Investigation of phase segregation in yttrium doped zinc oxide

AbstractWe report the effect of phase segregation on the structural, morphological, and optical properties of sol–gel synthesized Zn 1 x Y x O samples indilute concentration of 1–5 %. X-ray diffraction patterns confirm that below 3% of Y doping, pure ZnO wurtzite structure phase is obtained andphase segregation of Y 2 O 3 appears at xZ0.03. XRD results are well supported by the results obtained from scanning electron microscopy,Photoluminescence and Raman spectroscopy techniques. The difference in the charge states, ionic radii and the coordination numbers of hostlattice and dopant ions leads to the phase segregation.& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: Crystal structure; Rare earth doping; Phase segregation; Raman spectroscopy 1. IntroductionZnO with a wide band gap (3.3 eV) and large exciton bindingenergy (60 meV) is the most studied material because of its widerange of applications in the field of optoelectronics devices [1–4].Although ZnO had been widely studied material for the pastdecades, the renewed interests are focused on the modi fications invarious physical properties by rare earth dopants. It has beenshown that doping rare-earth ions enable ZnO as a multifunctionalsystem. For instance, Ce doping results in the reduction of bandgap(redshift)[5] whereas Er doping enhances the band gap (blueshift) of the material [6]. Apart from band gap engineering,Anandan et al. [7] has reported the relatively high photonicefficiencies and improved photocatalytic activity for La dopedZnO samples. Further, the quenching of UV emission band andobservation of strong visible emission at 618 nm has beenreported for Eu doped ZnO [8]. Above studies indicate that thedesired modifications can be achieved by selecting suitable rare-earth dopants. However, in the context of realization of devices, itis important to understand the crystal structure and the optimiza-tion of the procedures as well as the extent of dopant up to whichit is soluble in the host matrix. There are many reports on thestructural and luminescence properties of rare earth doped ZnO[9,10] but there is hardly any report available on the effect ofphase segregation. Even though, Yttrium does not directly belongto rare earth group, it exhibits the p roperties similar to rare-earthions. It has been observed that there is an enhancement in defect-induced green–yellow visible emission which in turn is respon-sible for the enhanced magnetic performances in Y doped ZnOnanorods.Present work aims to determine the optimum solubility of Y inthe host ZnO and to understand the physical properties when Yions are doped in dilute concentration of 5%. The sol –gel route ischosen in the present study for the synthesis because of low cost,high yield, high purity and relatively easier process as comparedto other synthesis methods. Further, the effect of phase segrega-tion on the structural and optical properties of Y doped ZnOsamples are investigated by employing various techniques such as