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Scintillation crystals convert energy of ionizing radiation to ultra-violet or visible light, and are widely used in radiation detectors. In particular, oxide scintillators are chemically stable and have been well investigated. Recently, Ce-doped (La,Gd)2Si2O7 (Ce:La-GPS) scintillators have attracted much attention due to their excellent scintillation properties (high light output, fast decay time and good thermal stability). In previous studies, the luminescence and scintillation properties of Ce:La-GPS with various La concentration such as 9.0, 23.5, 30.0 and 48.0 mol% have been reported [1-3]. For better understanding of the luminescence phenomena in Ce:La-GPS, we grew Ce:La-GPS single crystals with systematically changing La concentration and investigated their luminescence and its thermal stability.
The single crystal growth was performed by micro-pulling-down method . We succeeded in growing transparent (Ce0.015 Lax Gd0.985-x)2Si2O7 single crystals with La concentrations in the range of 0.20-0.60 mol (with increments of 0.05 mol). In order to evaluate the luminescence properties, the photoluminescence (PL) excitation and emission spectra were measured. From the results of the PL spectra at 7 K, the emission wavelength was shifted to shorter wavelength with increasing the La concentration. Considering the ionic radii of La3+ (1.160 Å, C.N.=8) and Gd3+ (1.053 Å, C.N.=8), the average ionic radius of Ce:La-GPS increases as the La concentration increases. Due to the composition change the effect of the crystal field becomes smaller and the emission wavelength shifts to the shorter wavelength. In addition, the PL decay curves excited by nanosecond pulsed light emitting diodes were measured to estimate the thermal quenching. These PL decay curves were fitted with a single-barrier model to evaluate the activation energy of the thermal quenching and the thermal quenching temperature. It was found that both of the activation energy and the quenching temperature increased with increasing La concentration.
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