Speaker
Description
Recently, oil well logging in the shale layer that exists at a depth greater than conventional oil resources have been required due to increase oil demand. Operating in a deep underground region at high temperature, the scintillator is required that a high light output can be maintained even at high temperature. In previous study, our group has been investigated Ce-doped (Gd,La,Y)2Si2O7, and the light output (LO) at high temperature was improved compared to before Y-admixed [1]. However, in that paper, we have not revealed the reason why LO at high temperature was improved. As the improvement factors, we considered (i) to extend the bandgap and energy gap between top of 5d1 level and bottom of the conduction band (CB) which contribute to suppress the thermal quenching, (ii) to generate new electron trap(s) under Ce3+ 5d1 level moderately, and contribute to be increased the LO at high temperature. In this study, to find the improvement factor of LO at high temperature, we evaluated band structure, the temperature dependence, traps for Y admixed Ce:La-GPS.
UV absorption spectra of (Ce0.01 Gd0.59-x La0.4 Yx)2Si2O7 (x=0.00, 0.05, 0.10 and 0.15) grown by the micro-pulling-down method were measured to calculate the bandgap energy. Thereafter, we estimated the temperature dependence of photoluminescence (PL) intensity and LO excited by a Xe lamp and 137Cs as gamma-rays source, respectively, and evaluated electron trap. In addition, we measured thermoluminescence glow curve within 6-300 K.
From the results of bandgap energies, the bandgap energies were almost constant regardless of Y concentration, and the effect of the bandgap energy on temperature dependence of LO was considered slightly. On the other hand, comparing the temperature dependence of PL intensity and scintillation LO, where all values were normalized to each value at 298 K, the scintillation normalized LO of Y 5% or 10% admixed samples at 448 K were higher than that of PL intensity. From those result, some electron traps were generated, and would contribute to the temperature dependence. The above results and the detail are shown in this presentation.
[1] T. Horiai, A. Yoshikawa, et al., Temperature dependence of Y, La-admix gadolinium pyrosilicate scintillator, presented at The 10th Asian Meeting on Electroceramics, Dec. 2016, Taipei, Taiwan.
