The crystal structures and fluorescent properties of BaLu1.95Ce0.05Al4-xGaxSiO12 (1≤x≤2.5) solid solutions

Abstract

Currently, the green and cyan emitting phosphors are indispensable for white LEDs with high color rendering index. However, the phosphors which can be effectively excited by blue light and have excellent thermal stability are numbered. Here, a series of new solid solutions of BaLu1.95Ce0.05Al4-xGaxSiO12 (1 ≤ x ≤ 2.5) was successfully synthesized by the conventional solid-state reaction method. Their crystal structures and fluorescent properties are investigated systematically. BaLu1.95Ce0.05Al4-xGaxSiO12 (1 ≤ x ≤ 2.5) crystallized in the cubic system with the space group Ia3‾d. All the O resides at Wyckoff position 96h. Ba/Lu/Ce (Wyckoff position 24c) and O form a dodecahedron, Al/Ga (Wyckoff position 16a) and O make up an octahedron, Al/Ga/Si (Wyckoff position 24d) and O constitute a tetrahedron. The unit cells are composed by the dodecahedrons, octahedrons and tetrahedrons. It is found that BaLu1.95Ce0.05Al3GaSiO12 and BaLu1.95Ce0.05Al2.5Ga1.5SiO12 have extra-high quantum yield and excellent thermal stability of fluorescence. Their quantum yield excited by 448 nm blue light exceeds 97%. At 150 °C, their emission intensity can remain more than 92% of that at 25 °C. As the temperature rises from 25 to 200 °C, their emission color shifts are very small. The white LED lamp fabricated by using the BaLu1.95Ce0.05Al2.5Ga1.5SiO12 phosphor exhibits outstanding optical properties with Ra = 92.4, CRI = 90.1, CCT = 4593 K and CIE 1931 chromaticity values as (x = 0.3513, y = 0.3221). All the experimental data demonstrates that BaLu1.95Ce0.05Al3GaSiO12 and BaLu1.95Ce0.05Al2.5Ga1.5SiO12 have great application prospects in white LEDs as cyan-green phosphors.