First Observation of the Scintillation Cascade in Tb3+‐Doped Quaternary Garnet Ceramics

Abstract

A mechanism of firefly high‐scintillation light yield (LY) of Tb‐doped quaternary (Gd, Y)3Al2Ga3O12 garnet ceramics is reported. Through measurements with the synchrotron source, the high efficiency of the luminescence excitation, providing a quantum yield Q > 1 below the photon multiplication energy range, is defined. The excitation efficiency reaches two at the excitation energy slightly above 2Eg. The cascade of photons is explained by combining three factors: first, the high quantum yield Q ≈ 1 of the luminescence at excitation in lower mixed states 4f75d1 with high spin (HS) and low spin (LS); second, the cross‐relaxation 4f7(6P)5d1(HS) → 4f7(8S)5d1(HS) provides the excitation of 4f8(7F0) →4f8(5D1,4) transition of the 4f8 configuration of the same or neighboring Tb ion, which is followed by the luminescence from 5D1,4; and finally, the relaxation of 4f7(8S)5d1‐5(HS) configuration into the excited 4f8 configuration occurs with future emission from 4f8(5D1,4) states. This cascade forms the final stage of the scintillation in the compound being studied and provides a LY twice as high compared with the material when doped with Ce.