Afterglow Level Research Articles

Scintillation properties of Er3+-activated BaO–Nb2O5–TeO2 glasses

Recently, glasses have gained great interest for use as scintillators owing to lots of industrial benefits such as ease of producing customizable shapes and low production cost. Herein, the Er3+-activated BaO–Nb2O5–TeO2 glasses were fabricated for the development of NIR glass scintillators. The Er3+-activated BaO–Nb2O5–TeO2 glasses exhibited efficient photoluminescence and scintillation that originated from the 4f→4f transition of Er3+. Their quantum yields in photoluminescence were 80% (0.1%Er2O3), 81% (0.5%Er2O3), and 61% (1.0%Er2O3). Further, an almost linear correlation between an X-ray dose rate and NIR scintillation intensity was observed in the 0.5–5000 mGy h−1 dose rate range. Interestingly, the lowest detectable dose rate limit (0.5 mGy h−1) was lower than that of Er-doped Bi4Ge3O12 and Nd-doped GdVO4 single crystals. Further, afterglow levels of the non-doped and Er3+-activated BaO–Nb2O5–TeO2 glasses were about 600 ppm. The observed NIR scintillation properties indicated that the Er3+-activated tellurite glasses should be promising compounds for NIR-emitting scintillators.

Scintillation properties of Pr-doped CaWO4 single crystals synthesized by the floating zone method

Pr-doped CaWO4 single crystals with dopant concentrations of 0.05–1% were synthesized by the floating zone method, and the photoluminescence and scintillation properties were evaluated. Emissions due to the 4f–4f transitions of Pr3+ were observed in visible–near-infrared ranges under visible light and X-ray irradiation. The X-ray-induced scintillation decay times were typical values of the transitions of Pr3+ when monitored at 380–900 nm. The afterglow levels when 20 ms passed after X-ray irradiation were calculated to be 573–730 ppm and increased as the dopant concentrations increased. In the integration-type scintillation detector property, 0.05, 0.1, and 0.5% Pr-doped samples showed good linearity between X-ray exposure dose rate and scintillation signals from 0.05 to 5 Gy/h.

The improved scintillation performances and X-ray imaging of Lu2O3:Pr3+ nanoparticles induced by Sm3+ doping

Lu2(1-x)Pr2xO3 nanoscintillators (x = 0.0005, 0.001, 0.0015, 0.003, 0.005) with excellent red emission and a response time of 185.7 μs were synthesized by a coprecipitation method. It is found that both photoluminescence and radioluminescence intensities show an initial rising and then decreasing trend with increasing Pr3+ concentration and the strongest intensity can be obtained at x = 0.001. By determining the average distance between Pr and O, the radiative transition processes from 3P0 and 1D2 to 3H4 and nonradiative transition process from 3P0 to 1D2 can be confirmed. Meanwhile, the afterglow level of Lu2O3:Pr3+ nanoscintillators with an average size of 112.3 nm was found to be 2190 ppm. Based on the spectral data and density functional theory calculations, the afterglow can be related to PrLu· traps due to the presence of Pr4+ in Lu2O3:Pr. When Sm3+ ions were doped into Lu2O3:Pr3+, it is found that it leads to the decreased creation of Pr4+, the reduced afterglow level and the improved radioluminescence. By means of Lu2O3:Pr3+, Sm3+ nanoparticles being dispersed into polymethyl methacrylate (PMMA) polymer, PMMA-Lu2O3:Pr3+, Sm3+ composite films with fast response time and radiation resistance were prepared by a rotating coating method. The static X-ray imaging with a spatial resolution of 5.5 lp/mm using the composite film as an imaging screen was realized at extremely low safe dose of 4.6 μGy. Meanwhile, for the broken electric wire used as an object, the clear X-ray image can be observed. Our results suggest that Lu2O3:Pr3+, Sm3+ nanoscintillators have potential applications in medical imaging and nondestructive testing.

Enhancement of Scintillation Properties of LYSO:Ce Crystals by Al Codoping

Single-crystal lutetium yttrium oxyorthosilicate doped by cerium (LYSO:Ce) has been widely adopted as a scintillator material for radiation detection. The demands from nuclear medical imaging, as well as high-energy physics, are calling for ever-increasing scintillation properties. Here, Al3+ codoping of LYSO:Ce is realized for the first time, and a series of LYSO:Ce,xAl (x = 0, 0.3, 0.6, and 1.0 atom %) crystals are successfully grown by a micro-pulling down (μ-PD) method. It is found that at x = 0.6 atom %, the overall scintillation properties are simultaneously improved. In particular, the slow component of rise time and the afterglow level are drastically reduced by 350% (from 304 to 86 ps) and an order of magnitude (from 0.2 to 0.02%), respectively. The energy resolution is also enhanced from 16.1 to 10.9%. These results are attributed to the fact that Al3+ codoping significantly reduces the concentration of traps, accelerates the excited state lifetime of Ce3+ ions and introduces a faster scintillating luminescence center, Ce4+ ions. Our LYSO:Ce,0.6 atom % Al crystal offers a gain in the image signal-to-noise ratio of 1.4 over the non-codoped crystal, which will significantly benefit the next-generation time-of-flight positron emission tomography and enable more precise diagnosis of diseases.

Visible–Near Infrared Scintillation Properties of Er-Doped Bi4Si3O12 Single Crystals

We synthesized the 0.5, 1.0, 2.0, and 3.0% Er-doped Bi4Si3O12 (BSO) single crystals and researched the photoluminescence (PL) and scintillation properties in visible–near infrared ranges. The X-ray diffraction analysis indicated that the synthesized samples had single-phase structure of BSO. In transmission spectra, all the samples had some absorption peaks owing to the 4f-4f transitions of Er3+ ions. In PL and scintillation properties, all the samples had the emission peaks due to the 6p-6s transitions of Bi3+ ions and the 4f-4f transitions of Er3+ ions. Afterglow levels at 20 ms after X-ray irradiation of the 0.5, 1.0, 2.0, and 3.0% Er-doped samples were 348.9, 587.9, 616.6, and 666.6 ppm, respectively. The light yields of the 0.5, 1.0, 2.0, and 3.0% Er-doped samples were 1600, 1200, 900, and 750 ± 10% ph/MeV, respectively. The dose rate response functions of all the samples showed the linear relationship between dose rate and scintillation intensity from 0.006 to 6 Gy h−1, and the 2.0% Er-doped sample had the highest intensity among the samples

Photoluminescence and scintillation properties of organic-inorganic layered perovskite-type compounds (FC6H4C2H4NH3)2PbCl4 crystals

(C6H5C2H4NH3)2PbCl4 and (n-FC6H4C2H4NH3)2PbCl4 (n = 2, 3, and 4) crystals were grown by the slow-cooling method, and the optical and scintillation properties were investigated. From the X-ray diffraction pattern, F-substitution in a benzene ring makes the lattice constant larger than (C6H5C2H4NH3)2PbCl4. They exhibited photoluminescence and scintillation peaks due to the recombination of the self-trapped excitons confined in inorganic layers at 400–700 nm. The afterglow levels at 20 ms after X-ray irradiation for 2 ms were 100–600 ppm. From the pulse height spectra under 241Am α-ray (5.5 MeV) irradiation, the light yields of (C6H5C2H4NH3)2PbCl4, (3-FC6H4C2H4NH3)2PbCl4, and (4-FC6H4C2H4NH3)2PbCl4 samples were calculated to be 1,400, 1,800, and 1,700 ph/5.5 MeV-α.

Evaluation of scintillation properties of Mg4(Ta,Nb)2O9 single crystals

Mg4(Ta,Nb)2O9 single crystals were synthesized by the floating zone method, and the photoluminescence and scintillation properties were evaluated. Under X-ray irradiation, Mg4Ta2O9 single crystal showed an emission peak at 350 nm, while Nb-contained ones showed an emission peak at 400 nm. The decay curves were approximated by one exponential decay function, which indicated the decay time in μs order. Among the samples, Mg4Ta1.5Nb0.5O9 showed the highest light yield of 22,000 ph/MeV and the lowest afterglow levels of ∼10 ppm.

X-ray-Induced Scintillation Properties of Nd-Doped Bi4Si3O12 Crystals in Visible and Near-Infrared Regions.

Undoped, 0.5, 1.0, and 2.0% Nd-doped Bi4Si3O12 (BSO) crystals were synthesized by the floating zone method. Regarding photoluminescence (PL) properties, all samples had emission peaks due to the 6p-6s transitions of Bi3+ ions. In addition, the Nd-doped samples had emission peaks due to the 4f-4f transitions of Nd3+ ions as well. The PL quantum yield of the 0.5, 1.0, and 2.0% Nd-doped samples in the near-infrared range were 67.9, 73.0, and 56.6%, respectively. Regarding X-ray-induced scintillation properties, all samples showed emission properties similar to PL. Afterglow levels at 20 ms after X-ray irradiation of the undoped, 0.5, 1.0, and 2.0% Nd-doped samples were 192.3, 205.9, 228.2, and 315.4 ppm, respectively. Dose rate response functions had good linearity from 0.006 to 60 Gy/h for the 1.0% Nd-doped BSO sample and from 0.03 to 60 Gy/h for the other samples.

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.

Ce concentration dependence on scintillation properties of SrHfO3 single crystals

Transparent and yellowish Ce-doped SrHfO3 (Ce:SHO) single crystals were grown by the xenon lamp equipped floating zone method. The synthesized crystals were in the single phase of SHO crystal structure, and no impurity phases such as HfO2 were evident by the X-ray diffraction analysis. The Ce:SHO shows blue luminescence peaking at 410 nm in both the PL and scintillation spectra, and the decay time constant was approximately 14 ns. The PL QY increases with the Ce concentration, which was confirmed up to 5%. The afterglow level is the lowest when the Ce concentration is 3%. The full energy peak can be demonstrated with all the Ce:SHO single crystals prepared in this study under 241Am alpha-ray irradiation, and the estimated light yield is 396 photons/MeV for the 3% Ce:SHO, which is the highest among the samples studied.

Influence of calcium doping concentration on the performance of Ce,Ca:LuAG scintillation ceramics

Ce,Ca:LuAG scintillation ceramics with different Ca2+ co-doping concentrations were prepared by the solid-state reaction method. The concentration of Ce3+ was fixed at 0.3 at% and the concentration of Ca2+ ranged from 0 to 1.2 at%. We systematically studied how the Ca2+ concentration affects the optical quality of Ce,Ca:LuAG ceramics by influencing the microstructure in the vacuum sintering and HIP post-treatment. Good optical transmittance could be obtained with Ca2+ concentrations between 0.05 and 0.8 at%, which reached 76.0–81.9 % at 520 nm. The PL and scintillation decay times decrease with increasing Ca2+ concentration up to 0.6 at% with no clear trend above this value. The light yield (LY) values at different shaping times decrease with increasing Ca2+ concentration but the fast scintillation component (LY0.5 μs/ LY3.0 μs) increases significantly from 79 % to 97 %. The co-doping of Ca2+ also reduces the afterglow level by more than one order of magnitude.

Scintillation characteristics of Eu2O3-doped WO3–Al2O3–TeO2 glasses

Eu2O3-doped tellurite glasses (15WO3–5Al2O3–80TeO2) were fabricated and their scintillation characteristics were investigated. Typical emissions originating from the 4f→4f transitions of Eu3+ were observed at 580, 592, 614, 653, and 702 nm when irradiated with visible light. The quantum yield of the Eu2O3-doped glass increased as the Eu2O3 concentration increased, and the 5.0% Eu2O3-doped glass exhibited the largest quantum yield of 76%. Further, scintillation originating from the 4f→4f transition of Eu3+ was also detected under X-ray irradiation, and the integrated scintillation intensity depended on the quantum yield. The afterglow levels of the glasses decreased with increasing the Eu2O3 concentration, and the level of the 5.0% Eu2O3-doped glass was 193 ppm, which was close to that of the Tl-doped CsI.

Ce concentration dependence on scintillation properties of Ce-doped yttrium pyrosilicate single crystal

Yttrium pyrosilicate (Y2Si2O7) single crystals are successfully grown by the floating-zone method with 0.5–10.0% of Ce-doping concentration. X-ray diffraction patterns indicate a single phase of Y2Si2O7 without the impurity phase. The series photoluminescence (PL) and scintillation properties are systematically explored in this study, including PL emission, PL decay time, X-ray induced scintillation spectra, X-ray induced scintillation decay time, afterglow profile, and pulse height spectra. Ce-doped Y2Si2O7 is presented interesting properties including the intense emission band at 390 nm from Ce3+ 5d-4f transition on both PL emission contour maps as well as X-ray-induced scintillation spectra in all samples. The afterglow level at 20 ms after X-ray irradiation of the Ce-doped YPS is comparable with commercial scintillators such as CdWO4 and Tl-doped CsI. Under 137Cs (662 keV) γ-ray irradiation 137Cs (662 keV), the highest scintillation light yield of Ce-doped Y2Si2O7 is reach up to 17,200 ph/MeV for 2.0% Ce-doped sample.

Scintillation Properties of Pr-Doped Lanthanum Pyrosilicate Single Crystals

Five samples of lanthanum pyrosilicate (La2Si2O7) single crystals with 0.5–10.0% Praseodymium (Pr)-doping concentrations were synthesized by the floating-zone method. Photoluminescence and scintillation properties of these crystals were investigated in this study for the first time. The multiple emissions from electron transitions of Pr3+ were observed on both a photoluminescence emission map and scintillation spectra, including the desired emission band of Pr3+ 5d–4f transition at 250–310 nm. The major photoluminescence and scintillation decay times were approximately 19 and 26 ns, respectively. When compared with commercial scintillators such as Tl-doped cesium iodide (CsI), the Pr-doped La2Si2O7 samples presented a respectively low afterglow level of 32 ppm after 20 ms of X-ray irradiation. Under 662 keV γ-ray irradiation from 137Cs, the 3.0% Pr-doped La2Si2O7 sample presented a scintillation light yield of 3200 ph/MeV, which was the best value among the tested samples.

Effects of two strategies on afterglow behavior of Lu2O3:Eu single crystal scintillator: Co-doping with Pr3+ and solid solution with Sc2O3

In this paper, effect of two strategies on afterglow behavior of Lu2O3:Eu single crystal scintillator, Pr3+ co-doping and solid solution with Sc2O3, were studied systematically. Two groups of Lu2O3:5 at%Eu,x at%Pr (x = 0, 0.2, 0.5, 1, 2 and 5) and (Lu1–yScy)2O3:5 at%Eu (y = 0, 20 at%, 50 at% and 70 at%) single crystals were grown by floating zone (FZ) method in air atmosphere. The structures of as-grown crystals were determined by X-ray diffraction (XRD). The scintillation, photoluminescence properties and carrier trap states were investigated through afterglow, X-ray excitation luminescence (XEL), transmittance, photoluminescence excitation (PLE) and photoluminescence (PL), PL decay and thermal stimulated luminescence (TSL) curves. It is found that with the increase of Pr3+ concentration, the afterglow level of the system decreases at the expense of scintillation luminescence efficiency. Meanwhile, although Sc2O3:Eu presents much lower afterglow intensity than Lu2O3:Eu, the addition of Sc2O3 will just increase the afterglow level of the (Lu1–yScy)2O3:5 at%Eu single crystal system. Possible mechanisms for above phenomena are discussed based on experimental results.

Ce concentration dependence of optical and scintillation properties on Ce-doped La2Si2O7 crystal

A lanthanum pyrosilicate (La2Si2O7, LaPS) single crystal is successfully grown with a Ce-doped concentration of 0.5 to 20.0% as well as undoped LaPS for reference. The photoluminescence emission map of Ce-doped LaPS has broad emission at 360–410 nm from Ce3+ 5d-4f transition, with a decay time of 20–24 ns. In the scintillation properties, Ce-doped LaPS presents the scintillation peak at 390 nm under X-ray excitation, with the decay time constant at 26–31 ns plus another decay constant caused by the emission from host material at 250–600 ns. The afterglow level at 20 ms after X-ray irradiation is around 30–56 ppm. In the 662 keV γ-ray pulse height spectra, 1.0% Ce-doped LaPS shows a clear photoabsorption peak, with a scintillation light yield of 5400 ph MeV−1. The relationship between γ-ray energy and the photoabsorption peak channel (linearity) is also covered in this study.

Scintillation characteristics of Nd3+-doped BaO–Al2O3–TeO2 glasses

Photoluminescence and scintillation characteristics of Nd3+-doped TeO2 glasses [(15–x)BaO–5Al2O3–80TeO2–xNd2O3 (x = 0.1–1.0)] were evaluated. The Nd3+-doped TeO2 glasses exhibited sharp emission peaks originating from the 4f–4f transition of Nd3+ in photoluminescence. The 0.1% Nd3+-doped TeO2 glass showed the highest quantum yield (about 33%). In addition, 0.1%–1.0% Nd3+-doped TeO2 glasses showed photoluminescence decay time constants in the time range of 128–194 μs originating from the 4F3/2 → 4I9/2 transition of Nd3+. In scintillation, the 0.1%–1.0% Nd3+-doped TeO2 glasses exhibited sharp scintillation peaks at around 905, 1060, and 1335 nm ascribed to the 4f–4f transitions of Nd3+. The 0.5% and 1.0% Nd3+-doped TeO2 glasses exhibited high intensities. The decay times of the Nd3+-doped TeO2 glasses under X-ray were in the time range of 123–174 μs. Moreover, the Nd3+-doped TeO2 glasses exhibited afterglow levels of about 618–829 ppm.

Concentration and temperature dependence behaviors of photoluminescence and scintillation properties of Lu2O3:Pr single crystals

Praseodymium doped lutecia (Lu1−xPrx)2O3 (x = 0.003, 0.006 and 0.01) single crystals have been prepared by optical floating zone (OFZ) method. The concentration and temperature dependence of photoluminescence and scintillation properties, including photoluminescence excitation (PLE) and photoluminescence (PL), PL decay, X-ray excited luminescence (XEL) and afterglow curves were systematically investigated. Both onward (Pr(S6)→Pr(C2)) and inverse (Pr(C2)→Pr(S6)) energy transfers are observed in Lu2O3:Pr. It is found that with the increasing of Pr3+ concentration, the Pr(S6)→Pr(C2) energy transfers efficiency increases. And the PL decay time becomes faster due to the increasing cross relaxation transition. Meanwhile, as the temperature increases (78–500 K), the onward and inverse energy transfer efficiencies between the two kinds of Pr3+ are enhanced simultaneously. The highest scintillation efficiency is Lu2O3:0.6%Pr and afterglow levels of obtained single crystals were comparable.

Investigation of Er:Bi4Ge3O12 single crystals emitting near-infrared luminescence for scintillation detectors

0.1%, 0.5%, and 1% Er:Bi4Ge3O12 (BGO) single crystals were grown by the floating zone method, and the structural, optical, and scintillation properties were investigated. From the X-ray diffraction analyses, all the obtained crystals were confirmed to be in the single phase of BGO. The crystals exhibited photoluminescence and scintillation due to the 4f–4f transitions of Er3+ peaking at ~550 and 1540 nm as well as an emission band due to the 3P1–1S0 transitions of Bi3+ across 400–600 nm. The photoluminescence quantum yields of the NIR emission (1429–1677 nm) were 50.6%, 85.8%, and 69.0% for the 0.1%, 0.5%, and 1% Er-doped crystals, respectively. The scintillation decay curves were measured in the spectral range from UV to NIR, and the decay time constants of the visible–NIR luminescence were confirmed to be consistent with the known values of Er3+. The afterglow level at 20 ms after X-ray irradiation was 12.0–25.4 ppm, which is similar to the value of Nd:BGO. All the crystals showed a good linearity between the near-infrared luminescence intensity and X-ray exposure dose rate, and the lowest detectable dose rate was 0.006 Gy/h in all the crystals.

Radiation response properties of Eu3+-doped K2O–Ta2O5–Ga2O3 glasses

Eu2O3-doped 40K2O–20Ta2O5–40Ga2O3 gallate glasses were synthesized, and their radiation response characteristics were studied systematically. According to their photoluminescence spectra, they showed intense emissions with sharp peaks centered at around 580, 594, 613, 656, and 706 nm when irradiated by 380 nm light. The sharp peaks originate from the 4f-4f transitions of Eu3+. Moreover, these sharp peaks were also detected when excited by X-ray, and the 1.0% Eu2O3-doped gallate glasses showed the largest luminescence intensity under UV light and X-ray. Furthermore, the afterglow levels of the Eu2O3-doped 40K2O–20Ta2O5–40Ga2O3 gallate glasses were determined to be approximately 300 ppm. These levels are close to the levels of TI-doped CsI single crystals.