Applied Surface Science 257 (2011) 10147–10155 Contents lists available at ScienceDirect Applied Surface Science j our nal ho me p age: www.elsevier.com/loc ate/apsusc Low voltage electron induced cathodoluminescence degradation and surface characterization of Sr 3 (PO 4 ) 2 :Tb phosphor I.M. Nagpure ∗ , Shreyas S. Pitale, E. Coetsee, O.M. Ntwaeaborwa, J.J. Terblans, H.C. Swart ∗∗ Department of Physics, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa a r t i c l e i n f o Article history: Received 22 April 2011 Received in revised form 3 July 2011 Accepted 4 July 2011 Available online 8 July 2011 Keywords: AES NanoSAM Photoluminescence Cathodoluminescence XPS ESSCR Electron degradation Sr3(PO4)2 a b s t r a c t Tb 3+ -doped Sr 3 (PO 4 ) 2 phosphor was prepared by a sol–gel combustion method. A trigonal structure hav- ing Sr and O atoms occupying two different lattice sites were obtained. Scanning Auger nanoprobe was used to analyze the morphology of the particles. Photoluminescence (PL) and cathodoluminescence (CL) properties of Sr 3 (PO 4 ) 2 :Tb powder phosphors were evaluated and compared. In addition, the CL intensity degradation of Sr 3 (PO 4 ) 2 :Tb was evaluated when the powders were irradiated with a beam of electrons in a vacuum chamber maintained at an O 2 pressure of 1 × 10 -6 Torr or a background pressure of 1 × 10 -8 Torr O 2 . The surface chemical composition of the degraded powders, analyzed by X-ray photoelectron spec- troscopy (XPS), suggests that new compounds (metal oxides) of strontium and phosphorous were formed on the surface. It is most likely that these compounds contributed to the CL intensity degradation of the Sr 3 (PO 4 ) 2 :Tb phosphors. The CL properties and possible mechanism by which the new metal oxides were formed on the surface due to a prolonged electron beam irradiation are discussed. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Phosphates are a very diverse class of compounds whose proper- ties cover all aspects of material science and physics [1,2]. They find applications in many fields of technical interest ranging from non- linear optics to lighting. The structures of phosphate compounds are rather complex with various sites available for occupation by divalent/trivalent cations. For example, in strontium-modified orthophosphates (Sr 3 (PO 4 ) 2 ) there are more sites from strontium that can be occupied by cations. As a result, Sr 3 (PO 4 ) 2 materials doped with cations (especially rare-earths) show a large variation in their luminescence behaviour [3]. Since rare-earths cations can occupy different sites in the lattice, they are usually used to probe the lattice structure [4]. Literature survey confirms that phosphate compounds are both chemically and thermally stable [5]. Because of this, they are widely used as host lattices for rare-earth ions to prepare phosphors that can be used in different types of light emitting devices. For example, it has been demonstrated that Tb 3+ doped Sr 3 (PO 4 ) 2 exhibits excellent luminescent properties when excited by UV light, cathode radiation or X rays [6–8]. Bril et al. [8] reported a bluish-white cathodoluminescence (CL), with long ∗ Corresponding author. ∗∗ Corresponding author. Tel.: +27 0 51 401 9749; fax: +27 0 51 401 3507. E-mail addresses: indrajitnagpure@yahoo.co.in (I.M. Nagpure), swarthc@ufs.ac.za (H.C. Swart). decay time, from microcrystalline Sr 3 (PO 4 ) 2 :Tb phosphor prepared by solid state diffusion. They evaluated this material for applica- tions in cathode ray tube of television and computer monitors. In recent years, the evaluation of CL properties of Sr 3 (PO 4 ) 2 :RE (RE = rare-earths) has been extended to possible application in low voltage field emission displays (FEDs) [9,10]. As mentioned above, two important reasons for studying phosphate based phosphors are their chemical and thermal stability, and variation in their emission colour which is influenced by the site occupied by light emitting cations. A correlation between the CL intensity radia- tion and the changes on the surface chemistry were studied. In addition, a possible mechanism of the CL intensity degradation is discussed. The CL intensity degradation of the Sr 3 (PO 4 ) 2 :Tb phos- phor was evaluated for a possible application of the phosphor in low voltage field emission displays. The sol–gel assisted combustion method was used to prepare Sr 3 (PO 4 ) 2 :Tb powder phosphor. X-ray diffraction (XRD), Scanning Auger nanoprobe (NanoSAM), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and CL spectroscopies were used to characterize the Sr 3 (PO 4 ) 2 :Tb 3+ powders. 2. Experimental 2.1. Phosphor synthesized Sr 3 (PO 4 ) 2 :Tb 3+ phosphors were prepared using the sol–gel assisted combustion method. All the chemicals used were of 0169-4332/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2011.07.008