Short Communication A new red colour emitting phosphor – ZnS:Mn co-doped with Ba for electroluminescent (EL) displays Panchatcharam Thiyagarajan a,b, * , M. Kottaisamy c , K. Sethupathi a , M.S.R. Rao a,b a Department of Physics, Indian Institute of Technology Madras (IITM), Chennai 600 036, India b Material Science Research Centre, Indian Institute of Technology Madras, Chennai 600 036, India c Department of Chemistry, Kalasalingam University, Krishnan Kovil, Sriveliputtur, TN, India article info Article history: Received 27 July 2008 Received in revised form 12 June 2009 Accepted 19 August 2009 Available online 22 August 2009 Keywords: Phosphor Luminescence X-ray diffraction abstract A new Mn activated Ba co-doped ZnS phosphor shows an interesting shift in the spectral emission from amber-yellow (570 nm) to red (620 nm) colour. To realize the phosphor material physics, attempts were made to fine tune the band gap of ZnS by co-doping Ba within the concentration range 2.50–10 mol%. Ba co-doping in ZnS host was achieved by sintering BaSO 4 with ZnS at 900 °C by carbothermal reduction method. Measurement of the CIE (Commission International deEchairge) chromaticity colour coordinates (x, y) of Zn 0.99 S:Mn 0.01 and Ba 0.10 Zn 0.89 S:Mn 0.01 phosphors shown to be (0.53, 0.47) and (0.65, 0.32), respectively. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Zinc sulfide (ZnS) is an important host material for the prepara- tion of phosphors (luminescent solids) for cathode ray tube and various display device applications. ZnS:Mn is an excellent thin film phosphor widely used in electroluminescence (EL) panels as an amber yellow colour emitting phosphor. It emits a broad band spectrum with a peak wavelength maximum at 582 nm due to 4 G( 4 T 1 )– 6 S( 6 A 1 ) transition. For a full colour EL display application, the amber light is filtered with red filters. This process tends to de- crease the intensity of emitted light. In order to avoid this problem, development of individual phosphors that emit at red and green wavelength regions is an essential step to realise full-colour-emis- sion of EL panels with high resolution. Based on the argument, by manipulating the defect manipulation in the solid and the subse- quent changes in the crystal properties in the desired host materi- als, essentially any colour can be represented over the entire portion of the visible spectrum viable for display device applica- tions. Indeed for the first time, we observed red emission from Ba co-doped ZnS:Mn system. The colour tuning of ZnS:Mn phos- phor emission wavelength has previously been accomplished by altering the band gap of materials. For example, a gradual increase of Mg concentration in Zn (1Àx) Mg x S:Mn leads to shorter emission wavelengths from amber to green. Therefore, emission colour is primarily determined by the magnitude of the band gap rather than the nature of dopant atom (Mn) [1,2]. In this work, we have synthesized the Mn activated Zn (1Àx) Ba x S phosphor by carbothermal reduction in conventional solid state method. The results of powder X-ray diffraction (XRD) and struc- tural aspects, photoluminescence (PL) and photoluminescence excitation (PLE) studies of Zn (1Àx) Ba x S phosphors are also discussed which could be useful for the fabrication of EL device. 2. Experimental details Samples of composition Zn (1Àx) Ba x S:Mn (0 < x < 10 mol%), with an increment in x by 2.5 mol%, were prepared by carbothermal reduction method through solid state reaction. To begin with, chemical ingredients consist of ZnS (Central Drug House – CDH, In- dia), BaSO 4 (CDH, India), and MnSO 4 ÁH 2 O were weighed in stoichi- ometric proportions along with excess sulfur and then mixed thoroughly in an agate mortar to form a homogeneous mixture. This step was crucial to maintain the stoichiometry of the phos- phor. The powder mixture was heated at 900 °C for 5 h in a reduc- ing carbon atmosphere in a muffle furnace. The structural aspects of the parent compound and final product was monitored by X-ray powder diffraction (XRD) using Cu K a radiation (k = 1.5405 Å). Pho- toluminescence (PL) and photoluminescence excitation (PLE) spec- tra were recorded at room temperature with a fluorolog spectrophotometer operating in the region of 325–800 nm using a 350 W xenon lamp. The CIE chromaticity coordinates of the phos- phors were measured using a USB2000 Ocean Optics spectrometer. 0141-9382/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.displa.2009.08.001 * Corresponding author. Address: Department of Physics, Indian Institute of Technology Madras (IITM), Chennai 600 036, India. E-mail addresses: thiyagu@physics.iitm.ac.in (P. Thiyagarajan), msrrao@iitm.ac. in (M.S.R. Rao). Displays 30 (2009) 202–204 Contents lists available at ScienceDirect Displays journal homepage: www.elsevier.com/locate/displa