Cr3+-Doped Sr1–nBanHfO3 Perovskites: Distinct Evolution of Average Structure and Local Coordination for Tunable Near-Infrared Emission

Cr 3+ -activated perovskite phosphors are promising near-infrared (NIR) emitters, yet their luminescent behaviors are often interpreted primarily in terms of average crystal field effects. Herein, we investigate Sr 1– n Ba n HfO 3 :Cr 3+ as a model system to elucidate the role of local coordination. While synchrotron diffraction reveals a continuous structural evolution from orthorhombic to cubic symmetry with increasing Ba content, Cr K -edge XANES/EXAFS, DFT-assisted local structure analysis, and spectral simulations reveal that the Cr-centered local coordination environment evolves differently from the average crystallographic framework. This difference between average and local structural evolution strongly influences the luminescence behavior, including excitation intensity ratios, R -line evolution, and thermal coupling between the 4 T 2 and 2 E states. Quantitative analysis shows a nonmonotonic variation of C/B , a continuous nephelauxetic trend, and a systematic decrease in both ΔE (E–T) and thermal activation energy ΔE a , indicating that local coordination variation plays a critical role in the excited-state dynamics beyond a simple average crystal-field description. The Sr-rich composition exhibits superior thermal stability and emission efficiency, enabling proof-of-concept phosphor-converted NIR LED (pc-NIR LED) demonstrations for short-range NIR illumination, imaging, and material identification. This work highlights local coordination engineering as a key strategy for designing high-performance NIR-emitting materials.