Tunable Near‐Infrared Emission via Crystal Field Engineering in Blue‐Excitable In ³⁺ ‐Substituted MgGa ₂ O ₄ :Cr ³⁺ ,Ni ²⁺ Phosphors

ABSTRACT Engineering the local crystal field through cation substitution is a widely adopted strategy to modulate the emission wavelength of transition‐metal‐doped inorganic phosphors in the near‐infrared (NIR) region. While redshifting emission is desirable for extending applications into long NIR wavelengths, excessive shifts often lead to increased nonradiative losses due to large Stokes shifts, posing a trade‐off between spectral tunability and luminescence efficiency. Herein, we present two series of In 3+ ‐substituted phosphors, MgGa 1.94 − x In x O 4 :0.06Cr 3+ and Mg 0.98 Ga 1.94 − x In x O 4 :0.06Cr 3+ ,0.02Ni 2+ , with 0.1 ≤ x ≤ 0.9. The incorporation of large In 3+ results in lattice expansion and enhanced local disorder, considerably affecting the crystal field environment of Cr 3+ and Ni 2+ . In the first part of the study, the effect of cation substitution on the complex luminescence behavior of Cr 3+ in these partially inverse spinel phosphors is systematically investigated. Subsequently, the role of In 3+ in tuning the Cr 3+ /Ni 2+ ‐codoped MgGa 2 − x In x O 4 system, wherein Ni 2+ emission is successfully redshifted from 1269 to 1429 nm, is explored. The findings of this work underscore the dual role of In 3+ as both a structural modulator and an emission‐tuning agent, offering a promising strategy for the rational design of broadband, wavelength‐adjustable NIR phosphors.