Decrease Of Light Yield Research Articles

Temperature dependence of photoluminescence kinetics and scintillation properties of LuY2(Al5-xScx)O12:Ce (x = 1, 1.5, 2) garnet single-crystalline films

The temperature dependence of photoluminescence (PL) kinetics and scintillation properties were investigated in LuY2(Al5-xScx)O12:Ce (x = 1, 1.5, 2) garnet single-crystalline films grown by the isothermal liquid phase epitaxy method. With the increase of Sc content, the Ce3+ 5d1 level was shifted to higher energy while the Ce3+ 5d2 level was shifted to lower energy due to the decrease in crystal field splitting of the 5d levels. Activation energy of thermal quenching, determined from temperature-dependent PL decay times, decreased with increasing Sc content. At room temperature, the decrease of light yield (LY) value with increasing Sc content is caused by the thermal ionization process. LuY2(Al4Sc)O12:Ce showed a LY value of 510 photons/MeV when excited by 5.5 MeV α-particles, which is ∼21 % larger than that of Lu2Y(Al4Sc)O12:Ce due to a smaller bandgap Eg of the former.

Effect of Dual-Organic Cations on the Structure and Properties of 2D Hybrid Perovskites as Scintillators.

Two-dimensional (2D) hybrid organic-inorganic perovskite (HOIP) crystals show promise as scintillating materials for wide-energy radiation detection, outperforming their three-dimensional counterparts. In this study, we synthesized single crystals of (PEA2-xBZAx)PbBr4 (x ranging from 0.1 to 2), utilizing phenethylammonium (C6H5CH2CH2NH3+) and benzylammonium (C6H5CH2NH3+) cations. These materials exhibit favorable optical and scintillation properties, rendering them suitable for high light yield (LY) and fast-response scintillators. Our investigation, employing various techniques such as X-ray diffraction (XRD), photoluminescence (PL), time-resolved (TR) PL, Raman spectroscopy, radioluminescence (RL), thermoluminescence (TL), and scintillation measurements, unveiled lattice strain induced by dual-organic cations in powder X-ray diffraction. Density functional theory analysis demonstrated a maximal 0.13 eV increase in the band gap with the addition of BZA cation addition. Notably, the largest Stokes shift of 0.06 eV was observed in (BZA)2PbBr4. The dual-organic cation crystals displayed >80% fast component scintillation decay time, which is advantageous for the scintillating process. Furthermore, we observed a dual-organic cations-induced enhancement of electron-hole transfer efficiency by up to 60%, with a contribution of >70% to the fast component of scintillation decay. The crystal with the lowest BZA concentration, (PEA1.9BZA0.1)PbBr4, demonstrated the highest LYs of 14.9 ± 1.5 ph/keV at room temperature. Despite a 55-70% decrease in LY for BZA concentrations >5%, simultaneous reductions in scintillation decay time (12-32%) may work for time-of-flight positron emission tomography and photon-counting computed tomography. Our work underscores the crucial role of dual-organic cations in advancing our understanding of 2D-HOIP crystals for materials science and radiation detection applications.

Optical and scintillation characteristics of Lu2Y(Al5-xGax)O12:Ce,Mg multicomponent garnet crystals

Optical and scintillation characteristics of Mg2+-codoped Lu2Y(Al5-xGax)O12:Ce (x = 2, 3) multicomponent garnet crystals grown by the micro-pulling down method were investigated. At RT, the shortening of scintillation decay time and a decrease of light yield (LY) value measured for a higher Ga containing samples can be explained by thermal ionization of the Ce3+ 5d1 excited state. At 662 keV γ-rays, Lu2YAl3Ga2O12: Ce, 0.05%Mg exhibits high LY value of 29,000 ph/MeV along with scintillation decay times of 50 ns (86%) + 73 ns (14%). Co-doping with larger Mg2+ content leads to a decrease of LY value, scintillation decay time, and afterglow level. Radioluminescence quenching observed at low temperature region in correlation with large thermoluminescence peaks can be caused by trapping of electrons at intrinsic shallow traps.

Temperature effects on light yield and pulse shape discrimination capability of siloxane based scintillators

In this work, we report the study of temperature effects on light yield of siloxane-based scintillators and on n/gamma discrimination capability, in terms of pulse shape discrimination (PSD). The solid scintillators are composed of phenyl containing polysiloxane (PMPS100), as a base polymer, loaded with moderate amounts (6 wt%) of 2,5-diphenyloxazole (PPO) as a primary dye and Lumogen Violet (LV) as waveshifter. The samples were heated in the range of 60–150 ^circ hbox {C} and scintillation performance were tested both after annealing for 24 h and in real time during heating. Light yield of siloxane-based scintillators containing 6 wt% PPO heated at 100 ^circ hbox {C} is very close to the room-temperature value, while heating at 120 ^circ hbox {C} causes a decrease of light yield (LY) of 17%. In addition, the figure of merit (FoM) for n/gamma discrimination of the scintillator shows a sensible worsening of the discrimination performances in case of prolonged treatment at 120 ^circ hbox {C}. Similar tests are made using the commercial plastic scintillator EJ-299 (currently named EJ-276), based on polyvinyltoluene (PVT). In this case, the light yield undergoes a much more rapid deterioration with annealing temperature, and at 70 ^circ hbox {C} it is reduced to 60% of the original value. The discrimination capability of EJ-299 decreases upon heating at 70 ^circ hbox {C} as well, with a 20% reduction of FoM; meanwhile for T > 70 ^circ hbox {C} the mechanical and optical features are remarkably degraded. The mass loss of primary dye PPO from the siloxane scintillator as a function of treatment temperature and initial dye concentration has been evaluated and compared to the behaviour of EJ-299. This measurement allows to single out and characterize a series of processes occurring during heating, which are relevant to the whole performance of the system under study, such as sublimation at the interface, thermally induced photooxidation of components, diffusion of fluorophores from the polymer bulk to the surface. The variation in luminescence characteristics have been analyzed by excitation/fluorescence spectroscopy and time-resolved fluorescence spectroscopy, in order to correlate the annealing treatment with the primary dye loss by sublimation, formation of superficial aggregates and/or degradation of the scintillator components in the synthesized siloxane scintillator.

Optics robustness of the ATLAS Tile Calorimeter

TileCal, the central hadronic calorimeter of the ATLAS detector is composed of plastic scintillators interleaved by steel plates, and wavelength shifting optical fibres. The optical properties of these components are known to suffer from natural ageing and degrade due to exposure to radiation. The calorimeter was designed for 10 years of LHC operating at the design luminosity of 1034 cm−2s−1. Irradiation tests of scintillators and fibres have shown that their light yield decrease by about 10% for the maximum dose expected after 10 years of LHC operation. The robustness of the TileCal optics components is evaluated using the calibration systems of the calorimeter: Cs-137 gamma source, laser light, and integrated photomultiplier signals of particles from proton-proton collisions. It is observed that the loss of light yield increases with exposure to radiation as expected. The decrease in the light yield during the years 2015-2017 corresponding to the LHC Run 2 will be reported. The current LHC operation plan foresees a second high luminosity LHC (HL-LHC) phase extending the experiment lifetime for 10 years more. The results obtained in Run 2 indicate that following the light yield response of TileCal is an essential step for predicting the calorimeter performance in future runs. Preliminary studies attempt to extrapolate these measurements to the HL-LHC running conditions.

High-Z Sensitized Plastic Scintillators: A Review.

The need for affordable and reliable radiation detectors has prompted significant investment in new radiation detector materials, due to concerns about national security and nuclear nonproliferation. Plastic scintillators provide an affordable approach to large volume detectors, yet their performance for high-energy gamma radiation is severely limited by the small radiation stopping power inherent to their low atomic number. Although some sensitization attempts with organometallics were made in the 1950s to 1960s, the concomitant decrease in light yield has limited the usefulness of these sensitized detectors. Recently, with new knowledge gained during the rapid development of organic optoelectronics and nanotechnology, there has been a revived interest in the field of heavy element sensitized plastic scintillators. Here, the recent efforts on sensitized plastic scintillators are summarized. Basic scintillator physics is first reviewed. The discussion then focuses on two major thrusts in the field: sensitization with: (1) organometallics and (2) oxide and fluoride nanoparticles. The design rationales and major results are examined in detail, with existing limitations and possible future pathways discussed. Special attention is paid to the underlying energy deposition and transfer processes, as these determine the key performance metrics such as light yield and radioluminescence decay lifetime.

Improvement and luminescent mechanism of Bi4Si3O12 scintillation crystals by Dy3+ doping

Bi4Si3O12:Dy (BSO:Dy) crystals have been grown by the modified vertical Bridgeman method and doping effects on light yield have been investigated. Doped with small amount of Dy2O3 (0.05–0.3mol%), the light yield and energy resolution of BSO crystals were improved significantly. However, high concentrations of Dy2O3 doping resulted in the decrease of light yield. Pulse height measurement under γ-ray irradiation shows that 0.1mol% Dy2O3 doping can make the relative light yield of BSO from 24.6% to 35.8% of BGO crystal, with fast decay time of ~90ns. X-ray excited radioluminescence spectra showed Dy doping has an extra emission in the host emission band (Bi3+ emission) and acts as a sensitizer to the Bi luminescent center. These results indicate that BSO:Dy crystal could be one of promising candidates for replacing BGO in some application such as electromagnetic calorimeter and dual readout in nuclear or high energy physics.

Scintillation properties of Ca co-doped L(Y)SO:Ce between 193 K and 373 K for TOF-PET/MRI.

Time-of-flight Positron Emission Tomography (TOF-PET) and TOF-PET/MRI require scintillators with high light yield, short decay time, and short rise time in order to obtain high timing resolution. LSO:Ce and LYSO:Ce are commonly used. Ca co-doped LSO:Ce shows improved scintillation properties. The decay time constant of LSO:Ce,0.2%Ca (~33 ns) is shorter than standard LSO:Ce (~38-40 ns), and it has about 15% higher light yield. We measured scintillation pulse shapes and photoelectron yields of LSO:Ce, LSO:Ce,0.2%Ca, LYSO:Ce, LYSO:Ce,20ppmCa, LYSO:0.11%Ce,0.2%Mg, and LYSO:0.2%Ce,0.2%Ca at temperatures ranging from 193 K to 373 K. To study rise times we built a set-up in which samples are excited by 100 ps (FWHM) x-ray pulses. Figure ​Figure11 shows that the scintillation rise time of LSO:Ce,0.2%Ca is constant between 273 K and 373 K, while the decay time constant decreases. Figure ​Figure22 shows that the light yield of LSO:Ce,0.2%Ca decreases with rising temperature. We noticed that the decrease in light yield is entirely caused by non-radiative decay of excited Ce3+ centres. This quenching mechanism does not worsen the timing resolution, as opposed to recombination of electron-hole pairs. It follows that the timing resolution of LSO:Ce(,0.2%Ca) is constant over the entire temperature range, in accordance with the timing model described in [1]. Figure 1 Scintillation pulse shape of LSO:Ce,0.2%Ca. Figure 2 Normalized scintillation properties as a function of temperature.

Effects of Bi3+ codoping on the optical and scintillation properties of CsI:Tl single crystals

CsI:Tl single crystals with different Bi3+ concentrations from zero to 0.05 mol% were grown by the vertical Bridgman technique. The effects of Bi3+ codoping on the scintillation properties of CsI:Tl single crystals were investigated, including afterglow level, relative light yield, energy resolution, scintillation decay time and radioluminescence spectra. Afterglow suppression by Bi3+ codoping was confirmed, but it resulted in a considerable decrease of light yield and energy resolution. The deterioration of light yield was ascribed to the self-absorption effect induced by Bi3+ ions. The physical mechanism and role of Bi3+ ions in afterglow suppression were proposed.

Effect of the Pr3+ → Gd3+ energy transfer in multicomponent garnet single crystal scintillators

Luminescence processes in the undoped and Pr3+-doped (Gd,RE)3(Ga,Al)5O12, RE = Lu,Y, multicomponent garnets are studied by time-resolved photoluminescence spectroscopy. Energy transfer processes between Pr3+ and Gd3+ causing significant deterioration of the scintillation performance are considered in detail. As is shown in current work, an overlap of the 5d1–3H4 emission transition of Pr3+ and 8S–6Px absorption transition of Gd3+ results in unwanted depletion of Pr3+ 5d1 excited state and is further intensified by the concentration quenching in the Gd3+-sublattice. This process explains a drastic decrease of light yield in Pr3+-doped Gd3+-containing multicomponent garnets observed in a previous work.

Study of radiation hardness of Gd2SiO5 scintillator for heavy ion beam

Gd2SiO5 (GSO) scintillator has very excellent radiation resistance, a fast decay time and a large light yield. Because of these features, GSO scintillator is a suitable material for high radiation environment experiments such as those encountered at high energy accelerators. The radiation hardness of GSO has been measured with Carbon ion beams at the Heavy Ion Medical Accelerator in Chiba (HIMAC). During two nights of irradiation the GSO received a total radiation dose of 7 × 105 Gy and no decrease of light yield was observed. On the other hand an increase of light yield by 25% was observed. The increase is proportional to the total dose, increasing at a rate of 0.025%/Gy and saturating at around 1 kGy. Recovery to the initial light yield was also observed during the day between two nights of radiation exposure. The recovery was observed to have a slow exponential time constant of approximately 1.5 × 104 seconds together with a faster component. In case of the LHCf experiment, a very forward region experiment on LHC (pseudo-rapidity η > 8.4), the irradiation dose is expected to be approximately 100 Gy for 10 nb−1 of data taking at (s)1/2 = 14TeV. The expected increase in light yield of less than a few percent will not affect the LHCf measurement.

Luminescence of heavily Ce-doped alkaline-earth fluorides

The spectral and kinetic parameters of M 1− x Ce x F 2+ x ( x=0.35, M=Ca, Sr, Ba) crystals luminescence have been studied. These characteristics are compared to the luminescence of solution base hosts: MF 2:Ce and CeF 3. The emission bands of heavily Ce-doped alkali earth fluorides are closed to the spectrum of perturbed Ce-center in CeF 3 at T=9 K. Luminescence of M 0.65Ce 0.35F 2.35 crystals reveals the efficient excitation in the UV and VUV ranges. The main feature of the emission and excitation spectra of Ce 3+ luminescence is the displacement to the low-energy range according to the bandgap decrease in the Ca-, Sr- and Ba-based fluorides, respectively. Small Stokes shift leads to the reabsorption and light yield decrease. Luminescence peculiarities of M 1− x Ce x F 2+ x solid solution and the role of Ce-enriched inclusions are discussed.

Ecofriendly liquid phase oxidation with hydrogen peroxide of 2,6-dimethylphenol to 2,6-dimethyl-1,4-benzoquinone catalyzed by TiO 2–CeO 2 mixed xerogels

Titania–ceria mixed xerogels were prepared with 10% (w/w) CeO 2 and different pH values during the sol–gel process. The gels were dried in air and calcined at different temperature. Moreover, a sample without cerium, 100% (w/w) TiO 2, was prepared to be kept as reference material. The prepared solids were characterized by means of XRD, SEM, DRS, FT-IR, TEM and EDX. Their textural properties were determined by adsorption–desorption isotherms of N 2 at 77 K. The xerogels were tested as catalysts in the liquid phase oxidation of 2,6-dimethylphenol at 20 °C, using ethanol as solvent and aqueous hydrogen peroxide as a clean oxidizing agent. The 2,6-dimethyl- p-benzoquinone yield achieved was of 85–96% using the mixed xerogels as catalysts, and of 49% when the catalyst of titania without cerium was used. The best performance was achieved by the mixed xerogel synthesized at pH 4 and calcined at 200 °C; 100% of conversion of 2,6-dimethylphenol and 96% of yield in 2,6-dimethyl- p-benzoquinone were obtained in this case after 6 h of reaction. The reactions were again carried out with the catalyst recovered after its first use. Only a light yield decrease, lower than 2%, was observed. The use of an ethanol–water mixture as solvent (35:65% (v/v)) in the reaction was studied in order to make the reaction more environmentally friendly. Total conversion of the initial reactant, after 4 h of reaction at 20 °C, with 70% yield in 2,6-dimethyl- p-benzoquinone (2,6-DMBQ), was observed. Under these conditions a red by-product, insoluble in the reaction solution, was formed. This by-product was isolated and characterized and it was possible to identify it as 2,6-DMBQ dimmer (3,3′,5,5′-tetramethyl-4,4′-diphenoquinone). This by-product was observed in very few amounts when ethanol (96% (v/v)) was used as solvent.

Growth, thermo-stability and radiation damage of cerium-doped lanthanum chloride (LaCl 3:Ce) scintillation crystal

LaCl 3:5%Ce crystals with diameter of 25 mm were grown by modified non-vacuum Bridgman method. Their photo-luminescence at temperature from 80 to 500 K in steps of 50 K were measured by the single-photon counting method with FLS920 spectrofluorimeter. It was found that the total emission intensity above room temperature is little stronger than that below room temperature. And the decay times also show slight increase with temperature. Irradiation with γ-ray from 60Co source will induce some optical absorption within 320–500 nm in the crystals, cause decrease of light yield and change the relative intensity ratio of the two emissions from 5d→ 2F 5/2 and 5d→ 2F 7/2, but have no influence on the luminescence mechanism.

Radiation tests of CsI(Tl) crystals for the GLAST satellite mission

The electromagnetic calorimeter of the Gamma-ray Large Area Space Telescope (GLAST) consists of 16 towers of CsI(Tl) crystals. Each tower contains 8 layers of crystals (each 326.0 × 26.7 × 19.9 mm 3 ) arranged in a hodoscopic fashion. The crystals are read out at both ends with PIN diodes. Crystals produced by Amcrys-H are used. As a part of the quality control procedure during crystal production, samples from the uncut boules were systematically irradiated with gamma-rays from a 60Co source. The decrease in light yield due to radiation damage was measured, determining the radiation hardness of the boule. All boule samples passed the radiation hardness requirements, showing an average decrease in light yield of (14 ± 4)% after having received a dose of 200 Gy. Studies have also been carried out to verify the correspondence between the post-irradiation properties of the boule samples and the full-size crystals which are subsequently cut from the boule. A crystal log was irradiated with gamma-rays from a 60Co source and showed a decrease in light yield of (24 ± 4)% after a dose of 180 Gy. A full-size crystal was also irradiated with a 180 MeV proton beam and the radiation induced attenuation and induced radioactivity was studied. The light yield was found to have decreased with (22 ± 5)% after 175 Gy, and the dominant radioactive isotopes were identified.

Mechanism of Scintillation of Helium, Helium-Argon, and Helium-Neon Gas Mixtures Excited by Alpha Particles

An experimental investigation of the mechanism of scintillation of helium, helium-argon, and helium-neon mixtures excited by $\ensuremath{\alpha}$ particles has been performed. No detectable decrease in light yield was observed at pressures less than 3 atm when the applied electric field was increased in steps to $\frac{E}{p}\ensuremath{\sim}1.0$ V/cm Torr, where $E$ is the electric field and $p$ is the gas pressure. The pulse shape of helium scintillation light consists of a slow component and a spike appearing on the leading edge of the pulse. The main component of light intensity is represented by the formula $\mathrm{exp}(\ensuremath{-}\frac{t}{{\ensuremath{\tau}}_{m}})\ensuremath{-}\mathrm{exp}(\ensuremath{-}\frac{t}{{\ensuremath{\tau}}_{f}})$, where $t$ is the time in sec, ${\ensuremath{\tau}}_{m}=10\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ sec, and ${\ensuremath{\tau}}_{f}=0.3{p}^{\ensuremath{-}2.2\ifmmode\pm\else\textpm\fi{}0.3}$ sec ($p$ in Torr). Most of the emitted photons had a wavelength of less than 1050 \AA{}A. On the basis of these results, it is concluded that the emitted photons are released in the decay of excited helium molecules formed as a result of a three-body collision between a metastable and two ground-state helium atoms. A characteristic large drop in the light yield for a mixture of a small proportion of argon in a major fraction of helium can be explained by the production of argon ions by metastable helium atoms (Penning process). The same characteristic large drop for a mixture of small concentration of neon in helium seems to be caused by the excitation transfer from helium to neon atoms. The cross section ${\ensuremath{\sigma}}_{f}$ for the formation of an excited helium molecule by a three-body collision is estimated to be $50\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}23}p$ ${\mathrm{cm}}^{2}$ at 300\ifmmode^\circ\else\textdegree\fi{}K, where $p$ is in Torr. From the value of ${\ensuremath{\sigma}}_{f}$, the cross section ${\ensuremath{\sigma}}_{i}$ of the helium-argon Penning process is calculated as 41\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ and 14\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ by using the ratios of ${\ensuremath{\sigma}}_{i}$ to ${\ensuremath{\sigma}}_{f}$ estimated by Jesse and Sadauskis and by Northrop and Gursky, respectively.