Ca<sup>2+</sup>/Si<sup>4+</sup> Modification of the (Gd,Lu)AG Garnet for Enhanced Broadband Cr<sup>3+</sup> Luminescence of High Thermal Stability
Yun Wang, Zhiyuan Pan, Sihan Feng, Lijie Gao, Xuejiao Wang, Qi Zhu, Ji‐Guang Li
Abstract
Near-infrared (NIR)-emitting phosphors with high quantum efficiency and thermal stability are crucial to NIR pc-LEDs. Garnet-structured (GdLuCa)(Al 4– z SiCr z )O 12 ( z = 0.01–0.2) and (Gd 2– x LuCa x )(Al 4.95– x Si x Cr 0.05 )O 12 ( x = 0.2–1.0) new phosphors with promising NIR luminescence under blue light excitation were designed and fabricated by a solid-state reaction in this work. It was analyzed that the Ca 2+, Cr 3+, and Si 4+ ions would replace Gd 3+ in [GdO 8 ], Al1 in [Al1O 6 ], and Al2 in [Al2O 4 ], respectively, and the optimal Cr 3+ content is z = 0.05, above which concentration quenching would occur via an electric dipole–dipole interaction. Increasing Ca 2+ /Si 4+ substitution up to x = 1.0 led to luminescence enhancement by a factor of up to 1.85 and internal/external quantum efficiency (%) increment from ∼25.9/10.7 to 63.4/27.5, and all of the phosphors showed excellent thermal stability ( I 423 K / I 298 K ≥ 87.6%). The luminescence properties of Cr 3+ were discussed in detail through systematic investigation of the effects of Cr 3+ and Ca 2+ /Si 4+ contents on the crystal structure, local coordination, and crystal field. With the NIR pc-LED device integrated from the optimal phosphor ( x = 1.0) and a blue LED chip, electroluminescence manifested potential applications in night vision and medical diagnosis.