Applied Surface Science 258 (2012) 3255–3259 Contents lists available at SciVerse ScienceDirect Applied Surface Science j our nal ho me p age: www.elsevier.com/loc ate/apsusc Photoluminescence of undoped and Ce-doped SnO 2 thin films deposited by sol–gel-dip-coating method Shuai Chen ∗ , Xiaoru Zhao, Haiyan Xie, Jinming Liu, Libing Duan, Xiaojun Ba, Jianlin Zhao Key Laboratory of Space Applied Physics and Chemistry, Ministry of Education, School of Science, Northwestern Polytechnical University, Xi’an, 710072, PR China a r t i c l e i n f o Article history: Received 22 May 2011 Received in revised form 8 October 2011 Accepted 16 November 2011 Available online 25 November 2011 Keywords: Thin films Sol–gel Photoluminescence a b s t r a c t The undoped and Ce-doped SnO 2 thin films synthesized by a simple sol–gel-dip-coating method on glass substrates were investigated by means of X-ray diffractometer, visible spectrophotometer and photo- luminescence (PL) spectroscopy. The samples were polycrystalline thin films with rutile structure of undoped SnO 2 . A violet PL peak was observed in undoped SnO 2 at room temperatures, while a blue PL peak appeared only after introducing Ce 3+ ions into the SnO 2 host. The effects of Ce doping concen- tration and heat-treatment temperature on PL of the films were further studied, and the luminescence mechanism was also discussed. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Recently, rare earth elements doped semiconductor thin films have attracted extensive interest, due to their unique optical prop- erties and promising applications, such as fluorescent lamps and light emitting diode (LED) [1,2]. Semiconductor light-emitting materials could be generally divided into three classes, the sul- fur compound-based matrix [3], the oxide-based matrix [4] and nitride-based matrix [5]. Compared to traditional luminescent materials which based on sulfur compound, rare earth elements doped oxides possess obvious advantages, such as good chemical stability, high transparency in the range of visible light, and non- toxic. Especially, due to high concentration of oxygen vacancy on the surface, high electrical conductivity appears on the surface of oxide materials, preventing their surfaces from charge accumula- tion [6–10]. The approach of using rare earth element as activators and semiconductor thin films as host offers the advantages of com- bining the unique qualities of the semiconductor thin films and the optical properties of rare earth elements. Although most of the current studies on semiconductor lumi- nous oxides focus on ZnO [11–13], whose band-gap is 3.37 eV and exciton binding energy is 60 meV, another representative oxide SnO 2 has also caught increasing attention in luminous properties in recent years [14–16]. SnO 2 films show high transparency in the range of visible light and high conductivity [17]. Especially, com- pared to ZnO, SnO 2 has wider band gap of 3.6 eV and much higher ∗ Corresponding author. E-mail address: chenshuai19871219@163.com (S. Chen). exciton binding energy of 130 meV [18]. Therefore, the SnO 2 thin films have a widely application in blue emission devices. However, their PL properties were reported less than that of ZnO. With respect to the luminescence of SnO 2 thin films, the defects such as oxygen vacancies have been assumed to be the most likely recombination centers in the PL process. The light emission could be attributed to electron transition from the donor level formed by oxygen vacancy to the valence band in the film. In this work, Ce 3+ ion is chosen as the dopant in the study of luminescence of SnO 2 thin films. To our best knowledge, few investigations have been emphasized on this point up to now. The Ce 3+ ion has a very simple electron configu- ration, whose 4f–5d transitions are allowed and very sensitive to changes in the crystal field. The introducing of the Ce ions could induce new emissions to widen their application prospects. A variety of methods, such as chemical vapor deposition (CVD) [19], magnetron sputtering [20], pulsed laser deposition (PLD) [21] and sol–gel [22], are available to prepare SnO 2 films. Different fab- rication techniques greatly affect the performance of the films. The sol–gel method can precisely control the chemical composition of rare earth-doped SnO 2 films to obtain multi-component oxide films under simple technological equipment and low processing tem- perature [23–25]. In this work, we prepared the Ce-doped SnO 2 films using sol–gel dip-coating method. The effects of Ce doping and annealing on the structure and PL properties of the films, and the PL mechanism were also investigated and discussed. 2. Experimental The SnCl 2 sol was obtained by dissolving a given amount of ana- lytical grade SnCl 2 ·2H 2 O in 30 ml absolute ethanol. The solution 0169-4332/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2011.11.077