Manipulating Persistent Luminescence via Chemical Unit Cosubstitution in Gallate Spinel Li _{1– <i>x</i>} Mg _{2 <i>x</i>} Ga _{5– <i>x</i>} O ₈ :Cr ³⁺ Solid Solution

Near-infrared (NIR) persistent luminescence (PersL) materials have garnered significant interest over recent decades due to their potential applications in bioimaging, nocturnal surveillance, and data encryption. Despite progress in steady-state NIR luminescence, designing materials with tunable near-infrared afterglow and dynamically controllable emission remains challenging. This study presents a series of NIR PersL solid solutions, referred to as Li1–xMg2xGa5–xO8:Cr3+, synthesized through high-temperature solid-state reactions. Modification of the composition through the chemical unit cosubstitution of Li+–Ga3+ units in solid solutions with Mg2+–Mg2+ counterparts facilitates the modulation of emission in the deep-red and NIR spectral regions, attributed to the characteristic Cr3+ transitions of the 2E → 4A2 and 4T2 → 4A2. These solid solutions derived from gallate spinels, specifically MgGa2O4:Cr3+ and LiGa5O8:Cr3+, were investigated to elucidate the correlation between structural characteristics and luminescent properties, as well as to explore the variations in trap distribution and density resulting from compositional alterations. This research illustrates the cosubstitution of chemical units in the advancement of NIR persistent phosphors, thereby promoting further exploration of luminescent materials with distinctive properties.