A novel efficient broadband near-infrared phosphor LiGaGe2O6:Cr3+ with EQE enhancement and spectral tuning by Sc3+–Ga3+ substitution for NIR pc-LED application

Abstract

Most of the NIR emitting materials reported until now are limited by their low external quantum efficiency. Developing highly efficient and tunable broadband near-infrared phosphors remains a significant challenge for realizing their multi-applications. Herein, a gallate, LiGaGe₂O₆, was selected as the host for Cr³⁺ doping, while its crystal and electronic structures were revealed using the Rietveld refinement and DFT calculations. On irradiating this LiGaGe₂O₆:Cr³⁺ phosphor with 460 nm blue light, it generates a broadband NIR emission (λ_em = 830 nm) covering the 700–1200 nm region with a full width at half maximum of 192 nm. A promising external quantum efficiency (EQE) of 27.9% could be achieved at an optimal Cr³⁺ content of 0.06. It was found that a spectral tuning with the peak position in the range of 830–890 nm was realized by the Sc³⁺–Ga³⁺ substitution with a decreasing crystal field strength. Meanwhile, the optimized Li(Ga_0.24Sc_0.70)Ge₂O₆:Cr³⁺ exhibited an enhanced EQE of 47.8%. The variation of emission thermal stability by Sc³⁺ substitution was investigated. The prepared phosphor-converted light-emitting diode (pc-LED) device generated an intense NIR emission (25.3 mW at 100 mA) with a photoelectric efficiency of 10%. Thus, this work not only provides a novel high-performance broadband NIR phosphor for NIR pc-LED, but also demonstrates that cationic substitution is an effective strategy to tune and enhance the NIR optical properties of Cr³⁺-doped phosphors.