalline phases are two orders of magnitude larger than $\alpha$-SiO$_{2}$ cristoballite, thus extending the experimental observations on glasses to the case of crystalline compounds. While the electronic lone pairs of Te contribute to those large values, a full explanation of the anisotropy of the third order susceptibility tensor requires a detailed analysis of the structure, in particular the presence of helical chains, that seems to be linked to cooperative non-local polarizabilty effects. Our results demonstrate that first-principles simulations are a powerful predictive tool to estimate nonlinear optical susceptibilitites of materials.