Scintillation Decay Kinetics Research Articles

Three-Layered Composite Scintillator Based on the Epitaxial Structures of YAG and LuAG Garnets Doped with Ce3+ and Sc3+ Impurities.

In this study, we propose novel three-layer composite scintillators designed for the simultaneous detection of different ionizing radiation components. These scintillators are based on epitaxial structures of LuAG and YAG garnets, doped with Ce3+ and Sc3+ ions. Samples of these composite scintillators, containing YAG:Ce and LuAG:Ce single crystalline films with different thicknesses and LuAG:Sc single crystal substrates, were grown using the liquid phase epitaxy method from melt solutions based on PbO-B2O3 fluxes. The scintillation properties of the proposed composites, YAG:Ce film/LuAG:Sc film/LuAG:Ce crystal and YAG:Ce film/LuAG:Ce film/LuAG:Sc crystal, were investigated under excitation by radiation with α-particles from a 239Pu source, β-particles from 90Sr sources and γ-rays from a 137Cs source. Considering the properties of the mentioned composite scintillators, special attention was paid to the ability of simultaneous separation of the different components of mixed ionizing radiation containing the mentioned particles and quanta using scintillation decay kinetics. The differences in scintillation decay curves under α- and β-particle and γ-ray excitations were characterized using figure of merit (FOM) values at various scintillation decay intensity levels (1/e, 0.1, 0.05, 0.01).

Scintillation properties of Cs4Mg3F10 crystal grown by micro-pulling-down method

In our search for cross-luminescence (CL) scintillators suitable for fast-timing applications, we have chosen CsMgF3 as one of the perspective candidates. During the attempts to grow CsMgF3 by the micro-pulling-down method, we have revealed the presence of Cs4Mg3F10 which is in contradiction with the published equilibrium phase diagram. The Cs4Mg3F10 has an orthorhombic structure, consisting of face-sharing MgF6 octahedra triplets (4 triplets per unit cell), joined to 4 other triplets by corner sharing. These chain-like structures are separated by Cs+ ions. Moreover, Cs4Mg3F10 is non-hygroscopic despite the hygroscopic nature of CsF. The best crystals were grown from CsF-rich melt to suppress off-stoichiometry due to CsF evaporation during crystal growth. Both radioluminescence spectra and scintillation decay kinetics exhibit complex character and the presence of CL in Cs4Mg3F10 is still under question. However, due to relatively low scintillation efficiency and the presence of slow components in scintillation decay, Cs4Mg3F10 is not suitable for fast-timing applications.

The Ga-admixed GSAG:Ce single crystal scintillator: Composition tuning

The scintillation, luminescence and optical properties of the multicomponent Gd3Sc2Ga(2+x)Al(1-x)O12:Ce (x = 0, 0.25, 0.5, 0.75, 1), Gd2.957Sc1.905Ga(2.138+x)Al(1-x)O12:Ce (x = 0, 1) and the (200, 1000, 5000 ppm) Mg2+ co-doped Gd3Sc2Ga2.75Al0.25O12:Ce single crystals grown by the μ-PD method were characterized. Scintillation decay kinetics and light yield were correlated with the sum of the content of Ga and Sc in the host. While the Ga-admixed GSAG:Ce composition exhibited higher scintillation efficiency compared to pure GSAG:Ce, it also showed very high afterglow, due to an intense delayed electron-hole recombination at Ce3+ centres. This was supported by the calculated activation energy obtained from the temperature dependence of photoluminescence decay times. Codoping with Mg2+ significantly improved afterglow compared to pure GSAG:Ce, however, at the expense of light yield.

Segregation effects of Tl and Li ions on the scintillation properties of NaI:Tl,Li single crystals

In this work, high quality NaI:Tl and NaI:Tl,Li single crystals with a size of 11 mm in diameter and 135 mm in length were grown by the multi-ampoule Bridgman method. The concentrations of Tl and Li ions along the solidification direction were measured by the inductively coupled plasma optical emission spectrometer. The effective segregation coefficients of Tl and Li in NaI single crystals were estimated as 0.26 and 0.35, respectively. The radioluminescence spectra under X-ray excitation, pulse height spectra and scintillation decay kinetics under γ-ray excitation of the samples taken from different solidification positions in NaI:Tl and NaI:Tl,Li single crystals were systematically studied. For RL spectrum and scintillation decay time, there is a negligible position-dependent difference for both NaI:Tl and NaI:Tl,Li single crystals. In contrast, the energy resolution at 662 keV gradually deteriorates along the solidification direction, and the light yield maintains almost the same until reaching the last-to-freeze region.

Single Crystalline Films of Ce3+-Doped Y3MgxSiyAl5-x-yO12 Garnets: Crystallization, Optical, and Photocurrent Properties.

This research focuses on LPE growth, and the examination of the optical and photovoltaic properties of single crystalline film (SCF) phosphors based on Ce3+-doped Y3MgxSiyAl5-x-yO12 garnets with Mg and Si contents in x = 0-0.345 and y = 0-0.31 ranges. The absorbance, luminescence, scintillation, and photocurrent properties of Y3MgxSiyAl5-x-yO12:Ce SCFs were examined in comparison with Y3Al5O12:Ce (YAG:Ce) counterpart. Especially prepared YAG:Ce SCFs with a low (x, y < 0.1) concentration of Mg2+ and Mg2+-Si4+ codopants also showed a photocurrent that increased with rising Mg2+ and Si4+ concentrations. Mg2+ excess was systematically present in as-grown Y3MgxSiyAl5-x-yO12:Ce SCFs. The as-grown SCFs of these garnets under the excitation of α-particles had a low light yield (LY) and a fast scintillation response with a decay time in the ns range due to producing the Ce4+ ions as compensators for the Mg2+ excess. The Ce4+ dopant recharged to the Ce3+ state after SCF annealing at T > 1000 °C in a reducing atmosphere (95%N2 + 5%H2). Annealed SCF samples exhibited an LY of around 42% and similar scintillation decay kinetics to those of the YAG:Ce SCF counterpart. The photoluminescence studies of Y3MgxSiyAl5-x-yO12:Ce SCFs provide evidence for Ce3+ multicenter formation and the presence of an energy transfer between various Ce3+ multicenters. The Ce3+ multicenters possessed variable crystal field strengths in the nonequivalent dodecahedral sites of the garnet host due to the substitution of the octahedral positions by Mg2+ and the tetrahedral positions by Si4+. In comparison with YAG:Ce SCF, the Ce3+ luminescence spectra of Y3MgxSiyAl5-x-yO12:Ce SCFs greatly expanded in the red region. Using these beneficial trends of changes in the optical and photocurrent properties of Y3MgxSiyAl5-x-yO12:Ce garnets as a result of Mg2+ and Si4+ alloying, a new generation of SCF converters for white LEDs, photovoltaics, and scintillators could be developed.

Scintillation properties of (Lu1-x Y x )3Al5O12:Ce3+ nanoscintillator solid solution garnet materials

In this study, the scintillation properties of the (Lu1-x Y x )3Al5O12: 0.1 at.%Ce3+ mixed nanopowder scintillators synthesized by the sol-gel method were investigated. The light yield, energy resolution and scintillation decay kinetics for different substitutions of Lu3+ by Y3+ ion, namely 0 at.%, 5 at.%, 10 at.%, 15 at.% and 20 at.% were evaluated. The relative light yields of all LuYAG mixed samples were determined by the comparison method and the LuAG:0.1 at.%Ce3+ single crystal grown by the Czochralski technique was used as a reference detector. The scintillation decay kinetics was measured at the photomultiplier tube anode output and a fast digital oscilloscope was used to digitize signals. All measurements were performed under α-particles excitation from 241Am (E = 5.48 MeV) source to avoid light scattering in powder materials. Results show that the scintillation light yield was affected by the insertion of Y3+ ions in the LuAG host matrix and tends to improve in the range 10–20 at.% of Y3+ content. Furthermore, it was found that the main contribution in the energy resolution originates from the nanoscintillator material. The scintillation decay curves were well-fitted to a sum of three exponential functions, and the decay time constants were determined. Additionally, pulse shape discrimination of the mixed LuYAG nanoscintillators was also checked, and good discrimination of the kinetics measured under α-particles and γ-quanta from 137Cs (E = 662 keV) was observed.

New types of composite scintillators based on the single crystalline films and crystals of Gd3Al5-xGaxO12:Ce garnets

This work presents the results on creation of novel types of composite scintillators based on Ce3+ doped Gd3Al5-xGaxO12 single crystalline films grown by the LPE method using PbO–B2O3 flux onto substrate-scintillators prepared from commercial Gd3Al2.3Ga2.7O12:Ce and Gd3Al2Ga3O12:Ce single crystals. The sets of films with different Ga contents x = 1.75–2.25 and various thicknesses in the 13–150 μm range were grown onto the mentioned substrates. The scintillation properties of the respective epitaxial structures (pulse height spectra, light yield and scintillation decay kinetics) were investigated under excitation by α– (239Pu) particles, β- (90Sr+90Y) particles and γ–quanta (137Cs). The best scintillation properties for simultaneous registration of the mentioned particles and quanta in the mixed radiation fluxes are demonstrated with Gd3Al2.75Ga2.25O12 film/Gd3Al2Ga3O12:Ce substrate epitaxial structure.

Optical properties of epitaxially grown GaN:Ge thin films

To better understand the scintillation properties of gallium nitride, a detailed characterization of Metal Organic Vapour Phase Epitaxy (MOVPE) grown GaN layers doped with Ge is conducted. This study includes the measurements of radioluminescence and photoluminescence spectra, thermally stimulated luminescence as well as scintillation decay kinetics. The representative radio- and photoluminescence spectra are composed of two bands. The narrow and fast band peaking at about 3.4 eV is ascribed to excitons and the broad and slow defect-related band with the maximum at about 2.2 eV is produced by carbon occupying nitrogen site. It has been found that the decay kinetics and amplitude of the exciton and defect emission are sensitive to the Ge doping level. In particular, the exciton- and the defect-related luminescence become faster with increasing Ge content. Charge trapping processes were also affected by the Ge doping.

The influence of Si on the properties of MOVPE grown GaN thin films: Optical and EPR study

Metal Organic Vapour Phase epitaxy (MOVPE) grown GaN layers doped with Si were studied by means of radio-, photo- and thermally stimulated luminescence, scintillation decay kinetics, as well as electron paramagnetic resonance. Two luminescence bands were observed: the narrow and fast peaking at about 3.45 eV (ascribed to excitons) and the broad and slow one having maximum at about 2.2 eV (produced by the defect – a carbon occupying nitrogen site). The decay time and the intensity of exciton and defect-related emission exhibit dependence on the doping level of Si. Both bands are getting faster upon the increased Si content. Moreover, the presence of Si influences drastically the charge trapping processes as well – the changes in the intensity of the glow peaks within the 100–300 K temperature range were observed. Besides, the new glow peaks appear and are getting stronger in the 300–450 K region upon Si doping. Interestingly, the effect of Si on the conductivity properties of the GaN samples was observed by means of electron paramagnetic resonance.

Gd-admixed (Lu,Gd)AlO3 single crystals: breakthrough in heavy perovskite scintillators

We report a breakthrough concept for a bulk single crystal as a heavy aluminum perovskite scintillator, where due to bandgap engineering by a balanced Gd admixture in a Lu cation sublattice, the scintillation performance dramatically increases. In an optimized composition of (Lu, Gd)AlO3:Ce (LuGdAP:Ce), the light yield approaches 21,000 phot/MeV, which is close to that of classical but much less dense YAP:Ce and 50% higher than the best LuYAP:Ce reported in the literature. Moreover, contrary to LuYAP:Ce, the LuGdAP host maintains a high effective atomic number close to that of LuAP:Ce (Zeff = 64.9), which is comparable to commercial LSO:Ce. An enormous decrease in afterglow on the millisecond time scale and acceleration in the rise time of the scintillation response further increase the application potential of the LuGdAP host. The related acceleration of the transfer stage in the scintillation mechanism due to diminishing electron trap depths is proven by thermally stimulated luminescence (TSL). Furthermore, we quantitatively characterize and model the energy transfer processes that are responsible for the change in the photoluminescence and scintillation decay kinetics of Ce3+ in the LuGdAP matrix. Such an innovative (Lu, Gd)AP:Ce scintillator will become competitive for use in applications that require heavy, fast, and high light yield bulk scintillators.

Development of Composite Scintillators Based on the LuAG: Pr Single Crystalline Films and LuAG:Sc Single Crystals

The scintillation properties of novel type of composite scintillator based on Lu3Al5O12:Pr (LuAG:Pr) single crystalline film (SCF) and LuAG:Sc substrate grown by the liquid-phase epitaxy method are considered in this work. The registration of α-particles and γ-quanta in such types of composites occurs by means of separation of the scintillation decay kinetics of SCF and crystal parts, respectively. Namely, under excitation by α-particles of 241Am (5.5 MeV) source and γ-quanta of 137Cs (662 keV) source, the large differences in the respective scintillation decay kinetics and decay time values tα and tγ are observed for the LuAG:Pr SCF/LuAG:Sc SC composite scintillator with various film thicknesses. Furthermore, the best tγ/tα ratio above 4.5 is achieved for such types of epitaxial structure with SCF and substrate thicknesses of 17 μm and about 0.5 mm, respectively. The development types of composite scintillators can be successfully applied for simultaneous registration of α-particles and γ-quanta in the mixed radiation fluxes.

Crystallization and Investigation of the Structural and Optical Properties of Ce3+-Doped Y3−xCaxAl5−ySiyO12 Single Crystalline Film Phosphors

This work is devoted to the crystallization and investigation of the optical properties of single crystalline films (SCFs) of Ce3+-doped Y3−xCaxAl5−ySiyO12 garnet, where the content of Ca2+ and Si4+ cations varied in the x = 0.13–0.52 and y = 0.065–0.5 ranges, respectively. The SCF samples were grown using the liquid phase epitaxy technique onto Y3Al5O12 substrates from the melt solution with equimolar Ca and Si content using PbO-B2O3 flux. However, the Ca and Si concentration in Y3−xCax Al5−ySiyO12:Ce SCFs is not equal: the Ca2+ content was systematically larger than that of Si4+, and the Ca2+ excess is compensated for by the Ce4+ ion formation. The absorption, scintillation, and luminescent properties of Y3−xCaxAl5−ySiyO12:Ce SCFs with different Ca/Si concentrations were investigated and compared with the sample of YAG:Ce SCF. Due to the creation of Ce4+ ions, the as-grown Y3−xCaxAl5−ySiyO12:Ce SCFs show relatively low light yield (LY) under α–particle excitation but a fast scintillation response with a decay time in the ns range. After SCF annealing in the reducing (N2 + H2) atmosphere at T &gt; 1000 °C, the recharging of Ce4+→Ce3+ ions occurs. Furthermore, the samples annealed at 1300 °C SCF possess an LY of about 40% in comparison with the reference YAG:Ce SCF and scintillation decay kinetics much closer to that of the SCF counterpart. Due to Ca2+ and Si4+ alloying, the Ce3+ emission spectra in Y3−xCaxAl5−ySiyO12 SCFs are extended to the red range in comparison with the spectra of YAG:Ce SCF. Such an extension is caused by the Ce3+ multicenter formation at the substitutions of both Y3+ and Ca2+ dodecahedral positions in the hosts of these mixed garnets.

Composite Scintillators Based on the Films and Crystals of (Lu,Gd,La)2Si2O7 Pyrosilicates

This article is directed on the creation of composite scintillators which are based on the films and crystals of R2Si2O7:Ce (R = Lu, Gd, La) pyrosilicates using the liquid phase epitaxy (LPE) growth method for application in the radiation monitoring of different components of mixed ionization fluxes. Such types of composite scintillators are epitaxial structures containing film scintillators grown by the LPE method onto the substrates of crystal scintillators. In this article, the film and crystal parts of the composite scintillators were fabricated from effective scintillation materials on the base of Ce3+ doped Gd2- x Lu x Si2O7 and Gd2- x La x Si2O7, and $x = {0}$ and 0.25 mixed pyrosilicates with various scintillation decay kinetics due to the different Lu/Gd/La cation content. We briefly report on the results of the LPE growth of the composite scintillators based on the Ce3+ doped (Lu,Gd)2Si2O7 films and (Gd,La)2Si2O7:Ce crystal substrates, as well as the results of investigation of their luminescent and scintillation properties.

Liquid phase epitaxy growth of high-performance composite scintillators based on single crystalline films and crystals of LuAG

Top – Scheme of the composite scintillator for registration of α-particles and γ-quanta. Bottom – Samples of the LuAG:Ce SCF/LuAG:Sc SC (a) and LuAG:Pr SCF/LuAG:Sc SC (b) composite scintillators prepared using the liquid phase epitaxy growth method.

Novel All-Solid-State Composite Scintillators Based on the Epitaxial Structures of LuAG Garnet Doped With Pr, Sc, and Ce Ions

This paper presents our achievement in the development of new types of advanced composite scintillators (CSs) based on the single crystalline films (SCFs) of Lu3Al5O12 (LuAG) garnet, doped with Pr3+ and Sc3+ ions, and substrate from single crystals (SCs) of Ce3+-doped LuAG using the technology of liquid phase epitaxy. We show the possibility of the simultaneous registration of $\alpha$ -particles and $\gamma$ -quanta by means of separation of the decay kinetics of SCF and crystal parts of such CSs. Namely, the significant differences in the scintillation decay kinetics of LuAG:Pr SCF/LuAG:Ce SC and LuAG:Sc SCF/LuAG:Ce SC CSs under excitation by $\alpha$ -particles of 241Am (5.5 MeV) source and $\gamma$ -quanta of 137Cs (662 keV) source are observed. Thus, such types of CSs can be successfully applied for separation of the signals coming from their film and crystal parts at the registration of the mixed radiation fluxes of $\alpha$ -particles and $\gamma$ -quanta.

Composite scintillators based on the crystals and single crystalline films of LuAG garnet doped with Ce3+, Pr3+ and Sc3+ ions

This work is devoted to the development of new types of advanced composite scintillators based on the single crystalline films (SCFs) of Lu3Al5O12 (LuAG) garnet, doped with Pr3+ and Sc3+ ions, and substrate from single crystals (SCs) of Ce3+ doped LuAG using the technology of liquid phase epitaxy (LPE). We show the possibility of the simultaneous registration of α-particles and γ-quanta by means of separation of the decay kinetics of SCF and crystal parts of such composite scintillators. Namely, the significant differences in the pulse height spectra and the scintillation decay kinetics of LuAG:Pr SCF/LuAG:Ce SC and LuAG:Sc SCF/LuAG:Ce SC composite scintillators under excitation by α–particles of 241Am (5.5 MeV) source and γ-quanta of 137Cs (662 keV) source are observed. For these reasons, such types of composite scintillators can be applied for separation of the signals coming from their film and crystal parts at the registration of the mixed radiation fluxes of α-particles and γ-quanta.

Development of Composite Scintillators Based on Single Crystalline Films and Crystals of Ce3+-Doped (Lu,Gd)3(Al,Ga)5O12 Mixed Garnet Compounds

The possibility of growth by the liquid phase epitaxy method of a new type of advanced composite scintillator based on Ce3+-doped single crystalline films (SCFs) of Lu1.5Gd1.5Al1.5Ga3.5O12 garnet and substrates from single crystals (SCs) of Gd3Al2.5Ga2.5O12:Ce garnet is evidenced for the first time in this work. We show the possibility of the simultaneous registration of α-particles and γ-quanta by way of separation of the scintillation pulse height spectra and decay kinetics of SCF and crystal parts of such a composite scintillator. Namely, the significant differences in the scintillation decay kinetics of Lu1.5Gd1.5Al1.5Ga3.5O12:Ce SCF/Gd3Al2.5Ga2.5O12:Ce SC composite scintillator under excitation by α-particles of a 241Am (5.5 MeV) source and γ-quanta of 137Cs (662 keV) source are observed. The respective tα/tγ decay times ratio in the 0–500 ns range reach up to 0.5 for this type of composite scintillator; e.g., the SCF scintillators is two times faster than the substrate scintillator. For this reason,...

Scintillation response of Ce3+ doped GdGa-LuAG multicomponent garnet films under e-beam excitation

Scintillation properties of multicomponent (GdLuY)3(GaAl)5O12:Ce3+ epitaxial garnet films were studied under electron beam excitation. The role of the shallow traps was investigated using the scintillation decay kinetics and cathodoluminescence spectroscopy. Tunneling-driven recombination, which provides a physical ground for the slow scintillation decay component in LuAG:Ce single crystals, is discussed in detail.

X-ray detection capability of a Cs2ZnCl4 single-crystal scintillator

The X-ray detection capability of a scintillation detector equipped with a Cs2ZnCl4 single crystal was evaluated. The scintillation decay kinetics can be expressed as the sum of two exponential decay components. The fast decay component had a decay time constant of 1.8 ns, and its relative intensity was 95%. The total light output was 630 photons/MeV, and a subnanosecond timing resolution of 0.66 ns was obtained. The detection efficiency of 67.4 keV X-rays was 80% for a detector equipped with a 2.2-mm-thick Cs2ZnCl4 crystal. Thus, excellent timing resolution and high detection efficiency were achieved simultaneously.

X-ray detection capability of a BaCl2 single crystal scintillator

The x-ray detection capability of a scintillation detector equipped with a BaCl2 single crystal was evaluated. The scintillation decay kinetics can be expressed by a sum of two exponential decay components. The fast and slow components have lifetimes of 1.5 and 85 ns, respectively. The total light output is 5% that of YAP:Ce. A subnanosecond timing resolution was obtained. The detection efficiency of a 67.41 keV x-ray is 87% for a detector equipped with a BaCl2 crystal 6-mm thick. Thus, excellent timing resolution and high detection efficiency can be simultaneously achieved. Additionally, luminescence decay characteristics under vacuum ultraviolet excitation have been investigated. Radiative decay of self-trapped excitons is thought to be responsible for the fast scintillation component.