Luminescent properties of CsI single crystals grown from the melt treated with EuI2

CsI single crystals treated with EuI₂ as a scavenger are grown and their radioluminescence spectra and scintillation light decay curves are obtained. Addition of the quantities of the scavenger comparable with the total concentration of the oxygen‐containing admixtures in the melt results in complete destruction of the latter. In its turn, this causes the disappearance of the band with a maximum at 2.8 eV in the radioluminescence spectrum and decreases the fraction of the slow 2 µs‐component to 0.01. The addition of larger quantities of EuI₂ leads to the appearance of a wide band with the maximum at 2.8 eV characterized by a decay constant of 2 µs; its intensity increases with the EuI₂ concentration. The maximum ratio of two faster components with the decay constants equal to 7 and 30 ns approaches 0.58:0.41 at EuI₂ concentration in CsI melt equal to 0.01 mol·kg⁻¹.     

Thermally stimulated luminescence of polycrystalline CdWO4 at low temperatures

CdWO₄ scintillator powders were produced via solid state reaction and investigated by thermally stimulated luminescence technique after UV irradiation. Under a heating rate of 0.1 K/s, the glow curve presented a superposition of peaks at low temperatures. Four peaks were identified below 80 K by partial heating method and their kinetic parameters were evaluated from the initial rise analysis. Measurements were also performed for heating rates of 0.05 and 0.2 K/s and allowed the kinetic study by peak position method. Surface effects due to the polycrystalline feature of the sample were investigated by comparing the results with those reported for CdWO₄ single crystals.     

Photo- and radio-excited luminescence properties of Eu-doped La2O3–Al2O3 based eutectics

Eutectic crystal of 0.5% Eu-doped 30LaAlO₃–70Al₂O₃ (vol %) was prepared by micro-pulling down (μ-PD) technique under nitrogen atmosphere. Being excited at a wavelength of 320 nm, the crystal exhibited intense emission band with a maximum at 450 nm which is corresponding to 4f⁶5d-4f⁷(⁸S_7/2) transitions of Eu²⁺. The decay time and fluorescence quantum efficiency (QE) were determined to be about 475 ns and 60%, respectively. When alpha-ray excited the crystal, both Eu²⁺ 4f⁶5d-4f⁷(⁸S_7/2) and Eu³⁺ 4f⁶-4f⁶ (⁵D₀-⁷F_1,2) emission peaks were observed at 435 nm and 600 nm. By the pulse height spectra, the relative scintillation light yield of the crystal was about 4% compared with that of BGO commercial scintillator.     

Energy transfer and annealing behavior of luminescence in Dy-doped PbWO4 single crystal

The Dy³⁺: PWO single crystal was subsequently annealed in air atmosphere at a temperature of 500°C, 550°C, 600°C, 700°C, 800°C, 900°C, and 1000°C, respectively. X-ray excited luminescence spectra were measured before and after each step of annealing. Annealing experiments confirmed the energy transfer-taking place from PbWO₄ (PWO) host to Dy³⁺ ions, followed by the enhancing characteristic emission of Dy³⁺ ions. In the process of annealing, the luminescence of PWO host was significantly reduced while that of Dy³⁺ was increased simultaneously. Annealing at a temperature below 700°C suppressed the blue luminescence of the PWO host and enhanced its green components, while the emission of Dy³⁺ is increased to some extent. Further annealing at higher temperature strongly reduced the luminescence of the PWO host, while the emission of Dy³⁺ was greatly increased. Interstitial oxygen O_i could play an important role in the luminescence. Annealing could modify the luminescence of Dy³⁺ ions in PWO, which may be useful in terms of some application purposes.     

Scintillation properties of Zr co-doped Ce:(Gd,La)2Si2O7 grown by the Czochralski process

(Gd_0.75,Ce_0.015,La_0.235)₂Si₂O₇ (Ce:La-GPS) single crystals co-doped with 0, 100, 200, 500 and 1000 ppm Zr were grown by the Czochralski process, and their scintillation properties were investigated. We investigated the co-doping effect of a stable tetravalent ion in Ce:La-GPS for the first time. The scintillation decay times in the faster component were shortened with increasing the Zr concentration. While the non-co-doped sample showed ∼63 ns day time, the Zr 100, 200, 500 and 1000 ppm co-doped samples showed ∼61, ∼59, ∼57, ∼54 ns, respectively. Additionally, light output, photon nonproportional response (PNR) and other optical properties were investigated.     

Potential of GAGG:Ce scintillation crystals for synchrotron X-Ray micro-imaging

We examined the use of cerium-doped gadolinium aluminum gallium garnet (GAGG:Ce) as a material for scintillation screens in synchrotron X-ray radiography (SXR). Highlighted for gamma-ray detection, GAGG:Ce is also an attractive material for SXR because of its high X-ray stopping power and the high light yield at around 530?nm. A thin and transparent screen prepared from our grown ingot of GAGG:Ce was compared with commonly used scintillators of CdWO₄ and YAG:Ce in terms of image quality under monochromatic X-ray illumination. Micron spatial resolutions were achieved with comparable image quality, suggesting that a single crystal of GAGG:Ce is competent scintillation material for SXR.     

Ion implantation of zinc sulphide

The passivation of argon sputter-etch induced electrically active defects on Ge, Si, and GaAs surfaces by reaction with atomic hydrogen has been observed using deep level transient spectroscopy. A broad band of defect states, giving rise to non-linear Arrhenius plots, appears to be associated with the induced damage centres. For n-type Ge and p-type Si, a 20-min exposure to atomic hydrogen at 180°C is shown to neutralize the damage created by a 5-min, 6 kV (DC), Ar gas sputter-etch. For n-type GaAs a 1-h exposure at 250°C was sufficient, whilst n-type Si required a 1-h exposure to the hydrogen plasma at 300°C to passivate the damage. In each case, to remove the sputter-etch damage by thermal annealing required temperatures approximately 100°C higher, for periods of approximately 2 h.     

Scintillation properties of Yb-doped garnet crystals

Luminescence properties of heavily Yb-doped Lu₃Al₅O₁₂ (Yb:LuAG) and Lu₃Ga₅O₁₂ (Yb:LGG) single crystals grown by micro-pulling-down method were characterized. Charge transfer luminescence of Yb³⁺ was observed in both crystals. Photoluminescence spectra, temperature dependence of emission intensity and decay kinetics of these crystals were studied. Mean decay time of about 24 ns at 90 K (Yb5%:LuAG) and 21 ns at 110 K (Yb5%:LuGG) were observed. Strong thermal quenching at room temperature was measured for both Yb:LuAG and Yb:LGG.     

Changes in trap parameters in various mixed oxide garnets

Shallow and deep electronic traps in various mixed oxide garnet ceramics (Y,Lu,Gd)₃(Al,Ga)₅O₁₂ have been studied by thermally stimulated luminescence spectroscopy in the 80–550 K temperature range. It is shown that the substitution of Al ions by Ga and Y by Gd or Lu in YAG:Ce affects the properties of the traps. It is established that the studied ceramics contain residual impurities of chromium and ytterbium. On the base of the obtained and literature data, a table of the Cr-related trap position relative to the bottom of the conduction band in RE₃(Ga_x,Al_5-x)₅O₁₂:Ce garnets (RE = Lu, Y, Gd and combinations thereof) has been constructed.     

Fiber-coupled Al2O3:C radioluminescence dosimetry for total body irradiations

In vivo dosimetry can be important and relevant in radiotherapy, especially when commissioning new treatment techniques at hospitals. This study investigates the potential use of fiber-coupled radioluminescence (RL) dosimetry based on Al₂O₃:C or organic plastic scintillators for this purpose in the context of Total Body Irradiations (TBIs) where patients are treated with large fields of 6 or 18 MV photons at an extended source-to-surface distance (SSD). The study shows that Al₂O₃:C dosimetry using the saturated-RL protocol may be suitable for real-time in vivo dosimetry during TBI treatments from the perspective of the good agreement with alanine dosimetry and other critical phantom tests, including the ability to cope with the large stem signal experienced during TBI treatments at extended SSD. In contrast, the chromatic stem removal technique often used for organic plastic scintillators did not work well in large fields with the tested calibration procedure and instrumentation. An apparent dose-rate effect discussed in a previous study of the RL properties of Al₂O₃:C (Andersen et al., 2011) was found to have resulted from an overlooked dead time problem in the counting system, and this potential caveat can therefore be removed from the list of potential problems associated with fiber-coupled Al₂O₃:C dosimetry using the saturated-RL protocol. This further has implications for TBI dosimetry using the RL Al₂O₃:C system due to large dose-rate differences between calibrations at the iso-center and in vivo measurements at extended source-to-surface distances.