Investigation of structural, morphological and optical characteristics of Mn substituted Al-doped ZnO NPs: A Urbach energy and Kramers-Kronig study

Present work deals with the investigation of structural, morphological, elemental, chemical bonding and optical properties of simple sol-gel synthesized Al-doped ZnO and Mn-substituted Al-doped ZnO nanoparticles (NPs) using XRD, FE-SEM, EDAX, FT-IR and DRS techniques, respectively. A comprehensive evaluation of optical properties has also been done by Kramers-Kronig (KK) relations. The structural studies have revealed that the obtained patterns are mainly assigned to the hexagonal wurzite structure of the reference. The morphological investigations confirm the constitution of homogenous nanoscale particles with average grain sizes less than 40 nm for both samples. The optical band gap of the prepared samples is calculated using DRS data in two ways, Kubelka-Munk relation, and KK method. The band gap results show a red-shift with Mn-substitution in Al-doped ZnO. The disorderness (Urbach energy) of the samples is observed to be decreased with an increase in both band gap energy and crystallite size. Moreover, the optical parameters of the prepared samples such as refractive index, extinction coefficient and also dielectric constants are evaluated by applying KK relations on reflectivity curves.