Synthesis and characterization of ultraviolet-emitting cerium-ion-doped SrBPO 5 phosphors
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The synthesis and characteristics of strontium borate phosphate phosphors doped with cerium ions were investigated in this study. The synthesis of Sr0.95Ce0.05BPO5 in oxidizing atmosphere results in partial conversion of Ce4+ ions into Ce3+ ions. The luminescent characteristics reveal that Ce3+ ions occupy two principal sites in the host. The dominant emission at 317 nm on 275-nm excitation is attributed to Ce3+ ions located at Sr2+ sites without local charge compensation. The weak emission at 330 nm due to 295-nm excitation is ascribed to Ce3+ ions located at Sr2+ sites in association with charge compensatory vacancy. The reduction of Ce4+ ions to Ce3+ ions occurs in Sr0.95Ce0.05BPO5 heated in the reducing atmosphere. For Sr0.9Ce0.05Na0.05BPO5 and Sr0.9Ce0.05Li0.05BPO5 phosphors, enhancement in luminescence is observed due to the codoping of monovalent ions. The increased luminescence of these phosphors is attributed to the decrease in non-radiative energy transfer. I. INTRODUCTION
The unique spectroscopic properties of rare-earth ions in different host lattices have prompted the development of a variety of materials for diverse applications including lamp phosphors, cathode ray tube phosphors, radiation monitoring, lasers, and scintillators. New matrices doped with rare earths are attracting much attention because of their potential for industrial applications. Recently, a strontium borate phosphate (SrBPO5) host matrix having a crystal structure corresponding to mineral stillwellite was investigated.1–5 The focuses of these SrBPO5 related studies include luminescent properties of Eu2+ and Ce3+ ions in the material,1,2 synthesis via hydrothermal method,3 x-ray photoelectron studies,4 and VUV excited luminescence.5 Research on cerium-ion doped materials is important because these materials have great potential to be applied in the nuclear and lighting industry. The efficient absorption and luminescent properties of trivalent cerium ions (Ce3+) due to their parity allow f → d transitions. These ions serve as sensitizers for transferring energy to other codoped luminescent centers.6,7 The utility of cerium-ion based phosphors is affected by the possible formation of Ce4+ ions during synthesis. The stabilization of Ce4+ ions in the host matrix reduces the luminescence output by depleting Ce3+ ions and by quenching the luminescence a)
Address all correspondence to this author. e-mail: [email protected] b) Permanent address: Radiochemistry Division, B.A.R.C., Trombay, Mumbai, 400085, India. DOI: 10.1557/JMR.2004.0303 2336
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J. Mater. Res., Vol. 19, No. 8, Aug 2004 Downloaded: 11 Mar 2015
of Ce3+ ions through a non-radiative pathway provided by Ce4+ ions. The reduction of trivalent rare-earth ions to their divalent form was reported during synthesis in oxidizing atmosphere under specific conditions.8–11 The primary interest of the present work is to explore the stability of cerium ions in different oxidation states during synthesis in the oxidizing/reducing atmosphere. The effects of
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