Properties and mechanisms of scintillation in CsGd₂F₇:Ce³⁺ and CsY₂F₇:Ce³⁺ crystals

The scintillation properties of Ce³⁺ doped CsGd₂F₇ and CsY₂F₇ crystals have been studied at various temperatures. Upon X-ray excitation CsY₂F₇:5 mol% Ce³⁺ shows fast ( tau approximately=32 ns) Ce³⁺ 5d to 4f luminescence with a yield of 1400 photons MeV^-1 at room temperature. The most intense Ce³⁺ luminescence of about 7300 photons MeV^-1 is found in CsGd₂F₇:20 mol% Ce³⁺. The scintillation decay curve of CsGd₂F₇:Ce³⁺ consists of at least two non-exponential components, one of the order of tens of nanoseconds and one in the microsecond region. Both CsY₂F₇ and CsGd₂F₇ show a broad STE emission band at around 445 nm, especially at low temperatures. VUV photon excitation measurements at 300 K and low temperatures revealed the presence of two inequivalent types of Ce³⁺ centres in both CsY₂F₇ and CsGd₂F₇. The presence of Gd³⁺ appears to have a dominating influence on the luminescence characteristics of CsGd₂F₇:Ce³⁺, due to the occurrence of both Ce³⁺ to Gd³⁺ and Gd³⁺ to Ce³⁺ energy transfer as well as energy migration over the Gd³⁺ sublattice. On the basis of the optical studies, models of the scintillation mechanisms of CsY₂F₇ and CsGd₂F₇ are developed which account for the scintillation properties of these crystals.