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Recently, Ce:(La, Gd)$_2$Si$_2$O$_7$ (Ce:La-GPS) scintillator was reported the have a good energy resolution (FWHM) of ~5% at 662 keV, and its light output remained constant up to 150 $^{\circ}$C (423K) [1,2]. Moreover, we grew larger size Ce:La-GPS crystals by Czochralski process up to 2 inch diameter and studied their scintillation properties. Up to now, we have shown the scintillation properties of fixed La-concentration, and we have never revealed the La-concentration dependence of some properties such as bandgap energy, light output at high temperatures, rising time, etc. In this paper, we show the Comprehensive study on La-GPS scintillator with a La concentration of 20 – 50% in the Gd site.
Ce-doped and pure Ce:(La$_x$, Gd$_{1-x}$)$_2$Si$_2$O$_7$ crystals were grown by the micro-pulling down method from the starting materials: 99.99% pure Gd$_2$O$_3$, La$_2$O$_3$, SiO$_2$ and CeO, where x = 0.2 to 0.5. The crystals were confirmed to have single phase using X-ray diffraction patterns.
For Ce-doped samples, after cutting and polishing the samples, transmittance and photo-luminescence (PL) excitation and emission spectra were measured using a spectrophotometer (V-530, JASCO) and a spectrofluorometer (FLS920, Edingurgh Instrument: EI) with Xe lamp (EI, Xe-900), respectively. The pulse height spectra at the high temperature up to 200 $^{\circ}$C (473K) were measured with a ruggedized PMT (Hamamatsu R1288AH) in order to evaluate the temperature dependence. To evaluate the bandgap energy, transmittance spectra of pure La-GPS samples were measured at low temperature (7K) using a beam-line at a synchrotron faculty, Ultraviolet Synchrotron Radiation Facility (UVSOR), in Japan.
We found that both samples had almost the same emission and excitation spectra and good light output over 150$^{\circ}$C (423K). The band gap energies did not depend on the La-concentration, and the energies were estimated to be around 7.1 – 7.2 eV. We show the above results, rising time for the samples and the temperature dependence of light output or intensity from 7 to 500K in this presentation.
[1] A. Suzuki, S. Kurosawa, and A. Yoshikawa et al., Appl. Phys. Express 5 (2012) 102601.
[2] S. Kurosawa, and A. Yoshikawa et al., NIMA 772 (2015) 72.
