Investigation of crystal structure and associated electronic structure of Sr6BP5O20 |
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Authors: | Helmut Ehrenberg PC Schmidt R McSweeney KC Mishra |
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Institution: | a Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt, Germany b Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Petersenstr. 20, 64287 Darmstadt, Germany c Precision Materials and Components, OSRAM SYLVANIA, Hawes Street, Towanda, PA 18848, USA d Central Research, OSRAM SYLVANIA, Beverly, MA 01915, USA |
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Abstract: | Strontium borophosphate phosphate (Sr6BP5O20, SrBP), activated by divalent europium ions is a bluish-green phosphor emitting in a broad band with the emission peak near 480 nm. In this paper, we report the crystal structure of SrBP determined from an analysis of the X-ray diffraction pattern of a prismatic single crystal (size 60 μm×50 μm×40 μm). This crystal was chosen from undoped phosphor powder samples prepared for this purpose by solid-state reaction. SrBP is observed to crystallize in a body-centered tetragonal lattice with the lattice parameters and , the associated space group being (space group 120). Using the structural data from this study, we have also calculated its electronic structure using the augmented spherical wave method and the local density approximation (LDA). We show the ordering of the electronic states by the density of states (DOS) and the partial DOS plots. The LDA gives a direct optical band gap at the Γ point of about 5 eV. The significance of the crystal structure and associated electronic structure is discussed with respect to maintenance of this phosphor in Hg-discharge lamps. |
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Keywords: | Phosphor Fluorescent lamps CRI lamps Host material Strontium borophosphate phosphate Divalent europium ions Crystal structure Single-crystal X-ray diffraction Synchrotron powder diffraction Thermal expansion Electronic structure calculation Band structure calculation |
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