Unraveling Broadband Near-Infrared Luminescence in Cr 3+ -Doped Ca 3 Y 2 Ge 3 O 12 Garnets: Insights from First-Principles Analysis.

In this study, we conducted an extensive investigation into broadband near-infrared luminescence of Cr 3+ -doped Ca 3 Y 2 Ge 3 O 12 garnet, employing first-principles calculations within the density functional theory framework. Our initial focus involved determining the site occupancy of Cr 3+ activator ions, which revealed a pronounced preference for the Y 3+ sites over the Ca 2+ and Ge 4+ sites, as evidenced by the formation energy calculations. Subsequently, the geometric structures of the excited states 2 E and 4 T 2 , along with their optical transition energies relative to the ground state 4 A 2 in Ca 3 Y 2 Ge 3 O 12 :Cr 3+ , were successfully modeled using the ΔSCF method. Calculation convergence challenges were effectively addressed through the proposed fractional particle occupancy schemes. The constructed host-referred binding energy diagram provided a clear description of the luminescence kinetics process in the garnet, which explained the high quantum efficiency of emission. Furthermore, the accurate prediction of thermal excitation energy yielded insights into the thermal stability of the compound, as illustrated in the calculated configuration coordinate diagram. More importantly, all calculated data were consistently aligned with the experimental results. This research not only advances our understanding of the intricate interplay between geometric and electronic structures, optical properties, and thermal behavior in Cr 3+ -doped garnets but also lays the groundwork for future breakthroughs in the high-throughput design and optimization of luminescent performance and thermal stability in Cr 3+ -doped phosphors.