Ultrawide NIR-II Emission Regulation of Ni2+ in SrGa12O19 Based on a Crystal-Field Engineering Strategy

Near-infrared II light (NIR-II, 1000–1700 nm) is highly desirable for deep-tissue bioimaging, nondestructive testing, and night vision, but it remains challenging to realize simultaneously tunable emission peak and bandwidth within a single-activator system. Ni2+ with a 3d8 configuration is a promising broadband NIR-II activator ion whose emission originates from crystal-field-dependent d-d electron transitions. Nevertheless, the currently reported Ni2+-activated phosphors are largely limited with spectral tunability (full width at half-maximum, fwhm <200 nm). Herein, a series of SrGa12O19:Ni2+ phosphors with NIR-II emission are prepared that exhibit an emission peak at 1180 nm originating from the 3T2g → 3A2g electron transition. Through designing Al3+-Ga3+ cation substitution strategy, the local coordination environment and crystal-field strength around Ni2+ are controllably modulated, driving a progressive redshift of the emission peak from 1180 to 1350 nm and a pronounced fwhm broadening from 222 to 566 nm, ultimately affording an ultrabroadband NIR-II emission. Furthermore, a prototype phosphor-converted light-emitting diode (LED) is fabricated, demonstrating promising applications in night vision. This crystal-field engineering strategy substantially extends the tunable range of the emission peak and fwhm for Ni2+-activated phosphors and provides guidelines for optimizing transition-metal-activated NIR luminescent materials.