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

A mechanism of firefly high-scintillation light yield (LY) of Tb-doped quaternary (Gd, Y)(3)Al2Ga3O12 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 2E(g). The cascade of photons is explained by combining three factors: first, the high quantum yield Q approximate to 1 of the luminescence at excitation in lower mixed states 4f(7)5d(1) with high spin (HS) and low spin (LS); second, the cross-relaxation 4f(7)(P-6)5d(1)(HS) -> 4f(7)(S-8)5d(1)(HS) provides the excitation of 4f(8)(F-7(0)) -> 4f(8)(D-5(1,4)) transition of the 4f(8) configuration of the same or neighboring Tb ion, which is followed by the luminescence from D-5(1,4); and finally, the relaxation of 4f(7)(S-8)5d(1-5)(HS) configuration into the excited 4f(8) configuration occurs with future emission from 4f(8)(D-5(1,4)) 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.

Automated summary

This study reports a mechanism of firefly high-scintillation light yield (LY) in terbium-doped quaternary garnet ceramics. The luminescence excitation efficiency is defined through measurements with the synchrotron source, showing a quantum yield Q > 1 below the photon multiplication energy range. The cascade of photons is explained by the high quantum yield of the luminescence at excitation in lower mixed states, the cross-relaxation providing the excitation transition, and the relaxation of configuration that leads to future emission.