Multiple low-energy excitons and optical response of $d^0$ double perovskite Ba$_2$ScTaO$_6$

TL;DR

This study investigates the crystal structure, electronic properties, and optical response of the Ba$_2$ScTaO$_6$ double perovskite, revealing a large bandgap and multiple exciton modes extending into the visible spectrum.

Contribution

It provides the first detailed experimental and theoretical analysis of Ba$_2$ScTaO$_6$, highlighting its large bandgap and complex excitonic optical features, and compares different DFT approaches for accurate electronic property prediction.

Findings

Large bandgap of approximately 4.66 eV confirmed.

Presence of multiple exciton modes up to visible range.

Modified Becke-Johnson potential improves electronic gap estimation.

Abstract

Large bandgap insulators are considered promising for applications such as photocatalysts, dielectric resonators and interference filters. Based on synchrotron X-ray diffraction, diffuse reflectance measurement and density functional theory, we report the crystal structure, optical response, and electronic properties of the synthesized $d^0$ double perovskite Ba$_2$ScTaO$_6$. In contrast to earlier prediction, the electronic bandgap is found to be large, $\sim 4.66$ eV. The optical response is characterized by the presence of multiple exciton modes extending up to the visible range. A detailed investigation of the direct gap excitons based on the Elliot formula is presented. Density functional theory based investigation of the electronic properties within generalized gradient approximation severely underestimates the electronic gap. To reach a quantitative agreement, we consider different available flavors of the modified-Becke-Johnson exchange-correlation potential and discuss their effects on the electronic and optical properties.