A New Host Compound of Aluminum Lithium Fluoride Oxide for Deep Red Phosphors Based on Mn⁴⁺, Fe³⁺, and Cr³⁺

Abstract

A new host compound of an aluminum lithium fluoride oxide (ALFO) was proposed for deep red phosphors based on the luminescent centers of Mn4+, Fe3+, and Cr3+. The characterization brought an estimated composition of Al4LiF0.1O6.45, indicating that fluorine was largely lost during the heat-treatment in spite of the expected composition of Al4LiFO6 from the starting mixture. ALFO was a disordered spinel compound whose structure was different from ordered inverse-spinel LiAl5O8 with respect to the cation arrangement. In ALFO, Li+ and Al3+ were statistically distributed over the tetrahedral and octahedral sites in the spinel-type lattice. Each luminescent center of Mn4+, Fe3+, and Cr3+ led to deep red emission in ALFO and the disordered nature of the crystal structure remarkably enhanced the luminescence of Mn4+ compared to Mn4+ in LiAl5O8. Among these luminescent centers, the emission peak of Mn4+ arose on the shortest wavelength side with the peak top at 661 nm. Fe3+ and Cr3+ showed, respectively, the rather broad peak centering around 690 nm and the characteristic twin peak with the tops at 705 and 715 nm.