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

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 (lambda(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(Ga0.24Sc0.70)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.