Scintillation mechanisms of cerium-doped rare earth oxyorthosilicates

Citation

Suzuki, Hideyuki (1994) Scintillation mechanisms of cerium-doped rare earth oxyorthosilicates. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3a2x-nk63. https://resolver.caltech.edu/CaltechETD:etd-10182005-130418

Abstract

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Rare earth oxyorthosilicates (RE)2(SiO4)O (RE = rare earth) have high densities and effective atomic numbers for efficient gamma-ray detection. Among these, Gd2(SiO4)O, Y2(SiO4)O and Lu2(SiO4)O have no absorption lines at visible wavelengths and thus were examined as potential single crystal scintillators by doping with cerium (Ce).

The light emission mechanism of the activator Ce3+ ion in (RE)2(SiO4)O was investigated with UV light, by selectively exciting absorption bands of Ce3+ at low temperature (~11 K). It was found that all three compounds have two types of excitation and emission spectra and decay constants, and they were attributed to two Ce3+ centers (Ce1 and Ce2) occupying two different host rare earth sites.

The origins of two decay constants in the gamma-ray excited decay of Gd2(SiO4)O:Ce (GSO) were investigated. We focused on GSO since the gamma-ray excited decay times of GSO are much slower than the intrinsic Ce3+ decay, in contrast with Y2(SiO4)O:Ce and Lu2(SiO4)O:Ce. Since Gd3+ emission bands overlap Ce3+ absorption bands, the energy transfer from Gd3+ to Ce3+ was analyzed for a possible explanation for the slow Ce3+ decays. The Gd3+ absorption bands in the UV region were excited by a synchrotron light source and the Ce3+ decay was monitored. With excitation into the [...] and [...] states of Gd3+, a slow decay component and a build-up were observed in the Ce3+ decay, consistent with energy transfer from [...] and [...] states of Gd3+ to Ce3+.

The energy migration through the Gd sublattice in GSO was investigated. The Gd was diluted by optically inactive rare earths, Y and Lu, and the macroscopic energy transfer rate from Gd3+ to Ce3+ was measured as a function of Gd concentration. The results show that the macroscopic transfer rate from Gd3+ to Ce3+ increases as Gd concentration increases, indicating that the energy of the excited Gd3+ can migrate through the Gd sublattice before one of the Gd3+ near a Ce3+ can transfer its energy to the Ce3+.

Thesis Files