Improvement of the timing properties of Ce-doped oxyorthosilicate LYSO scintillating crystals

• Published in: The Journal of physics and chemistry of solids Vol. 139; p. 109356
• Main Authors: Tamulaitis, G., Auffray, E., Gola, A., Korzhik, M., Mazzi, A., Mechinski, V., Nargelas, S., Talochka, Y., Vaitkevičius, A., Vasil'ev, A.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-04-2020
• ISSN: 0022-3697; 1879-2553
• DOI: 10.1016/j.jpcs.2020.109356

The aim of this work has been to improve the time resolution of radiation detectors for future high-energy physics experiments and medical imaging applications. Ce-doped oxyorthosilicate Lu2SiO5:Ce (LSO) and mixed oxyorthosilicate Lu1.6Y0.4SiO5:Ce (LYSO) have been investigated as prospective scintillators for such high-time-resolution applications. A differential optical absorption technique with sub-picosecond time resolution upon selective excitation of Ce3+ ions to different excited states has been adopted to study carrier dynamics in these scintillators, and coincidence time resolution measured using 511 keV γ-quanta has been exploited to test their timing properties. A delay in population of the emitting level of Ce3+ has been observed, and is interpreted in terms of electron trapping, which is more pronounced in mixed yttrium-containing LYSO crystals due to composition fluctuations. It is shown that the delay, which affects the luminescence response time, can be eliminated by co-doping of LYSO:Ce with calcium at concentrations as low as 5 ppm. The faster kinetics of electron transfer correlates with a better coincidence time resolution. Thermalization and spatial distribution of non-equilibrium carriers has been studied theoretically to link the results obtained by the time-resolved differential optical absorption technique with the behavior of the non-equilibrium carriers generated by irradiation.
•The time resolution of LYSO is more affected by carrier trapping than that of LSO.•Carrier trapping in LYSO is enhanced by fluctuations in the compound composition.•Ca-co-doping, even at a concentration of 5 ppm, improves the response time of LYSO:Ce.•Femtosecond pump-probe spectroscopy is a useful tool for improving Ce-doped scintillators.