Abstract
The influence of co-doping of Gd3Al2GA3O12:Ce (GAGG:Ce) scintillator with magnesium on the rise time of luminescence response was studied in two GAGG:Ce crystals grown in nominally identical conditions except of Mg co-doping in one of them. Time-resolved photoluminescence spectroscopy and free carrier absorption techniques were exploited. It is evidenced that the Mg co-doping decreases the rise time down to sub-picosecond domain. Meanwhile, the light yield decreases by ∼20%. Thus, the feasibility of exploitation of the fast rise edge in luminescence response for ultrafast timing in scintillation detectors is demonstrated. The role of Mg impurities in facilitating the excitation transfer to radiative recombination centers is discussed.
Highlights
The improvement of time resolution down to ∼10 ps is currently one of the hottest topics in the development of radiation detectors based on scintillation crystals [1]
The fast detector response is necessary to prevent the pile-up effect in high-luminosity high-energy physics experiments [2] as well as to enable the decrease of the dose injected to a patient in medical imaging, in particular, in time-of-flight positron emission tomography (TOF-PET) [3] and positron annihilation lifetime spectroscopy (PALS) [4]
Co-doping by Mg results in unstructured enhancement of the absorption in the high-energy part of the spectrum. The absorption in this spectral region might be attributed to the broad band due to the charge transfer transition of Ce4+ stabilized by aliovalent doping of divalent magnesium [15,16], though the close values of the absorption coefficients in the band due to 4f-5d1 transition in both samples shows that only a small part of Ce3+ is converted into Ce4+ state in the co-doped crystal
Summary
The improvement of time resolution down to ∼10 ps is currently one of the hottest topics in the development of radiation detectors based on scintillation crystals [1]. To study the capability of scintillators to serve in fast radiation detectors, the emission decay time and the rise time of their luminescence response is being currently reinvestigated. Due to a high light yield of up to 50000 ph/MeV, a short luminescence decay time (< 100 ns) [12], and good matching of the emission band with the sensitivity spectrum of conventional SiPMs, GAGG:Ce is a promising scintillation material for certain particle physics experiments and might compete with Ce-doped LYSO and LSO crystals in TOF-PETs. the luminescence rise time of this scintillator is of special importance. To compare the PL response kinetics with the time evolution of the density of nonequilibrium carriers, free carrier absorption (FCA) has been investigated in these two samples by using pump and probe configuration ensuring sub-picosecond time resolution
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