Optimising synthesis conditions for long lasting SrAl 2 O 4 phosphor B. Faridnia and M.M. Kashani Motlagh Chemistry Department, Iran University of Science and Technology, Tehran, Iran, and A. Maghsoudipour Ceramic Department, Materials and Energy Research Center, Karaj, Iran Abstract Purpose – To evaluate the effect of flux, activator and co-activator on solid state synthesis of SrAl 2 O 4 : Eu 2 þ , Dy 3 þ phosphor, where boric oxide, europium oxide and dispersium oxide were used, respectively. Design/methodology/approach – To optimise synthesis condition of long lasting phosphorescence SrAl 2 O 4 phosphor, boric oxide was used as a flux. To improve relative intensity of SrAl 2 O 4 : Eu 2 þ phosphor, the critical concentration of Eu 2 þ was determined. The effect of various concentration of co- activator on afterglow properties, the effect of Dy 3 þ ion on the emission and excitation spectra were examined. Findings – The SrAl 2 O 4 : Eu 2 þ , Dy 3 þ phosphor powders have been synthesised by solid state reaction method. The result of XRD patterns indicated that, addition of 5 mol% B 2 O 3 enhanced the formation of SrAl 2 O 4 at 1,2008C. Investigation on the variation of emission intensity of different phosphors containing different amounts of Eu 2 þ revealed that after 6 mol% of Eu 2 þ concentration, quenching process occurred. Dy 3 þ formed trap levels and results demonstrated that increasing concentration of Dy 3 þ up to 5 mol% reduced the relative intensity and increased the decay time. Originality/value – Using B 2 O 3 as a flux and solid state reaction method for preparation of this phosphor is in good agreement with industrial production and make it economic, because of reduced sintering temperature. Keywords Fluxes, Solid state physics Paper type Research paper Introduction Strontium aluminate (SrAl 2 O 4 ) has been proven to be an efficient host material with a broad band emissions (Suematsu et al., 2002; Niittykoski et al., 2002) The host belongs to the three-dimensional frame work which consists of corner – sharing AlO 4 tetrahedrons with zigzag strings and each oxygen is shared with two aluminum ions so that each tetrahedron has one net negative charge. Charge balance is completed by the large divalent cation Sr 2 þ , which occupies interstitial sites within the tetrahedral frame work. The tetrahedronal anion group (AlO 4 ) is helpful towards the existence of the deoxidised ions (e.g. Eu 2 þ , Ce 3 þ , Pr 3 þ , Tb 3 þ ) (Kutty and Nag, 2003, 2004; Wang et al., 1998; Ravichandran et al., 1999). The luminescence of the Eu 2 þ ion in inorganic hosts has been investigated during the last three decades. The phosphorescence of Eu 2 þ in most hosts is believed to be caused by the 4f 6 5d 1 ! 4f 7 transition. The peak position in the emission spectra strongly depends on the nature of the Eu 2 þ surrounding, and therefore, Eu 2 þ ions can emit different visible lights in various crystal fields. It has broad band luminescence spectrum with emission wavelengths extending from the UV to the red portions of the spectrum (Niittykoski et al., 2001; Katsumata et al., 1998; Kato et al., 1999; Peng et al., 2004; Aitasulo et al., 2003). The Eu þ 2 emissions from many phosphor hosts are intense enough to find important applications, e.g. in fluorescent lamps, plasma displays, luminescence clocks and watches and sign roads (Ravichandran et al., 1999; Niittykoski et al., 2004; Hase and Aziz, 2001). Kutty et al. (Kutty and Nag, 2003, 2004; Luo et al., 2006), have studied the effect of boric oxide on the afterglow properties, luminescence intensity and persistent time of SrAl 2 O 4 : Eu 2 þ , Dy 3 þ phosphor. Chang et al. (2003) also investigated phase compositions and luminescence properties in detail, as well as the role of flux in the reaction process and its contribution to long lasting property. As mentioned in many references (Hase and Aziz, 2001; Cordoncillo et al., 2003; Niittykoski et al., 2004; Kutty and Nag, 2004; Uehara and Ochi, 2001), boric oxide has been used as a fluxing agent for recrystallisation and grain growth, implying that B 2 O 3 is a non – reactive medium to alkaline earth aluminates. In the work reported here, in order to prepare SrAl 2 O 4 : Eu 2 þ , Dy 3 þ phosphor and to characterise relevant phosphorescence, we optimised the firing temperature, amount of B 2 O 3 as a flux, amount of Eu 2 þ as activator and amount of Dy 3 þ as co-activator in SrO · Al 2 O 3 host lattice. Experimental Materials The starting powders were Al 2 O 3 (Merck, 101095), SrCO 3 (Merck, 7861), B 2 O 3 (Merck, 163), Eu 2 O 3 (Merck, ZA2534156436) and Dy 2 O 3 (Merck, ZA3758651415). The current issue and full text archive of this journal is available at www.emeraldinsight.com/0369-9420.htm Pigment & Resin Technology 36/4 (2007) 216–223 q Emerald Group Publishing Limited [ISSN 0369-9420] [DOI 10.1108/03699420710761816] 216