A New Host Compound of Aluminum Lithium Fluoride Oxide for Deep Red Phosphors based on Mn~(4+), Fe~(3+) and Cr~(3+)

摘要

A new host compound of an aluminum lithium fluoride oxide (ALFO) was proposed for deep red phosphors based on the luminescent centers of Mn~(4+), Fe~(3+), and Cr~(3+). The characterization brought an estimated composition of Al_4LiF_(0.1)O_(6.45), indicating that fluorine was largely lost during the heat-treatment in spite of the expected composition of Al_4LiFO_6 from the starting mixture. ALFO was a disordered spinel compound whose structure was different from ordered inverse-spinel LiAl_5O_8 with respect to the cation arrangement. In ALFO, Li~+ and Al~(3+) were statistically distributed over the tetrahedral and octahedral sites in the spinel-type lattice. Each luminescent center of Mn~(4+), Fe~(3+), and Cr~(3+) led to deep red emission in ALFO and the disordered nature of the crystal structure remarkably enhanced the luminescence of Mn~(4+) compared to Mn~(4+) in Li Al_5O_8. Among these luminescent centers, the emission peak of Mn~(4+) arose on the shortest wavelength side with the peak top at 661 nm. Fe~(3+) and Cr~(3+) showed, respectively, the rather broad peak centering around 690 nm and the characteristic twin peak with the tops at 705 and 715 nm.