Structural and Optical Properties of ZnWO4:Er3+ Crystals

Erbium ion- (Er3+-) doped ZnWO4 crystals were synthesized via a hydrothermal method with different erbium concentrations. The prepared materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman, UV-Vis, and photoluminescence (PL) spectroscopy. For ZnWO4:Er3+ crystals, a pure phase of ZnWO4 was obtained without any evidence of impurity present. The SEM images show that the grain size and morphology of ZnWO4:Er3+ material depends on the Er3+-dopant concentration. The UV-Vis spectra of ZnWO4:Er3+ compounds exhibited an absorption band at about 323？nm (3.83？eV) stemming from the [WO4]2？. Other absorption bands centered at 367, 379, 408, 490, and 522？nm are related to Er3+-ion transitions. Room temperature PL spectra of the ZnWO4:Er3+ compounds exhibited visible emission at 515–540 and 545–565 nm corresponding to the 2H11/2？4I15/2 and 4S3/2？4I15/2 transitions of Er3+ 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 effort 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. ZnWO4 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 ZnWO4 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 Er3+ ion has barely been investigated from a synthesis and photoluminescence point of view. On the other hand, the spectroscopy of the Er3+ 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, Er3+-doped ZnWO4 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 effects of surface area, crystallinity, and dispersion on the luminescent properties of Er3+-doped ZnWO4 was not discussed in detail. In this work, we report on a facile hydrothermal synthesis procedure at low temperature (180°C) of Er3+-doped ZnWO4, and we discuss the effect of the composition on the structural and optical