Yun Wang,Zhiyuan Pan,Sihan Feng,Lijie Gao,Xuejiao Wang,Qi Zhu,Ji-Guang Li
Near-infrared (NIR)-emitting phosphors with high quantum efficiency and thermal stability are crucial to NIR pc-LEDs. Garnet-structured (GdLuCa)(Al4–zSiCrz)O12 (z = 0.01–0.2) and (Gd2–xLuCax)(Al4.95–xSixCr0.05)O12 (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 Ca2+, Cr3+, and Si4+ ions would replace Gd3+ in [GdO8], Al1 in [Al1O6], and Al2 in [Al2O4], respectively, and the optimal Cr3+ content is z = 0.05, above which concentration quenching would occur via an electric dipole–dipole interaction. Increasing Ca2+/Si4+ 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 (I423 K/I298 K ≥ 87.6%). The luminescence properties of Cr3+ were discussed in detail through systematic investigation of the effects of Cr3+ and Ca2+/Si4+ 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.
Spectral coverage and saturability within 700–1100 nm of phosphor-converted near infrared light-emitting-diodes (pc-NIR LEDs) are crucial for the practical applications in bioimaging, food quality analysis and night vision fields, while developing ultra-broadband NIR phosphors are still a challenge. Herein, we reported a broadband NIR phosphor LiInP 2 O 7 : Cr 3+ in phosphate system. The emission spectrum of this phosphor covers 700–1200 nm with a full width at half maximum (FWHM) of 165 nm and an emission peak centering at 860 nm under 460 nm excitation. This broadband emission is verified to be derived from 4 T 2 g → 4 A 2 g transition of Cr 3+ in a single crystal site. To further expand the emission spectrum , Cr 3+ →Yb 3+ energy transfer in LiInP 2 O 7 was designed, and an ultra-broadband emission with a FWHM of 225 nm was obtained through appropriate amount of Yb 3+ codoping. The energy transfer efficiency can reach as high as 81% in this material. Furthermore, the energy transfer mechanism, quantum yield , thermal stability and fabrication performance were investigated in detail, demonstrating the ability of achieving ultra-broadband and efficient NIR emission of LiInP 2 O 7 : Cr 3+ , Yb 3+ phosphor material.
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