Applied Surface Science 264 (2013) 237–241 Contents lists available at SciVerse ScienceDirect Applied Surface Science j our nal ho me p age: www.elsevier.com/loc ate/apsusc X-ray absorption spectroscopy and photoluminescence study of rare earth ions doped strontium sulphide phosphors Ankush Vij a,b,∗ , Sanjeev Gautam a , Vinay Kumar c , R. Brajpuriya d , Ravi Kumar b , Nafa Singh e , Keun Hwa Chae a,∗ a Advanced Analysis Centre, Korea Institute of Science and Technology, Seoul 136791, Republic of Korea b Centre for Material Science and Engineering, National Institute of Science and Technology, Hamirpur 177005, India c School of Physics, Shri Mata Vaishno Devi University, Katra 182320, India d Amity School of Engineering and Technology, Amity University Haryana, Gurgaon 122413, India e Department of Physics, Kurukshetra University Kurukshetra, Kurukshetra 136119, India a r t i c l e i n f o Article history: Received 25 March 2012 Received in revised form 26 September 2012 Accepted 2 October 2012 Available online 17 October 2012 Keywords: NEXAFS SrS:Sm PL emission and excitation a b s t r a c t We present here the electronic structure and photoluminescence properties of Sm (0.1–1.0 mol%) doped SrS phosphors. The doping in SrS was probed by near-edge X-ray absorption fine structure (NEXAFS) at M 5,4 -edges of Sm in total electron yield mode. The simulated absorption edges using atomic multiplet calculations were correlated with experimental results, which clearly reveal the presence of trivalent state of Sm in SrS matrix. However, for Sm (1 mol%), very minor traces of Sm 2+ were also observed, which have been explained by comparing the NEXAFS spectra in total electron and florescence yield mode. The PL emission of SrS:Sm comprises of three sharp bands at 567, 602 and 650 nm owing to the well- known intra 4f transitions from 4 G 5/2 to 6 H J (J = 5/2, 7/2, 9/2) levels of Sm 3+ ions in SrS host. The effect of Ce co-doping on SrS:Sm phosphors was also investigated, which exhibits characteristic PL emission of independent ions at their respective excitation wavelengths. However, at an excitation wavelength of 393 nm, SrS:Ce,Sm exhibits the simultaneous characteristic PL emission of both ions spanning into blue–green–red region. The CIE chromaticity coordinates also clearly show the influence of excitation wavelengths on the emission colour of SrS:Ce,Sm. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Generally, the alkaline earth sulphides (AES) in their pure form are indirect wide band gap semiconductors, which act as lumines- cent materials or phosphors after doping with suitable impurities. The AES phosphors find enormous applications in IR sensors, X- ray radiation imaging plates, optical storage media, bio-medical applications, radiation dosimetry, ionoluminescence, electrolumi- nescent devices, light emitting diodes, etc. [1–6]. The rare earth ion doped AES have received a great attention in the phosphor display industry due to its high luminous effi- ciency. SrS, a member of AES, with a band gap of 4.2 eV, can be tuned to different emission colours by the proper choice of dopant. The photoluminescence (PL) of rare earth ions activated phos- phors strongly depends on their valence state in the host matrix, therefore it is important to probe the valance state of dopant. We used element specific near-edge X-ray absorption fine structure (NEXAFS) technique to probe the presence and electronic structure ∗ Corresponding authors. E-mail addresses: vij anx@yahoo.com (A. Vij), khchae@kist.re.kr (K.H. Chae). of dopant in SrS. The fundamental phenomenon underlying NEX- AFS is the absorption of an X-ray photon by a core level of an atom in a solid and the consequent emission of a photoelectron. It is based on the determination of the X-ray absorption coefficient depending on the photon energy at a fixed angle of illumination. As the optical excitation of a core level electron requires the bind- ing energy as minimum photon energy, the transgression of this energy will coincide with an increased absorption coefficient. This leads to the formation of absorption edges, which may be indexed by their atomic subshell. In the present paper, we choose to investigate the role of Sm (0.1–1.0 mol%) as a dopant in SrS host. The Sm, predominantly found in 3+ charge state in AES, exhibits line PL spectra in the low energy side of visible spectrum, which are governed by intra 4f transitions [7,8]. It is known that AES phosphors are potential can- didates for emitting white light radiations which can be obtained by the combination of two or more phosphor materials or a sin- gle phosphor with a broad PL emission spectrum [9,10]. Since, Ce also predominantly exists in 3+ charge state in SrS, exhibits a broad PL spectra in the blue–green region of visible spectrum, which are governed by 5d–4f transitions [11,12], it is worthwhile to investi- gate the effect of Ce co-coping on the PL of SrS:Sm phosphor for 0169-4332/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2012.10.007