Site Occupation Strategy for Tunable Ultra‐Broadband Emission in Cr ³⁺ ‐Doped Near‐Infrared Phosphors and High‐Efficiency Optoelectronic Applications

ABSTRACT Cr 3+ ‐activated broadband near‐infrared (NIR) luminescent materials have attracted widespread attention due to their unique photophysical properties, and phosphor‐converted NIR light‐emitting diodes (pc‐LEDs) are an ideal light source with non‐destructive penetration, medical diagnostics, and night vision. This paper reports a novel garnet‐type Cr 3+ ‐activated (Ca 3‐ x Sc x )(Sc 2‐ x Mg x )Ge 3 O 12 NIR broadband phosphor via chemical substitution. The incorporation of Mg 2+ leads to [Mg 2+ /Sc 3+ ] substitution for [Sc 3+ /Ca 2+ ], which is revealed using formation energy and tolerance factor calculations. The phosphors exhibit broadband emission spanning 600–1400 nm with the occupation of both dodecahedral and octahedral sites in the crystal, and (Ca 1 Sc 2 )(Mg 2 )Ge 3 O 12 :Cr 3+ has the widest full width at half maximum (FWHM) of 242 nm. Moreover, due to electronegativity effects, the emission undergoes a significant redshift with increasing x in (Ca 3‐ x Sc x )(Sc 2‐ x Mg x )Ge 3 O 12 . The sample (Ca 3‐ x Sc x )(Sc 2‐ x Mg x )Ge 3 O 12 with x = 1 demonstrates good thermal stability (79%@375 K), while x = 0 exhibits excellent thermal stability (97%@375 K). The fabricated NIR pc‐LED exhibits outstanding optical performance, demonstrating potential applications in anti‐counterfeiting, non‐destructive testing, and bioanalysis.