Luminescence efficiencies of self- and Tm 3 þ activated CaWO 4 under vacuum ultraviolet radiation excitation Seon-Bae Kim a , Byung Gon Kum a , Hyun Myung Jang a , Arunachalam Lakshmanan b,n , Bong koo Kang c a Department of Materials Science and Engineering, Pohang University of Science and Technology, San 31, Hyoja-Dong, Pohang, Kyungpook 790-784, South Korea b Saveetha Engineering College, Thandalam, Chennai 602105, India c Department of Electronic and Electrical Engineering, Pohang University of Science and Technology, San 31, Hyoja-Dong, Pohang, Kyungpook 790-784, South Korea article info Article history: Received 31 October 2005 Received in revised form 11 October 2010 Accepted 29 March 2011 Available online 9 April 2011 Keywords: VUV fluorescence Color purity Grain size Self- and Tm activated CaWO 4 BAM:Eu 2 þ Blue PDP phosphor abstract Luminescence efficiency of self-activated CaWO 4 under 147 nm vacuum ultraviolet (VUV) radiation excitation is about 90% of that of BaMgAl 10 O 17 :Eu 2 þ (BAM), the commercial blue plasma display panel (PDP) phosphor. However, the color purity and the particle size of the former needs substantial modification before it can be considered for application in PDP. CaWO 4 :Tm exhibits Tm 3 þ emission peaks in the blue region due to energy transfer from WO 4 to Tm 3 þ ions but the overall emission intensity under 147 nm excitation is reduced when compared to that of CaWO 4 . & 2011 Elsevier B.V. All rights reserved. 1. Introduction The most vulnerable plasma display panel (PDP) phosphor under the harsh conditions of a Ne/Xe vacuum ultraviolet (VUV) plasma is the blue emitting BaMgAl 10 O 17 :Eu 2 þ (BAM), which undergoes deterioration of color quality and efficiency during panel preparation (thermal damage) and during panel operation (radiation damage). The mechanism of its deterioration has been the subject matter of several research publications [1–7]. How- ever neither compositional variations nor the introduction of trivalent ions into the host lattice has improved significantly the stability of BAM, so far. The solution to this problem apparently lies in finding new materials, which are stable in PDP [8–10]. However, none of the materials developed so far could match with the high quantum efficiency of BAM under VUV excitation (Z 147 ¼ 0.96) [11]. CaWO 4 is the oldest, self-activated blue (broad emission peaking at 420 nm) X-ray image intensifying phosphor still in use for specific applications [12,13]. Its large X-ray absorption is due to the presence of WO 4 . It is a low cost and very stable material. There are other applications of this phosphor. For example, CaWO 4 is occasionally used as the blue phosphor in low pressure Hg-discharge lamps. Rare earth activated tungstates have been found to be suitable as scintillators and laser materials. Recently, CaWO 4 scintillators have been considered as a most suited target material in a cryogenic search for dark matter, since detectors with a CaWO 4 absorbing medium have the capability to discriminate between electron and nuclei recoils by simultaneous detection of scintillation photons and phonons [14]. Lumines- cence properties of CaWO 4 :Eu 3 þ ,Tb 3 þ under VUV excitation have been recently reported [15]. Presently, a comparison of the luminescence efficiencies of self-and Tm-activated CaWO 4 with BAM under VUV excitation will be made. 2. Experimental Self-activated CaWO 4 was made from the following solid state diffusion reaction at high temperatures in air: CaCl 2 þ Na 2 WO 4 -CaWO 4 þ 2NaCl After the above firing, the samples were thoroughly washed in triple distilled water and filtered to remove the water soluble NaCl formed. The firing temperature (950 1C) and firing duration (2 h) were optimized so as to achieve a high fluorescence efficiency. Tm-doped CaWO 4 sample was made with the addition of Tm 2 O 3 (2 mol%). A slight excess quantity of Na 2 WO 4 was usually added so that Tm 2 O 3 could react with it and there is no Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence 0022-2313/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jlumin.2011.03.071 n Corresponding author. Tel.: þ919940597433; fax: þ91 44 26811009. E-mail address: arunachalamlakshmanan@yahoo.com (A. Lakshmanan). Journal of Luminescence 131 (2011) 1625–1628