Photoluminescence and afterglow tuning in ultra-broadband near-infrared Mg3Y2Ge3O12:Cr3+ phosphor via cation substitution

Broadband near-infrared (NIR) long-persistent phosphors with adjustable optical property have been urgently demanded for practical applications in bio-imaging and plant cultivation. Herein, Cr3+ doped Mg3Y2Ge3O12 garnet phosphors with ultra-broadband NIR emissions (600−1200 nm) peaked at 776 nm were prepared via a high-temperature solid-state reaction method, and the cation sites for Cr3+ were well identified and assigned based on the Rietveld refinement and time-resolved emission spectra (TRES). Under the excitation at 436 nm, wide-range modulations in intensity, wavelength (763−834 nm) and bandwidth (143−227 nm) of 4T2→4A2 (4F) transition were achieved via Zn2+/Ca2+ substitution, which completely covers the maximum absorption ranges (715−1050 nm) of bacteriochlorophyll from anaerobic photosynthetic bacteria (PSB). According to the classic Tanabe-Sugano theory, the crystal field parameters around different Cr3+ centers were calculated to explain the spectral tailoring effect. Meanwhile, the afterglow duration was greatly improved from 2 min to 66 and 240 min after co-doping Zn2+/Ca2+, and the trap distribution and mechanism was elaborately explored via thermos-luminescence (TL) experiments. Above results provide an effective strategy for designing NIR-emitting phosphors with desired optical and afterglow performance, which well meets the light requirements of diverse applications especially in plant growth.