Synthesis and enhancement of luminescence intensity by co-doping of M + (M = Li, Na, K) in Ce 3+ doped strontium haloborate A.B. Gawande a,1 , R.P. Sonekar b,⇑ , S.K. Omanwar a a Department of Physics, SGB Amravati University, Amravati 444602, (M.S.), India b Department of Physics, G.S. College, Khamgaon, (M.S.), India article info Article history: Received 29 December 2013 Received in revised form 17 February 2014 Accepted 18 February 2014 Available online 6 March 2014 Keywords: Strontium haloborate Charge compensation Photoluminescence abstract Photoluminescence properties of Ce 3+ doped strontium haloborates synthesized by solution combustion technique were studied. Sr 2 B 5 O 9 Cl:Ce 3+ produce emission band peaking at 345 nm under 307 nm excita- tion radiation. Enhancement of luminescence intensity was observed when M + (Li + , Na + ,K + ) ions were used as co-dopant in Sr 2 B 5 O 9 Cl:Ce 3+ . Charge compensation by Na + ion in Sr 2 B 5 O 9 Cl:Ce 3+ show strongest luminescence intensity at 345 nm under 307 nm excitation radiation. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Materials of composition M 2 B 5 O 9 R:Eu 2+ (M = Sr, Ba) gained special attention because of possible applications as storage phos- phors for X-ray imaging [1] and thermal neutron detection [2]. Ce 3+ doped alkaline earth haloborates can be of importance for practical applications as storage phosphors. The substitution of a trivalent ion for an alkaline earth ion requires the presence of a charge com- pensator to maintain the overall charge neutrality of the crystal. In view of its spectroscopic characteristics, the Ce 3+ seems to be a suitable ion for study of the charge compensation mechanism for trivalent cations. Machida et al. [3] briefly described the crystal structure of Sr 2 B 5 O 9 R (R = Cl, Br) and conclude that crystal struc- ture of Sr 2 B 5 O 9 R (R = Cl, Br) is almost similar to Eu 2 B 5 O 9 Br. The structures consist of a three-dimensional (B 5 O 9 )1 network in which three unique BO 4 tetrahedra and two unique BO 3 triangles are linked together. The metal ions can occupy two different C1 crystallographic sites in the host (at room temperature), and in each case the ion is surrounded by seven oxygen and two halide atoms. The actual coordination geometry of the two metal sites is that of a distorted heptagonal bipyramid, with the two halide ions at the axial positions and equatorial O atoms at the joint of the bipyramid. The two axial halides bridge to neighbouring bipyr- amids. The metal and halide ions are located alternately along the tunnels of the (B 5 O 9 )1 network, forming linear chains along the a-(b-) axis for site 1 (2). Thus, the metal ions in site 1 (2) are isolated from neighbouring metal ions by the borate units of the (B 5 O 9 )1 network in b and c directions (a and c directions) and halide ions in the a-axis (b-axis) direction. It is generally accepted that this structure and those of M 2 B 5 O 9 Cl (M = Ca, Sr, Ba) do not significantly differ, not withstanding their different space groups. In both the orthorhombic (Pnn2) and tetragonal (P42212) struc- tures the metal occupies two inequivalent sites of both C1 (Pnn2) or both C2 (P42212) symmetry [4]. In this work, we discussed the synthesis of Sr 2 B 5 O 9 Cl:Ce 3+ by using solution combustion synthesis technique, which can be potentially used in preparing the phosphors and intensity enhancement by using Li + , Na + or K + as charge compensator. 2. Experimental Sr 2 B 5 O 9 Cl:Ce 3+ and Sr 2 B 5 O 9 Cl:Ce 3+ ,M + (M = Li, Na or K) phos- phors were prepared by solution combustion synthesis technique, discussed in detail in our previous work [5–8]. The method based on exothermic reaction in which ammonium nitrate used as oxi- dizer and urea is used as fuel. The stoichiometric amounts of high purity (Analytical Reagent) starting materials Sr(NO 3 ) 2 , Ce(NO 3 ) 3 , H 3 BO 3 , NH 4 Cl, CO(NH 2 ) 2 , NH 4 NO 3 have been used for preparation of phosphors. The stoichiometric amount of starting materials with little amount of double distilled water were mixed thoroughly in an alumina basin to obtain homogeneous solution. The excess water was removed by slow heating (at 70 °C) and the solution then transferred directly to the pre-heated furnace (550 ± 10 °C) http://dx.doi.org/10.1016/j.optmat.2014.02.017 0925-3467/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +91 9422883314. E-mail addresses: gawandeab@gmail.com (A.B. Gawande), sonekar_rp@yahoo.com (R.P. Sonekar). 1 Tel.: +91 9404689773. Optical Materials 36 (2014) 1143–1145 Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat