The Effect of Boron on Processing and Phosphorescence Behavior of SrAl 4 O 7 (SA 2 ) Co-doped with Eu 2+ and Dy 3+
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The Effect of Boron on Processing and Phosphorescence Behavior of SrAl4O7 (SA2) Codoped with Eu2+ and Dy3+ Murat G. Eskin, Hasan Kurt, Mehmet Ali Gulgun and Cleva W. Ow-Yang Faculty of Engineering and Natural Sciences, Sabanci University, Orhanli, Tuzla, Istanbul, 34956, TURKEY. ABSTRACT SrAl4O7 (SA2) phosphor powders were synthesized by using a modified Pechini process. Varying amounts of boron was incorporated into the SA2 lattice to investigate the effects on crystal structure and optical properties. X-ray spectra showed that boron addition enhances phase purity of the powder at a calcination temperature of 1000 °C, whereas the formation of a new S4A7 phase was induced when a calcination temperature of 1100 °C was used. The afterglow duration was extended to longer than 5 hours when boron was present in 4-11 mol%. To elucidate the enhanced optical properties, interband trap characteristics were studied by thermoluminescence and photoluminescence. INTRODUCTION While phosphors have traditionally played an important role in lighting technology, more recent developments in long persistence aluminate host materials have be realized in safety lighting, such as back-up solutions for power outages [1]. Phosphorescence is the delayed (~10 ns or longer) emission of light during the de-excitation of an electron. Whereas a short afterglow duration would be sufficient for conventional lighting applications, extended phosphorescence would enable broader use of energy-efficient safety lighting, including garments worn by relief workers and larger area building surfaces. Boron oxide is a common sintering flux and was used in the production of alkali aluminate phosphors by conventional solid state reaction. In 2003, Nag and Kutty noted that the presence of B was associated with persistence of over 5 hours in Eu2+ and Dy3+ co-doped strontium aluminate (SA) powders [2]. However, the role of B in dramatically enhancing the afterglow duration is still unknown. In previous work by our group [3], we have demonstrated a solution polymerization method for producing boron-incorporated, Eu2+ and Dy3+ co-doped SrAl4O7 (SA2ED), with enhanced afterglow persistence and intensity. Beyond merely the optical properties, surprisingly high amounts of boron could be incorporated into the SA lattice. To clarify how boron is entering into the doped SA2ED lattice and the nature of its impact on the phosphorescence duration, the crystal structure and electronic structure have been investigated. In this paper, we present further details from our investigation of the role of boron in SA2ED. Perturbations to the crystal structure and electronic structure will be discussed. EXPERIMENT Phosphorescent powders of 1 mol% Eu2+ and 1 mol% Dy3+ co-doped SrAl4O7 (SA2ED) were synthesized by using a modified Pechini process, a solution polymerization technique in which chelating agents are used to assist in the assembly of the crystal lattice. Surprisingly high amounts of boron can be incorporated into the SA2 structure [3], without disturbing the phase purity of the
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