Effect of an alkali hydroxide concentration on the structural, optical, and surface morphological properties of ZnO nano
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Effect of an alkali hydroxide concentration on the structural, optical, and surface morphological properties of ZnO nanoparticles S. Nilavazhagan1 · D. Anbuselvan1 · A. Santhanam1 · N. Chidhambaram1 Received: 23 January 2020 / Accepted: 10 March 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract A comprehensive study aimed to investigate the role of sodium hydroxide precursor concentration on the physical properties of the ZnO nanoparticles. A simple wet chemical approach was employed to synthesize ZnO nanoparticles by keeping the Zn precursor concentration constant and sodium hydroxide concentration varied. XRD analysis confirms the prepared ZnO nanoparticles having a hexagonal wurtzite phase whose crystallite sizes are from 24 to 34 nm. Good crystalline ZnO nanoparticles are realized when the Zn-to-OH precursor concentration is greater than 1:1 molar ratio. UV–Vis spectroscopic studies reveal the optical bandgap of the ZnO nanoparticles can be tailored considerably by varying the alkali hydroxide concentration. The variation in Urbach energy values emphasizes the existence of localized states originating from the lattice disorder and defects. The room temperature photoluminescence analysis confirms the presence of defects in the prepared nanoparticles. Surface morphological investigation of the synthesized nanoparticle samples was investigated using SEM. Keywords Metal oxide · ZnO · Internal parameter · Urbach tail · Intrinsic defects
1 Introduction In recent decades, metal oxide nanoscale materials have enticed much importance due to their multifarious applications, viz. light-emitting devices [1], solar cells [2], surface coatings [3], catalysis [4], water treatment [5], gas sensors [6], etc. Tailoring the structural, optical, and surface properties of these semiconductor materials provides a variety of applications as aforementioned. TiO2, SnO2, ZnO, ZrO2, CeO2, NiO, F e2O3, and I n2O3 are some of the commonly used semiconductors. Among these metal oxide semiconductors, ZnO is a versatile II–VI compound semiconductor having unique properties, viz. low-priced, innocuous, environmentally benign, thermally stable, and abundant material. It is also listed as a ‘Generally Recognized As Safe (GRAS)’ material by the US-FDA department [7]. As ZnO is an amphoteric oxide, it can readily react with acids as well as bases. Due to its wide bandgap of 3.37 eV, ZnO can be activated by ultraviolet radiation. On the other * N. Chidhambaram [email protected] 1
Department of Physics, Rajah Serfoji Government College (Autonomous) [Affiliated to Bharathidasan University], Thanjavur, Tamil Nadu 613 005, India
hand, the existence of defects and interstitials enables the ZnO as a visible light active semiconductor. The larger exciton binding energy (60 meV) of ZnO suggests its potential application as a UV emitting phosphor [8]. Further, nanosized ZnO particles are good antibacterial agents against pathogenic microorganisms [9]. Crystallite size and morphology take part in a crucial r
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