Tailoring Excited Bands and Impurity‐Host Interactions for Efficient NIR Emissions in Cr ³⁺ ‐Activated Perovskite Ca ₂ Ga _1‐ <i> _x </i> In <i> _x </i> NbO ₆

ABSTRACT Engineering the coupling between host‐lattice phonons and doped Cr 3+ ions is pivotal for regulating optical properties of broadband near‐infrared (NIR) phosphorsand prompting their applications. Here, we investigate Ca 2 Ga 0.99‐ x In x NbO 6 :0.01Cr 3+ ( x = 0‐0.99) phosphors to elucidate how Ga/In substitution‐induced B‐site disorder tunes the crystal structure, vibrational modes, Cr 3+ excited bands, and excitation‐relaxation dynamics. A gradual evolution from an ordered framework to a disordered one is revealed through XRD, Raman, and 71 Ga ssNMR measurements, resulting in symmetry breaking and activation of low‐frequency phonons. The PLE spectra demonstrate composition‐driven tuning of the host‐Cr 3+ hybridized excited bands, yielding two dominant peaks at ∼385 and 460 nm for x = 0.495, which match well with commercial UV and blue LEDs emissions, enabling dual‐mode excitation. Huang‐Rhys factor S ≈ 3.8 for ion‐lattice coupling and Dq / B ≈ 2.05 for crystal field effect are determined by fitting the phonon sidebands using the multimode Brownian oscillator model and Tanabe‐Sugano model analysis. It is further shown that increasing In 3+ content strengthens phonon‐assisted nonradiative relaxation within the split 4 T 2 ( 4 F) manifold, thereby resulting in thermal redistribution of luminescence intensity and shortened lifetimes. Overall, adjusting B‐site disorder provides an effective handle to engineer impurity‐host interactions and tailor the performance of Cr 3+ ‐activated NIR phosphors.