Synthesis and comparative study of Ho and Y doped ZnO nanoparticles Shubra Singh ⁎, J.N. Divya Deepthi, B. Ramachandran, M.S. Ramachandra Rao Department of Physics, Materials Science Research Centre and Nano Functional Materials Technology Centre, Indian Institute of Technology (IIT) Madras, Chennai-600 036, India abstract article info Article history: Received 19 April 2011 Accepted 2 June 2011 Available online 13 June 2011 Keywords: Rare earth doping ZnO Microstructural Magnetic Particles Nanosize Sol–gel preparation Ho and Y doped ZnO nanoparticles were synthesized using a wet chemical route followed by structural, electrical and magnetic property characterization of the same. We present a comparison of the properties of Ho and Y (having same ionic radii) doped ZnO nanoparticles. X-ray diffraction studies of the diffraction data exhibit a monophasic wurtzite crystal structure similar to that of the parent compound, ZnO. Microstructural investigations of these samples by scanning electron microscopy show the presence of nanostructures. The optical measurements show an increase in the band gap of doped samples as compared to the undoped sample. DC magnetization measurements of Ho doped ZnO point towards the presence of hysteresis loop at 5 K with an H c of about 110 Oe for a nominal 1 mol% Ho doped sample. The resistivity of Ho doped sample is found to be higher as compared to the undoped and Y doped sample. © 2011 Elsevier B.V. All rights reserved. 1. Introduction ZnO based diluted magnetic semiconductors (DMSs) offer the possibility of probing magnetic phenomena in crystals with a simple band structure and excellent magneto-optical and transport proper- ties. Doping transition metal ions into ZnO as well as other wide band gap oxides and III–V semiconductors has been shown to propagate carrier-induced ferromagnetism [1,2]. It is notable that Coey et al. [3] proposed donor impurity band exchange in DMS oxides, showing that shallow donor electrons mediated ferromagnetic exchanges. Howev- er, there has been no unanimous agreement on the experimental results on transition-metal-doped ZnO. Recent results on Gd doped GaN, indicating high magnetic moments [4] have motivated us to investigate ZnO samples doped with rare earth (RE) metal ions. For the 3d transition metals, the 3d electrons are exterior and delocalized; leading to strong direct exchange interactions and high Curie temperatures, but often the orbital momentum is zero, leading to small total magnetic moments per atom. In the case of RE doping, the 4f electrons are localized; exchange interactions are indirect as they occur via the 5d or 6s conduction electrons. However the high orbital momentum leads to high total magnetic moment per atom. Glasses and crystals doped with rare-earth (RE) metal ions are still attractive as a possible active media for solid state lasers, operating in the visible, near-infrared (NIR) and infrared (IR) spectral region. RE doped ZnO also have potential applications as visible light emitting phosphors in high power lasers and other optoelectronic devices [5,6]. Detailed literature survey shows that there are not enough reports on the systematic studies of rare earth ions like Ho doping in ZnO. With this motivation, Ho was doped into ZnO matrix by sol–gel method and investigated to understand the optical, electrical and magnetic properties of the Ho ion doped samples. These properties have also been compared with Y doped ZnO nanoparticles (having nearly the same ionic radii as that of Ho), however, the difference being that Ho is magnetic (μ eff = 10.4 μ B ) and Y is nonmagnetic. 2. Experimental Doped ZnO nanoparticles were synthesized by sol–gel route (more information on synthesis given in supplementary information). The composition of the samples was determined by energy dispersive X-ray analysis. The phase purity and crystal structure of the samples were analyzed by PAN analytical Xpert-Pro-PHILIPS using Cu Kα 1 radiation (λ = 1.5405 Å). Sample characterization was carried out using high resolution scanning electron microscopy (HRSEM-PHILIPS, QUANTA-200), high resolution transmission electron microscopy (HRTEM), diffuse reflectance spectroscopy or DRS (Ocean optics USB 2000 spectrophotometer) respectively, Vibrating sample Magnetom- eter (VSM) and Impedance analyzer (Agilent 4294A, USA). 3. Results and discussion Powder X-ray diffractograms of the compounds (Supplementary Fig. 1), obtained using a Cu-K α radiation show single phase formation. In all these cases the data fitted well to the wurtzite and it is clear that these samples were of polycrystalline nature without any secondary phases. All the peaks in both Ho and Y-doped ZnO samples could be Materials Letters 65 (2011) 2930–2933 ⁎ Corresponding author. Tel.: +91 44 22575912. E-mail address: shubra6@gmail.com (S. Singh). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.06.006 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/matlet