Journal of Alloys and Compounds 418 (2006) 35–38 Low voltage electroluminescence of terbium- and thulium-doped zinc oxide films S.A.M. Lima a , M.R. Davolos a,∗ , C. Legnani b , W.G. Quirino b , M. Cremona b a Unesp–Sao Paulo State University, Instituto de Qu´ ımica C.P. 355, 14801-970 Araraquara, SP, Brazil b Departamento de F´ ısica, PUC-Rio, Rua Marquˆ es de S ˜ ao Vicente, 225, 22453-900 Rio de Janeiro, RJ, Brazil Received 28 May 2005; received in revised form 31 August 2005; accepted 17 October 2005 Available online 18 January 2006 Abstract Strong interest in developing technology for visual information stimulates research for thin film electroluminescent devices. Here, for the first time, we report that thulium- and terbium-doped zinc oxide films are suitable for electroluminescence applications. Two different devices were assembled as ITO/LiF/ZnO:RE/LiF/Al or ITO/SiO 2 /ZnO:RE/SiO 2 /Al, where ZnO:RE is a film of zinc oxide containing 10 at% of Tb 3+ or Tm 3+ . Electroluminescence spectra show that besides a broad emission band with maximum around 650 nm assigned to ZnO, also emission lines from Tb 3+ at 484 nm ( 5 D 4 → 7 F 6 ), 543 nm ( 5 D 4 → 7 F 5 ), and 589 nm ( 5 D 4 → 7 F 4 ), or from Tm 3+ at 478 nm ( 1 G 4 → 3 H 6 ), and 511 nm ( 1 D 2 → 3 H 5 ) were detected. Intensity of emission as function of applied voltage and current–voltage characteristic are shown and discussed. © 2005 Elsevier B.V. All rights reserved. Keywords: Thin films; Semiconductors; Chemical synthesis; Electronical transport; Luminescence 1. Introduction The development of new optical displays for visual com- munication, such as flat panel displays (FPD), requires highly efficient devices. Electroluminescent (EL) displays, in particu- lar thin film electroluminescent display (TFEL), have been of scientific and industrial interest in recent years [1,2]. TFEL are complex optoelectronic multilayer devices that must combine electronic and optical properties of each layer to achieve the required characteristics. For example: high efficiency in con- verting electricity to light, high intensity of the emitted light, long lifetime of the device, and low voltage operation. A TFEL can be either inorganic or organic light emitting diode (OLED). The former is a heterojunction of a semiconductor and two insu- lator layers; in this case the optically active layer consists of a doped or undoped semiconductor from where light is emitted. Monochromaticity of the emitted light is highly desirable for applications in full color TFEL, and development of the blue light is still a challenge [1]. Rare earth (RE) ions have a favor- ∗ Corresponding author. Tel.: +55 1633016634; fax: +55 1633227932. E-mail address: davolos@iq.unesp.br (M.R. Davolos). able spectroscopy characteristic of emitting light in narrow lines, which makes compounds containing rare earths good candidates for optically active layer in full color or monochromatic displays. Thulium(III) is of particular interest among RE ions because it shows an interesting emission line in the blue region around 475 nm attributed to 1 G 4 → 3 H 6 transition [3,4]. Thulium-doped zinc sulfide has already been studied for TFEL application [5], although sulfide-based phosphors have some drawbacks such as a tendency to become saturated at high excitation density, and short lifetime of device due to decomposition [4]. Oth- erwise, zinc oxide is an extensively used material in a large variety of applications [4,6,7] due to its unique optical [6], elec- trical and structural characteristics [7], and stability [2]. EL of thulium-doped zinc oxide has been also reported, but just for a varistor type ceramic pellet [8]. Terbium(III) ions show green emission while terbium(IV) ions do not emit in the vis- ible range. Difficulties in the stabilization of the terbium(III) ion owe to its easy oxidation at high temperature and oxidizing atmosphere. The aim of this article is to report an easy method of prepa- ration for terbium(III)- and thulium(III)-containing zinc oxide films, and the electroluminescence of TFEL based on these two materials. 0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.10.066