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Cerium-doped mixed garnet-type single crystals (Gd x Y 1- x) 3 Al 2 Ga 3 O 12 with different yttrium content have been fabricated and studied as a prospective scintillating material enabling improvement of scintillation properties by tuning the composition of the matrix-building crystal. The influence of the matrix composition on the emitting Ce ion is studied using linear and time-resolved nonlinear optical absorption and time-resolved photoluminescence spectroscopy. The study of photoluminescence at resonant excitation revealed a composite origin of Ce3+ emission band. This behavior is interpreted by the contribution of Ce3+ ions located in inequivalent positions expected due to the disorder caused in the garnet-type lattice of a mixed crystal by compositional fluctuations. The substitution of gadolinium by yttrium in the lattice results not only in an emission blue shift and in decreased splitting of the lowest doublet 5d state of Ce3+ but also in an increased separation between the lowest doublet level 5d 1 and the lowest triplet 5d 3 level, as well as in changing the rates of intracenter and extracenter energy relaxation. [Display omitted] • Photoluminescence spectrum is composite due to inequivalent positions of Ce3+ ions. • Decay time of Ce3+ emission decreases from 55 ns at 1.9 eV to 40 ns at 2.5 eV. • Substitution of Gd by Y decreases 5d 1 -5d 2 splitting of Ce3+ and increases 5d 1 -5d 3 separation. • Introduction of Y in GAGG lattice increases Ce3+ intracenter relaxation time. • Capture of trapped electrons to nonradiative recombination centers is enhanced in GYAGG. [ABSTRACT FROM AUTHOR]

A novel technique for testing the timing properties of scintillators is presented. The technique is based on transient absorption (TA) induced in a scintillating material by a selective excitation of the activator ion. A figure of merit to assess the timing properties of scintillators is suggested. This parameter was estimated for a set of cerium doped lutetium–yttrium oxyorthosilicate (LYSO:Ce) bars, which have been fabricated for Barrel Timing Layer sensor of Compact Muon Solenoid detector (CMS BTL) and exhibited different timing properties, and compared with the results obtained by conventional coincidence time resolution (CTR) measurements. The figure of merit applied for the tested bars shows a strong correlation (Pearson's correlation coefficient R = 0.95) with the CTR. These results suggest that the TA technique could be used as an experimental method to expand in a complementary way the extensive qualification procedure of LYSO:Ce crystals that will be performed for the production of the CMS BTL detector. • Coincidence time resolution correlates with activator population rise time. • Population rise time can be probed by transient absorption in femtosecond domain. • Transient absorption can be exploited for testing of scintillator timing properties. [ABSTRACT FROM AUTHOR]

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 Lu 2 SiO 5 :Ce (LSO) and mixed oxyorthosilicate Lu 1.6 Y 0.4 SiO 5 :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. [ABSTRACT FROM AUTHOR]