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Growth and luminescent properties of Ce and Ce-Tb doped (Y,Lu,Gd)2SiO5:Ce single crystalline films
|Yuriy V. Zorenko 1, Vitaliy Gorbenko 2, Volodymyr Savchyn 2, Tetyana Zorenko 2, Boris Grinyov 3, Oleg Sidletskiy 3, Alexander Fedorov 3|
1. Instytut Fizyki, Uniwersytet Kazimierza Wielkiego w Bydgoszczy (UKW), Powstancow Wielkopolskich, Bydgoszcz 85-822, Poland
The single crystalline films (SCF) of undoped, Ce and Ce-Tb doped Y2SiO5 (YSO), Lu2SiO5 (LSO) and (LuxGd1-x)2SiO5 (LGSO) orthosilicates with a thickness from 2.5 to 100 µm were prepared by the liquid phase epitaxy (LPE) method onto undoped YSO and LSO substrates with different orientation from melt-solution (MS) based on PbO-B2O3 flux. These SCF can be used as scintillating screens for 2D X-ray microimaging . In case LSO and LGSO SCF growth onto YSO and LSO substrates we did not use any additional doping to reduce the misfit between the SCF and substrate lattice parameters.
Luminescence of undoped YSO and LSO SCF is caused by the UV emission of Pb2+ flux impurity in the bands at 365 and 348 nm, respectively, related to the 3P1,0-1S0 transitions, and by a visible band at 445 and 438 nm, ascribed to luminescence of excitons localised around the Pb2+ centers.
The luminescent properties of YSO:Ce, LSO:Ce and LGSO:Ce SCFs were compared with YSO, LYSO and LSO:Ce single crystal (SC). We found that the luminescence of YSO:Ce and LSO:Ce SCF caused by the 5d1-4f radiative transition of Ce3+ ions is red-shifted in comparison with SC counterparts. This shift can be caused by (1) different relative occupancy of Y1/Lu1 and Y2/Lu2 sites of YSO and LSO hosts by Ce3+ ions in the case of SCF and SC growth due to very different temperatures for SC (2100oC) and SCF (~1000oC) crystallization; (2) luminescence of Pb2+ centers, overlapping with the emission of Ce3+ ions. We also found that the emission spectrum of LGSO:Ce SCF is systematically red-shifted with respect to spectrum of LSO:Ce SCF with increasing the Gd content in range of 0-0.7 formula units due to the increasing of the relative content of Ce2 centers in LGSO host. Such a red shit of the luminescence spectra of LGSO:Ce SCF is accompanied by decreasing their light yield (LY) down to 65 % for Lu0.3Gd0.7SO:Ce SCF in comparison with LY of LSO:Ce SCF. We would like also to note that LGSO:Ce SCF, despite of lower LY in comparison with LSO:Ce, possess much higher signal/noise ratio due to drop of afterglow level by ~100 times, by analogy with SC . Therefore, image contrast at X-ray visualization should be better with LGSO screens.
The LY of YSO:Ce and LSO:Ce SCF reaches the value equal to 95-145 % of that for a LSO:Ce SC under excitation by α–particles of Am241 sources (5.5 MeV) but only ~40-60 % of the LY of high-quality LYSO:Ce SC. The lower LY of (Y,Lu,Gd)SO:Ce SCF with respect to the best SC analogues is caused by quenching induced by Pb2+ flux impurity. Therefore, the usage of the lead-free fluxes is strongly needed for crystallization by the LPE method of (Y.Lu,Gd)SO:Ce SCF scintillators to increase their LY.
 T. Martin, at al. IEEE TNS 56 (2009) 1412.
 O. Sidletskiy et al. Journal of Crystal Growth 312 (2010) 601-606
Presentation: Poster at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 10, by Yuriy V. Zorenko
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17
Submitted: 2013-04-13 19:26 Revised: 2013-07-30 09:40