Phase formation of hexagonal wurtzite ZnO through decomposition of Zn(OH) 2 at various growth temperatures using CBD method Fokotsa V. Molefe a , Lehlohonolo F. Koao a,⇑ , Birhanu F. Dejene a , Hendrik C. Swart b a Department of Physics, University of the Free State (Qwaqwa Campus), Private Bag X13, Phuthaditjhaba 9866, South Africa b Department of Physics, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa article info Article history: Received 11 February 2015 Received in revised form 10 April 2015 Accepted 11 April 2015 Available online 18 May 2015 Keywords: ZnO CBD Temperature Nanophosphors abstract Zinc oxide (ZnO) nanophosphors were fabricated from zinc acetate dehydrate, thiourea and ammonia via the chemical bath deposition (CBD) method at various growth temperatures. TGA results showed the increase in thermal stability of ZnO with the increase in growth temperature. From DSC results we observed a decrease in melting temperatures due to the crystallization of the ZnO with the increase in growth temperature. The melting enthalpy values were too scattered to make definite conclusions. XRD indicated the decomposition of structure from Zn(OH) 2 to hexagonal wurtzite ZnO. The estimated average particle sizes are in the range of 22 nm. The estimated average particle size fluctuated with an increase in the growth temperature. The SEM morphology showed the full formation of flakes-like at high growth temperature. At low growth temperature shows flakes-like morphology combined with some small spheres. The EDS results confirmed the presence of Zinc (Zn) and Oxygen (O) as the major products, and the ratio of the Zn to O increased with the increase in growth temperature. A red-shift in reflectance spectra was observed, which resulted in the decrease in the band gap energy of the ZnO with an increase in growth temperature. The temperature dependent PL spectra of the ZnO showed visible emission due to defects. The novelty in this study lies within the increase in the amount of weight loss observed from TGA and DSC analysis and another important aspect is the transformation of Zn(OH) 2 to the well-known hexagonal wurtzite structure of ZnO with the increase in growth temperature. This study provides a simple and efficient approach for the synthesizing of the ZnO with flakes-like morphology. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction Most recently, the study on the luminescence behavior of the hexagonal wurtzite structure of ZnO has attracted vast attention owing to its unique structural, optical, thermal, electrical, and luminescence properties which can be exploited to manufacture promising phosphor materials [1–4]. Within various disciplines of nano-research, the control of structure and morphology has always been under extreme focus due to nanomaterial properties which are usually size, shape and distribution dependent [5]. The dependence of ZnO properties on the size and shape of the nanoparticles contributes toward various applications, such as ultraviolet (UV) photodiodes [6], spin light emitting diodes [7] and solar cells [8]. ZnO is the key inorganic material with novel applications in the field of nanoscience and nanotechnology. Furthermore the n-type semiconductor obtained many interesting applications because of its optical transparency in the visible region [9]. It is well known that ZnO has three stable structures, namely cubic rock-salt, zinc-blende and hexagonal wurtzite [10]. Among all metal oxide semiconductors ZnO is important both sci- entifically and industrially due to its wide band gap of 3.37 eV, and large exciton binding energy of 60 meV at room temperature (RT) [11,12]. Numerous synthetic methods such as sonochemistry [13], com- bustion method [14], sol–gel method [15], molecular epitaxial (ME) method [16] and hydrothermal process [17] have been used to prepare ZnO nanoparticles at high reaction temperatures. Some of these synthesis processes usually require long growth time, high temperature and poor quality control [18]. To circum- vent these challenges the chemical bath deposition (CBD) method was used to prepare ZnO at a low growth time and temperature. CBD is easy, cheap and user friendly since parameters such as pH, time, concentration and temperature can easily be varied http://dx.doi.org/10.1016/j.optmat.2015.04.034 0925-3467/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +27 58 718 5300; fax: +27 57185444. E-mail addresses: koaolf@qwa.ufs.ac.za, koao@webmail.co.za (L.F. Koao). Optical Materials 46 (2015) 292–298 Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat