The influence of substrate temperature on the structural and luminescent properties of as-deposited SrGa 2 S 4 :Ce 3+ th
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The influence of substrate temperature on the structural and luminescent properties of as-deposited SrGa2S4:Ce3+ thin films coated with a TaSi2 thin layer P. A. Moleme1 • H. C. Swart1
•
Vinod Kumar1 • J. J. Terblans1
Received: 2 October 2015 / Accepted: 12 February 2016 Springer-Verlag Berlin Heidelberg 2016
Abstract SrGa2S4:Ce3? thin films coated with a very thin layer of TaSi2 were deposited on Si(100) substrates utilizing the pulsed laser deposition system. During the ablation of the targets for thin films preparation, the Si(100) substrate temperature varied in the range of 400–600 C. The as-deposited SrGa2S4:Ce3? films showed an orthorhombic crystal structure, and the TaSi2 coating layer showed a hexagonal structure. The films maintained the crystal structures within the temperature ranges of 400–600 C. The distribution of particles with irregular sizes contributing to a difference in surface roughness of the as-prepared thin films was observed by atomic force microscopy. The films showed a broad photoluminescence (PL) peak at 416 nm, and the maximum PL intensity, as compared to other films, was observed for a film deposited at a substrate temperature of 450 C. Two broad cathodoluminescence peaks (440 and 490 nm) due to Ce3? emission were observed for a film deposited at a substrate temperature of 450 C. The presence of the TaSi2 coating layer on the SrGa2S4:Ce3? thin films was confirmed with Auger electron spectroscopy surface elemental analysis, and Auger depth profiles showed uniform concentrations of the main elements in the deposited films.
& H. C. Swart [email protected] & Vinod Kumar [email protected] 1
Department of Physics, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa
1 Introduction Cerium (Ce3?)-doped strontium thiogallate (SrGa2S4) is known to be a luminescent material having bright blue luminescence [1, 2]. When luminescent materials are exposed to an electron beam for a long period of time, electron-stimulated surface chemical reactions (ESSCRs) occur on the material surface [3, 4]. ESSCR result into a high degradation rate of the luminescence intensity and possible emission of gases which have undesirable effects, particularly when a luminescent material is used in field emission displays. As a result, the use of luminescent thin films with thin coating layers was considered to overcome these challenges, for this study in particular, the use of luminescent sulfide thin films. However, sulfide thin films exhibit only 40–75 % of the luminance brightness of the raw powder materials, due to factors such as grain structure, lack of stoichiometry transfer, type of substrate and film roughness [5]. In the case of thin coating layers, conductive oxides such as SiO2, CdO and SnO2 have been used to overcome the challenge of degassing in sulfidebased thin films [6–8]. Furthermore, the SrGa2S4:Ce3? luminescent material (phosphor) is well excited by photons, which are absorbed by the host-crystal atoms (SrGa2S4), and the energy transfer probably occurs between the
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