Tuning the Near Infrared Emission of MgO:Cr³⁺ Phosphors by Inducing Ti⁴⁺ Ions

Near-infrared (NIR) phosphors activated by Cr³⁺ ions hold significant potential for applications such as night vision and plant growth lighting due to their tunable emission properties governed by crystal field (CF) strength. In this study, Cr³⁺ and Ti⁴⁺ co-doped MgO phosphors were synthesized via a high-temperature solid-state reaction to modulate the NIR emission. Structural and optical characterizations revealed that Ti⁴⁺ incorporation enhances the CF strength (Dq/B ratio increases from 2.4 to 2.6), inducing a blue shift in the emission peak from 810 (MgO:Cr³⁺) to 780 nm (Mg_0.8Ti_0.2O:Cr³⁺) and with a strong sharp emission at 720 nm. The Ti⁴⁺ doping also increases the fluorescence lifetime from 150.9 to 816.4 μs, attributed to altered Cr³⁺ occupancy in octahedral sites and modified spin-allowed transitions. These findings demonstrate that Ti⁴⁺ co-doping effectively tunes the NIR emission of MgO:Cr³⁺ phosphors, offering a promising strategy for designing wavelength-adjustable NIR light sources.