S. Neicheva

Confocal Microscopy of Luminescence Inhomogeneity in LGSO:Ce Scintillator Crystal

Confocal microscopy was exploited to study spatial distribution of luminescence characteristics in Lu2SiO5:Ce (LSO:Ce) and mixed Lu2xGd2-2xSiO5:Ce (LGSO:Ce) crystals. Spatial distributions of spectrally-integrated photoluminescence (PL) intensity, PL band peak and spectral center of mass positions, and band width were determined. In both crystals, the luminescence spectra at 405 nm excitation are dominated by one broad band peaked at ~ 510 nm, while a long-wavelength shoulder is also observed in LGSO:Ce. Spatial inhomogeneities of the order of 1-3 micron in diameter are observed for the band position in LGSO:Ce. A comparative analysis of the spectra shows that the inhomogeneity is caused by spatial distribution in the spectral component at 500-700 nm, which may be attributed to Ce3+ located in CeO6 polyhedra (Ce2), or, more probably, to some defects in the crystal. Our results indicate that the changes in luminescence spectrum shape reflect Lu/Gd ratio fluctuations on a micrometer scale in the bulk of the mixed LGSO:Ce crystals.

Energy Relaxation in LSO and LGSO Crystals Studied in the VUV Range

The role of energy transfer from Gd3+ to Ce3+ activator in the formation of the luminescence yield and kinetics of Lu2xGd2-2xSiO5:Ce (LGSO) mixed crystals has been studied by VUV spectroscopy including temperature dependent time-resolved measurements of luminescence excitation and emission spectra and luminescence kinetics in the excitation energy range 4 to 25 eV at the SUPERLUMI station of HASYLAB, DESY. Improved scintillation yield as well as suppressed afterglow that can be achieved by appropriate choice of Lu/Gd ratio as well as of Ce-concentration were suggested to result from an additional channel of energy relaxation via Gd-states, which appears in LGSO. The role of Ca-codoping is discussed.