La ³⁺ Vacancy Mediated Enhancement of Near‐Infrared Emission in Cr ³⁺ ‐Activated La ₂ MgTiO ₆ Phosphors for Multifunctional Applications

Near‐infrared (NIR) phosphors with broadband and efficient emission are pivotal for the performance of NIR phosphor‐converted light emitting diodes (pc‐LEDs). In this study, the double perovskite phosphor La 2 MgTiO 6 :Cr 3+ phosphor with broadband emission in the range of 650–950 nm was prepared. To enhance its luminescence, La 3+ vacancy was intentionally introduced into the host lattice. The successful incorporation of vacancies and the increased defect concentration were confirmed by the ratio of adsorbed oxygen to lattice oxygen, Raman spectroscopy, and electron paramagnetic resonance measurements. The existence of La 3+ vacancy was directly verified by spherical aberration‐corrected transmission electron microscopy. As a result, both the emission intensity and thermal stability were improved significantly, achieving a high internal quantum efficiency of 77.8% for the optimized phosphor. We further explored the multifunctional application of the optimized phosphor La 1.8 MgTiO 6‐ δ :Cr 3+ , demonstrating its utility in temperature sensing and NIR pc‐LED devices. This study establishes cation vacancy creation as a powerful and generalizable strategy for optimizing luminescent materials.