Crystal-Field-Weakening Engineering Unlocks Ultra-Efficient Eu²⁺ Near-Infrared Emission for Emerging Spectroscopic...

Eu²⁺ ion has emerged as a promising blue-light-excitable near-infrared (NIR) emitter owing to its parity-allowed 5d → 4f transition. However, achieving efficient Eu²⁺ NIR luminescence remains a great challenge due to the large Stokes shift. Conventional strategies rely on strengthening the crystal field to redshift the emission, but this inevitably enhances electron-phonon coupling, promoting non‑radiative multiphoton relaxation and ultimately compromising efficiency, creating an intrinsic trade‑off between emission wavelength and luminescence efficiency. Herein, we break this trade‑off by proposing a crystal‑field‑weakening engineering strategy that reduces the Stokes shift and suppresses non-radiative relaxation, thereby significantly enhancing NIR emission in Ca₃ScHfAlSi₂O₁₂: Eu²⁺. The optimized phosphor exhibits a record internal quantum efficiency of 69.7% at 780 nm under blue excitation, along with high thermal stability (76% retention at 120°C). Mechanistic studies reveal that both intracenter relaxation within Eu²⁺ excited states and energy migration between neighboring Eu²⁺ ions are substantially suppressed, collectively boosting the NIR radiative efficiency. Finally, a blue-light-pumped pc-NIR-LED is fabricated, delivering a high NIR output power of 101.52 mW at 350 mA, and demonstrating promising potential in plant lighting, night vision imaging and non‑destructive testing. This work establishes crystal‑field weakening as a promising design paradigm for high‑performance Eu²⁺‑based NIR phosphors.