Hindawi Publishing Corporation Journal of Spectroscopy Volume 2013, Article ID 424185, 5 pages http://dx.doi.org/10.1155/2013/424185 Research Article Structural and Optical Properties of ZnWO 4 :Er 3+ Crystals Nguyen Van Minh, 1 Nguyen Manh Hung, 1,2 Du Thi Xuan Thao, 2 Maarten Roeffaers, 3 and Johan Hofkens 4 1 Center for Nano Science and Technology and Department of Physics, Hanoi National University of Education, 136 Xuan Tuy Road, Hanoi, Vietnam 2 Hanoi University of Mining and Geology, Dong Ngac, Tu Liem, Hanoi, Vietnam 3 Centre for Surface Science and Catalysis, Katholieke Universiteit Leuven, Kasteelpark Arenberg 23, 3001 Leuven, Belgium 4 Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, 3001 Heverlee, Belgium Correspondence should be addressed to Nguyen Van Minh; minhnv@hnue.edu.vn Received 20 May 2013; Accepted 3 July 2013 Academic Editor: Pilar Leret Copyright © 2013 Nguyen Van Minh et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Erbium ion- (Er 3+ -) doped ZnWO 4 crystals were synthesized via a hydrothermal method with diferent erbium concentrations. Te prepared materials were characterized by X-ray difraction (XRD), scanning electron microscopy (SEM), and Raman, UV-Vis, and photoluminescence (PL) spectroscopy. For ZnWO 4 :Er 3+ crystals, a pure phase of ZnWO 4 was obtained without any evidence of impurity present. Te SEM images show that the grain size and morphology of ZnWO 4 :Er 3+ material depends on the Er 3+ -dopant concentration. Te UV-Vis spectra of ZnWO 4 :Er 3+ compounds exhibited an absorption band at about 323 nm (3.83 eV) stemming from the [WO 4 ] 2− . Other absorption bands centered at 367, 379, 408, 490, and 522nm are related to Er 3+ -ion transitions. Room temperature PL spectra of the ZnWO 4 :Er 3+ compounds exhibited visible emission at 515–540 and 545–565 nm corresponding to the 2 H 11/2 − 4 I 15/2 and 4 S 3/2 − 4 I 15/2 transitions of Er 3+ ions, respectively. 1. Introduction Rare-earth compounds have been widely used as phosphors in high-performance luminescent devices [1–3]. For such applications, rare-earth compounds have been introduced into a variety of host materials, and a lot of research efort has been focused on the development of novel and more facile synthesis procedures and on the tuning of the photoluminescence properties of rare-earth centers. ZnWO 4 is a very promising host material since it is nonhygroscopic and nontoxic, and it exhibits intrinsic photoluminescence properties. In the literature, various studies report on the doping of ZnWO 4 with a variety of rare-earth ions such as Eu [4, 5], Y [6], and Ho [7]. Doping other rare-earth element ions such as the Er 3+ ion has barely been investigated from a synthesis and photoluminescence point of view. On the other hand, the spectroscopy of the Er 3+ incorporated in a variety of other host materials has received much attention in the recent years, focusing especially on the development of green and infrared eye-safe laser [8]. Previously, Er 3+ -doped ZnWO 4 has been prepared via the Czochralski method [8]; however, this method requires high calcination temperatures. Reports on the hydrothermal synthesis of this material were not found. Furthermore, control of crystal morphology and size as well as the efects of surface area, crystallinity, and dispersion on the luminescent properties of Er 3+ -doped ZnWO 4 was not discussed in detail. In this work, we report on a facile hydrothermal synthesis procedure at low temperature (180 ∘ C) of Er 3+ -doped ZnWO 4 , and we discuss the efect of the composition on the structural and optical properties. 2. Experiments Erbium-doped zinc tungstate (ZnWO 4 ) nanoparticles were prepared by the hydrothermal reaction of Zn(NO 3 ) 2 ⋅6H 2 O,