<p>A series of Lu₂Ge₂O₇: Sm³⁺ phosphors with varying Sm³⁺ dopant concentrations were synthesized via a high-temperature solid-state reaction method. X-ray diffraction (XRD) analysis confirmed the formation of a single-phase Lu₂Ge₂O₇: Sm³⁺ structure, indicating successful incorporation of Sm³⁺ ions into the host lattice. Photoluminescence (PL) spectroscopy was employed to investigate the concentration quenching behavior and thermal stability of the phosphors. Based on the Van Uitert model, it was demonstrated that electric dipole–dipole interactions serve as the primary mechanism for energy transfer among Sm³⁺ ions. Furthermore, detailed temperature-dependent emission studies revealed that the thermal quenching of the Sm³⁺:⁴G_5/2 excited state can be effectively described by a thermally activated cross-relaxation process modeled by the Arrhenius equation. Finally, the optical transition characteristics of Sm³⁺ in Lu₂Ge₂O₇ were systematically analyzed using fluorescence decay measurements in conjunction with Judd–Ofelt theory and diffuse reflectance spectroscopy.</p>