Terbium-doped gadolinium garnet thin films grown by liquid phase epitaxy for scintillation detectors

Abstract

Single-crystal films of terbium-doped gadolinium gallium garnet (Gd₃Ga₅O₁₂:Tb) were grown by the isothermal dipping liquid phase epitaxy method on undoped (111)-oriented GGG substrates using PbO/B₂O₃ as a solvent. The effect of the Tb³⁺ doping level (2 to 10 at%) on the growth parameters, structure, composition, morphology, and emission properties of the films under optical and X-ray excitation was systematically studied. The saturation temperature increased almost linearly with the Tb content. The Tb³⁺-doped films exhibit a very low lattice mismatch of less than 0.05% with respect to the GGG substrate. The dopant ions are uniformly incorporated in the layers, with a segregation coefficient close to unity. The conversion efficiency of the films is optimized for a doping level of 6 at% Tb³⁺ in the solution, reaching a maximum light output of 52% with respect to a reference bulk YAG:Ce crystal. The green emission of Tb³⁺ ions at 543 nm matches with the maximum of sensitivity of CCD/CMOS sensors. The luminescence lifetime of the ⁵D₄ Tb³⁺ emitting state amounts to ∼2.3 ms and is weakly dependent on the doping level. Minimum afterglow intensities are reached for the GGG:Tb films, as compared to other currently employed scintillators. Gd₃Ga₅O₁₂:Tb single-crystalline films represent a viable solution for developing novel scintillators providing high efficiency and sub-μm spatial resolution for X-ray imaging.