Abstract
The feasiblity of using Yb2+ as a scintillation sensitiser for CsBa2I5:Sm2+ near-infrared scintillators has been assessed. CsBa2I5 samples with concentrations ranging from 0.3% to 2% Yb2+ and 0–1% Sm2+ have been studied. The scintillation properties have been determined and the dynamics of the scintillation mechanism have been studied through photoluminescence measurements. Radiationless energy transfer between Yb2+ ions plays a key role in increasing the ratio between the spin-forbidden and spin-allowed emission with increasing Yb2+ concentration in samples where Yb2+ is the only dopant. In samples co-doped with Sm2+, the Yb2+ 4f13[F27/2]5d1[LS] and 4f13[F27/2]5d1[HS] states both serve as donor states for radiationless energy transfer to Sm2+ with a rate of energy transfer that is inversely proportional to the luminescence lifetime the respective donor states. At a Sm2+ concentration of 1%, 85% of the Yb2+ excitations are transferred to Sm2+ through radiationless energy transfer. Almost all of the remaining Yb2+ emission is reabsorbed by Sm2+, resulting in nearly complete energy transfer.
Highlights
In the past two decades, extensive scintillation research has been performed on Ce3+ and Eu2+-doped halides [1]
Attaining an energy resolution below 2% requires a scintillator with a light yield superior to that of LaBr3: Ce3+ (60,000 ph/MeV [3]) paired with a detector with high quantum efficiency
The light yield and proportionality requirements are satisfied by some Eu2+-doped halide scintillators, such as CsBa2I5:Eu2+ and SrI2: Eu2+
Summary
In the past two decades, extensive scintillation research has been performed on Ce3+ and Eu2+-doped halides [1]. The light yield and proportionality requirements are satisfied by some Eu2+-doped halide scintillators, such as CsBa2I5:Eu2+ and SrI2: Eu2+. After absorption of a 1 MeV photon, approximately 100,000 electron hole pairs are created in these scintillators [7], indicating that the probability of the creation of an electron hole pair resulting in an excitation of Eu2+ is near unity. Despite this great performance, Eu2+-doped scintillators often suffer from self-absorption, making them less suitable in applications where large crystals are required [8,9,10,11]
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