Accuracy in Estimating the Absorption Coefficient of Powder Nanomaterials: Resolving Misconceptions in Tauc Plot Application for Energy Bandgap Determination

Abstract

The accurate estimation of optical absorption coefficient ([[EQUATION]]) for powder nanomaterials for use in Tauc plot analysis remains a challenge due to the lack of explicit methodologies in the literature. This ambiguity leads to inconsistencies in bandgap determination and improper labeling of units on Tauc plot axes, particularly for nanopowder samples without measurable thickness. This study provides a detailed methodology for estimating α for nanopowders using UV-vis-NIR spectroscopy data, and proposes alternative graphing techniques that circumvent the need for thickness measurements. The results demonstrate that, while the conventional Tauc plot ([[EQUATION]]hν)n vs. hν can yield accurate bandgap values regardless of thickness substitution, the unit of ([[EQUATION]]hν)n must reflect whether path length was included in α calculation. Furthermore, alternative methods (modified Tauc plots) such as (Ahν)n vs. hν, and An vs. hν, which do not require thickness measurements, were validated as reliable methods for bandgap estimation. Practical demonstrations using SrZrO3, TiO2:Li,Co nanopowders, and ZnO thin film confirmed the robustness of these methods and ensured consistency with literature values. It is hoped that the present work would assist to curtail the widespread of unwarranted units on the Tauc plot. The correct unit should be written based on how the Tauc’s equation was manipulation.

Keywords: Absorption coefficient, Tauc plot, Energy bandgap, Semiconductors, UV-vis-NIR spectroscopy