Crystal‐Field‐Weakening Engineering Unlocks Ultra‐Efficient Eu ²⁺ Near‐Infrared Emission for Emerging Spectroscopic Applications

Abstract

ABSTRACT Eu 2+ ion has emerged as a promising blue‐light‐excitable near‐infrared (NIR) emitter owing to its parity‐allowed 5d → 4f transition. However, achieving efficient Eu 2+ 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 Ca 3 ScHfAlSi 2 O 12 : Eu 2+ . 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 Eu 2+ excited states and energy migration between neighboring Eu 2+ 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 Eu 2+ ‑based NIR phosphors.