Structure-property correlations in Eu-doped tetra calcium phosphate phosphor: A key to solid-state lighting application

The unique emission characteristics and the crystal structure of Ca-4(PO4)(2)O:Eu2+ were studied. Considerably broad emission from 500 nm to 800 nm was measured at 77 K when the material was excited at 365 nm. Its crystal structure was refined using neutron diffraction, allowing precise and accurate oxygen positions to be determined. This enabled a relationship between the optical properties and the crystal structure crucial for achieving a large redshift of the 5d level of Eu2+ to be established, which is important to match the excitation energy band with near-ultraviolet or blue light-emitting-diodes used for solid-state lighting. The importance of the anion polarizability and the distortion of the coordination polyhedron were also discussed. (C) 2015 Elsevier B.V. All rights reserved.