Thermally Robust Broadband NIR-II Emission Enabled by Dual-Site Ni2+ Occupancy in Double Perovskite

Broadband and thermally robust near-infrared (NIR) emitters are essential for advanced photonic applications from night-vision imaging to biological sensing and spectroscopy. However, transition-metal-activated phosphors face an intrinsic coupling between emission bandwidth and thermal stability, with ultrabroad spectra accompanied by severe thermal quenching. Here, we demonstrate a dual-site occupancy strategy mitigating this trade-off by enabling Ni 2+ to occupy two crystallographically distinct octahedral sites in double perovskite Ca 2 AlTaO 6 . The optimized Ca 2 AlTaO 6 :Ni 2+ phosphor exhibits broadband NIR-II emission (1050–1650 nm) with a 225 nm full width at half maximum, retaining 61% of room-temperature luminescence intensity at 423 K. Spectral deconvolution, lifetime analysis, and structural characterization reveal the concentration-dependent emission peak red-shift (1260 → 1310 nm) originates from dynamic Ni 2+ redistribution between the two sites, with controllable spectral broadening. This site-selective emission mechanism provides a reliable route for tunable NIR-II spectral engineering. A phosphor-converted LED based on a commercial red excitation chip delivers efficient NIR-II output, validated in night-vision imaging, biological tissue transillumination, and qualitative chemical identification. These results establish dual-site occupancy as a viable, generalizable design principle for broadband, thermally stable NIR emitters, with direct relevance to photonic light-source engineering.