Overcoming Rigidity‐Flexibility Constraints in Garnet Phosphors for Broadband and Thermally Stable NIR Emission

Achieving near‐infrared (NIR) phosphors with broadband emission, robust thermal stability, high internal quantum efficiency (IQE), and excellent chemical durability remains a longstanding challenge, largely due to the fundamental trade‐off between structural rigidity and flexibility. Here, we overcome this constraint by designing a novel series of garnet‐type phosphors, BaY 2 Ga 4‐ x GeO 12 : x Cr 3+ (BYGG: x Cr 3+ ). The optimized composition BYGG:0.06Cr 3+ delivers an IQE of 93%, remarkable anti‐thermal quenching behavior (103% emission retention at 423 K), and outstanding chemical stability (retaining 97% emission after 35 days in water). Notably, fine‐tuning the Cr 3+ concentration broadens the emission bandwidth from 77 to 194 nm while preserving strong thermal stability (93%@423 K). This exceptional performance arises from the synergistic combination of ultra‐high structural rigidity (Debye temperature, Θ D = 987 K), wide bandgap (5.10 eV), weak crystal field strength, and optimized 4 T 2 excited‐state population. A fabricated NIR phosphor‐converted LED (pc‐LED) device demonstrates an NIR radiated power of 189.35 mW at 100 mA and a photoelectric conversion efficiency up to 12%. These results establish NIR phosphor BYGG: x Cr 3+ as a promising candidate for next‐generation NIR pc‐LED applications in night vision, non‐destructive inspection, and biomedical imaging.