87 research outputs found
Avoiding concentration quenching and self-absorption in Cs4EuX6 (X = Br, I) by Sm2+ doping.
The benefits of doping Cs4EuBr6 and Cs4EuI6 with Sm2+ are studied for near-infrared scintillator applications. It is shown that undoped Cs4EuI6 suffers from a high probability of self-absorption, which is almost completely absent in Cs4EuI6:2% Sm. Sm2+ doping is also used to gain insight in the migration rate of Eu2+ excitations in Cs4EuBr6 and Cs4EuI6, which shows that concentration quenching is weak, but still significant in the undoped compounds. Both self-absorption and concentration quenching are linked to the spectral overlap of the Eu2+ excitation and emission spectra which were studied between 10 K and 300 K. The scintillation characteristics of Cs4EuI6:2% Sm is compared to that of the undoped samples. An improvement of energy resolution from 11% to 7.5% is found upon doping Cs4EuI6 with 2% Sm and the scintillation decay time shortens from 4.8 s to 3.5 s in samples of around 3 mm in size
The role of Yb2+ as a scintillation sensitiser in the near-infrared scintillator CsBa2I5:Sm2+
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 0â1% 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 spinforbidden 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[2F7/2]5d1[LS] and 4f13[2F7/2]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
Charging mechanisms in persistent phosphors
The development of novel persistent phosphors is currently hampered by a limited understanding of the charging mechanism. Using x-ray absorption and thermoluminescence spectroscopy we evaluate the validity of recently proposed models for the charging mechanism
Light yield and thermal quenching of Ce3+ and Pr3+ co-doped LaBr3:Sm2+ near-infrared scintillators
LaBr3:Ce3+ is a compound with excellent scintillation properties, but its ultraviolet emission does not match
well with the detection efficiency curves of silicon based photodetectors. In this work, Sm2+ is studied as
an activator for LaBr3 as its near-infrared emission can be detected with close to 100% efficiency by such
photodetectors. LaBr3:Sm2+ single crystals were grown with and without co-doping of Ce3+ or Pr3+. The
samples were studied by means of X-ray excited and photoluminescence spectroscopy at temperatures between
10 K and 300 K. Their spectroscopic properties are compared to LaBr3:Ce3+ and LaBr3:Eu2+. The effect of using
Ce3+ or Pr3+ as scintillation sensitiser for Sm2+ is assessed. It is found that energy transfer from host to Sm2+
greatly improves upon Ce3+ co-doping, but the quenching temperature of the Sm2+ emission decreases. The
quenching mechanism of both the Ce3+ and Sm2+ emission in LaBr3 is elaborated on. Furthermore, the effect
of charge compensating defects on the light yield and spectroscopic properties is discussed
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Advanced Gamma-Ray Detection Concepts Combined with Real-Time Compton Suppression for Nondestructive, Gamma-Ray Characterization of Remote Handled Waste
Nondestructive gamma ray characterization of remote-handled waste is significantly complicated by the presence of Compton scattering in the detector and waste matrix produced by intense cesium gamma rays. This research seeks to understand the photophysics of a new type of inorganic scintillation gamma ray detector, optimize the combination of this gamma ray detector with a Compton guard detector, develop new Monte Carlo solution algorithms for modeling Compton scattering in the waste, and to model the real time intensity of cesium produced Compton scattering. A successful research program will provide the fundamental information needed to design and develop advanced Compton spectrometers for assay of remote handled waste and new higher sensitivity spectrometers for environmental measurements
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