Time-resolved luminescence and excitation spectroscopy of Co-doped Gd3Ga3Al2O12 scintillating crystals

Cerium doped Gd₃Ga₃Al₂O₁₂ (GGAG) single crystals as well as GGAG:Ce single crystals co-doped by divalent (Mg²⁺, Ca²⁺) and tetravalent (Zr⁴⁺, Ti⁴⁺) ions have been studied by means of time-resolved luminescence as well as the excitation luminescence spectroscopy in vacuum ultraviolet (VUV) and soft X-ray (XUV) spectral range. Tunable laser excitation was applied for time-resolved experiments in order to obtain luminescence decay curves under excitations in Ce³⁺, Gd³⁺ and excitonic absorption bands. The influence of the co-dopant ions on the Ce³⁺ luminescence decay kinetics is elucidated. The fastest luminescence decay was observed for the Mg²⁺ co-doped crystals under any excitation below bandgap energy indicating the perturbation of the 5d states of Ce³⁺ by Mg²⁺ ions. Synchrotron radiation was utilized for the luminescence excitation in the energy range from 4.5 to 800 eV. Special attention was paid to the analysis of Ce³⁺ excitation spectra in VUV and XUV spectral range where multiplication of electronic excitation (MEE) processes occur. Our results demonstrated that GGAG:Ce single crystals co-doped by Mg²⁺ ions as well as the GGAG:Ce crystal annealed in vacuum reveal the most efficient excitation of Ce³⁺ emission in VUV-XUV excitation range. The role of intrinsic defects in MEE processes in the co-doped as well as in the annealed GGAG:Ce single crystals is discussed.