Ca²⁺/Si⁴⁺ Modification of the (Gd,Lu)AG Garnet for Enhanced Broadband Cr³⁺ Luminescence of High Thermal Stability

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.