Ca[LiAl₃N₄]:Eu²⁺A Narrow-Band Red-Emitting Nitridolithoaluminate

Abstract

Ca­[LiAl₃N₄]:Eu²⁺ is an intriguing new narrow-band red-emitting phosphor material with potential for application in high-power phosphor-converted light-emitting diodes (pc-LEDs). With excitation by blue InGaN-based LEDs, the compound exhibits an emission maximum at 668 nm with a full width at half maximum of only 1333 cm^–1 (∼60 nm). Ca­[LiAl₃N₄]:Eu²⁺ was synthesized from Ca, LiAlH₄, LiN₃, AlF₃, and EuF₃ in weld-shut Ta ampules, and the structure was solved and refined on the basis of single-crystal X-ray diffraction data. After isotypical crystallization with Na­[Li₃SiO₄], the compound forms a highly condensed framework of AlN₄ and LiN₄ tetrahedra [<i>I</i>4₁/<i>a</i> (no. 88), <i>Z</i> = 16, <i>a</i> = 11.1600(16) Å, and <i>c</i> = 12.865(3) Å] and can thus by classified as a nitridolithoaluminate. Both types of polyhedra are connected to each other by common edges and corners, yielding a high degree of condensation, κ = 1. The Ca site is positioned in the center of <i>vierer</i> ring channels along [001] and coordinated in a cuboidal manner by eight N atoms. To validate the presence of Li, transmission electron microscopy (TEM) investigations employing electron energy-loss spectroscopy (EELS) were carried out. Furthermore, to confirm the electrostatic bonding interactions and the chemical composition, lattice energy calculations [Madelung part of lattice energy (MAPLE)] have been performed