Fe3+ red phosphors based on lithium aluminates and an aluminum lithium oxyfluoride prepared from LiF as the Li Source

Abstract LiF was used as the Li source to prepare Fe 3+ red phosphors based on lithium aluminates and an aluminum lithium oxyfluoride. LiF led to the three types of the host materials of α-LiAlO 2 , γ-LiAlO 2 and Al 4 LiO 6 F with the different synthetic conditions. Metastable α-LiAlO 2 crystallized up to 800 °C under Li-rich conditions in the starting mixture (eg. LiF/Al(OH) 3 =3). α-LiAlO 2 converted to γ-LiAlO 2 above 800 °C. The flux effect of the excess LiF resulted in the enhancement of the photoluminescence (PL) intensity at higher temperatures with the growth of the crystalline grains of γ-LiAlO 2 :Fe 3+ . The reaction between LiF and γ-Al 2 O 3 at Li/Al=0.25 brought the formation of Al 4 LiO 6 F at 800 °C and above. Red PL from Fe 3+ was observed at ca. 740 nm in γ-LiAlO 2 , 730 nm in α-LiAlO 2 and 690 nm in Al 4 LiO 6 F under the irradiation of ultra-violet (UV) light. They had charge-transfer excitation bands in the UV region and weak excitation bands in the visible region due to the d-d (or ligand field) transition. The red PL in these phosphors originated in the tetrahedrally coordinated Fe 3+ .