Nonstoichiometric Strategy for Enhancing Luminescence Performance of Cr 3+ ‐Activated Ca 3 Ga 2 Ge 3 O 12 Broadband NIR Phosphors

ABSTRACT Near‐infrared (NIR) emitting phosphors with broadband emission enable their promising application in various fields. In this work, a series of Ca 3 Ga 2 Ge 3‐ x O 12‐δ :Cr 3+ NIR phosphors were synthesized to investigate the influence of Ge 4+ vacancies on the structural and luminescent properties. X‐ray diffraction analysis confirms that the main garnet phase is retained at low vacancy concentrations, whereas minor impurity phases appear at higher x values. X‐ray photoelectron spectroscopy analysis reveals the presence of both GaO 6 and GeO 6 octahedrons in this garnet. Under 458 nm excitation, all samples exhibit a broad NIR emission band centered at 752 nm. The integrated emission intensity increases with Ge 4+ vacancy concentration, reaching a maximum at x = 0.4. The optimized phosphor shows exceptional thermal stability, retaining 91.4% of its room‐temperature intensity at 423 K. This study demonstrates that Ge 4+ vacancy engineering is an effective strategy for enhancing the NIR luminescence of Cr 3+ ‐doped garnet phosphors.