Temperature-Dependent Luminescence and Defect Recombination Pathways in As-Grown Gd₃Ga₅O₁₂ Single Crystals

The intrinsic defect-related luminescence of as-grown Gd3Ga5O12 (GGG) single crystals was investigated using synchrotron excitation in the vacuum-ultraviolet region. The photoluminescence spectrum at 7 K exhibits a broad emission band centered near ~2.5 eV (≈500 nm), accompanied by narrow 4f–4f transitions of uncontrolled Tb3+ impurity ions. Gaussian decomposition of the broad band reveals three components at approximately 3.05, 2.70, and 2.50 eV, attributed to self-trapped excitons (STE), antisite-associated recombination, and F/F+-type oxygen-vacancy centers, respectively. Temperature-dependent photoluminescence measurements show that the defect-related luminescence is governed by two thermally activated nonradiative channels with activation energies of ~5–8 meV and 42–56 meV. The shallow channel dominates at 20–50 K, while the main quenching occurs between 100 and 150 K, leading to nearly complete suppression of the broad emission at room temperature. The present results therefore characterize the emission behavior of intrinsic, shallow defect centers in as-grown GGG and contribute to understanding defect recombination pathways that are critical for optimizing garnet-based scintillation and photonic materials.