Luminescence kinetics in Ce-doped TbxGd3−xAl5O12 garnet with various terbium content

In view of the current demand for fast scintillators for ionizing radiation detectors for high-energy physics experiments and medical imaging, the excitation transfer between host crystal and activator ions in activated scintillators is an increasingly important phenomenon. The current study is focused on the excitation transfer in Ce-doped terbium gadolinium aluminum garnets with different ratios of Tb and Gd ions in the host lattice. Scanning electron microscopy and cathodoluminescence images show that the liquid phase epitaxy (LPE) using PbO-B₂O₃ flux ensures the fabrication of thin single-crystalline films of such scintillators of high structural homogeneity. Time-resolved photo- and cathodo-luminescence spectroscopy of the films revealed that the electron transfer from activator ion Ce³⁺ to the nearest lattice-building ions Tb³⁺ is faster than vice versa. The acceleration of the decay of Ce³⁺ luminescence by the introduction of Tb is demonstrated, whereas the Tb³⁺ ions emit prompt photons in the subnanosecond domain, but this emission is strongly quenched by nonradiative recombination. We show that the excitation transfer from Ce³⁺ to the closest Tb³⁺ is the dominant mechanism accelerating the emission decay of Tb_xGd${}_{3-x}$Al₅O₁₂:Ce operating as a scintillator.