Pulsed X-ray Excitation Research Articles

Fast response 4f15d1→4f2 emission and host-to-impurity energy transfer in Pr3+ doped Na3LuSi3O9 double salt silicate

Understanding of host-to-impurity energy transfer process is crucial for the development of efficient and fast response scintillator materials. In this work, Pr3+ doped Na3LuSi3O9 (NLS) double salt silicate has been successfully synthesized using a high temperature solid-state reaction method and further comprehensively characterized by means of XRD measurements, crystal structure refinement, luminescence spectroscopic and time-domain study upon VUV-UV and X-ray synchrotron excitation, and thermally stimulated luminescence (TSL) study. Based on these results a model of host to Pr3+ 4f15d1 and 4f2 has been proposed. It has been demonstrated that NLS:Pr3+ has a good potential for fast response scintillator applications due to the presence of an efficient energy transfer from host electronic excitations to Pr3+ 4f15d1 states. The Pr3+ 4f15d1→4f2 emission reveals a good thermal stability and is characterized by a lifetime of about 16 ns. Upon pulse X-ray excitation the main fast decay component is accompanied by slower one with lifetime of about 64 ns that is ascribed to the presence of shallow traps which retrap carriers and cause appearance of delayed recombination. Parameters for the corresponding traps have been calculated based on the TSL glow curve analysis.

Time-resolved radioluminescence of the Cu(I) cluster Cu4I62-. Different responses to photo, X-ray, β-ray and α-particle excitation.

Time-resolved radioluminescence (TRRL) properties of the Cu(I) cluster Cu4I62- upon pulsed X-ray, β-ray or α-particle excitation are described. The longer (>2 μs) TRRL component displays exponential decay comparable to pulsed UV excitation; however, temporal behaviour at shorter times indicates that high local excited state density provides an alternative decay channel.

Optical and scintillation properties of Nd-doped Lu2Si2O7 single crystals

Lutetium pyrosilicate (Lu2Si2O7, LPS) single crystals were synthesized by the floating-zone method with different dopant concentration to investigate the Nd-concentration dependence on the photoluminescence (PL) and scintillation properties. The Nd-doped LPS presented PL peaking at 800–900 nm due to the 4–4f transitions with the PL quantum yield up to 34%. Under X-ray irradiation, the samples showed several sharp peaks in both UV–visible and NIR regions. The scintillation decay time constants were around 3–4 μs upon pulsed X-ray excitation, and the afterglow level at 20 ms after X-ray irradiation was 310–650 ppm. The scintillation light yields of the Nd-doped LPS under γ-rays from 137Cs were up to 800 ph/MeV. hMeV.

X-ray/proton and photoluminescence behaviors of Sm3+ doped high-density tungsten gadolinium borate scintillating glass

Sm-activated scintillating glasses with high WO3 concentration up to 42.5 mol% were studied in this work. The effects of Sm2O3 concentration on the density, absorption and various (photo-, X-ray induced-, proton- and temperature dependent-) luminescence properties have been monitored. The glasses possess a high density with maximum value around 6.18 g/cm3. The glass samples show the several absorption peaks of visible light and near-infrared wavelength those confirm the Sm3+ ion existence in glass matrices. The Gd3+→ Sm3+ energy transfer took place in glasses which resulted to the strongest emission around 600 nm (4G5/2 → 6H7/2) of Sm3+ in the photo-, X-ray induced- and proton luminescence spectra. The optimal doping concentration of Sm2O3 in WO3-Gd2O3˗B2O3 glass is 1.0 mol% that performed the highest emission intensity in these three types of luminescence spectra. In 1.0 mol% doped glass, the decay time under pulse X-ray excitation was analyzed and found to be 0.27 ms. The temperature dependent luminescence in a range of 10 K–300 K of 1.0 mol% doped glass was measured via UV-laser excitation. The emission intensity of glass increased 3.76 times with the temperature decrease. In this work, the fabricated WO3-Gd2O3˗B2O3 glasses doped with Sm2O3 show the strong visible luminescence under visible light, X-ray and proton excitation. The developed glass performs the potential for X-ray scintillator applications with integration mode using in the medical, industrial and security imaging inspection system.

Development of WO3-Gd2O3˗ B2O3 high density glasses doped with Dy3+ for photonics and scintillation materials application

The Dy3+ ions doped tungsten gadolinium borate (Dy-WGdB) glasses were synthesis by the melt-quenching technique with various Dy2O3 concentrations. The physics, optical and several types of luminescence properties in the Dy-WGdB glass samples were researched. Glass densities (~6.0 g/cm3) indicates that the compaction of glass is high and rise with an increment of Dy2O3 concentrations. The Dy-WGdB glass samples absorb photons in visible light (VIS) and near-infrared (NIR) region from the absorption spectra. For photo-, radio- and proton luminescence, the highest emission was observed at 575 nm, corresponding to Dy3+ transition 4F9/2 → 6H13/2. The maximum concentration of Dy2O3 doped in the WGdB glass is 1.0 mol%, which has achieved the highest emission intensity in all three types of luminescence. For 1.0 mol% doped glass, the decay times under pulse X-ray excitation was measured and found to be 0.216 ms. The temperature dependent luminescence spectra of the 1.0% doped glass in a temperature range, 10 K–300 K was measured and found the thermal quenching. In this research, under the photo, X-ray and proton excitation, the WGdB glass doped with Dy2O3 displays the strong luminescence in the VIS region. It has the potential for applications in high-energy and nuclear physics, radiation control and homeland security.

Scintillation detector properties of CsLiB6O10 (CLBO) crystal

CsLiB6O10 (CLBO) single crystal is one of the common nonlinear optical materials, and we open a new possibility of CLBO for ionizing radiation measurements. In photoluminescence (PL), an intense emission was observed at around 530 nm, and PL decay time was 535 ns. When X-ray induced scintillation spectrum was measured, an intense emission peak appeared at around 530 nm. The scintillation decay time upon pulsed X-ray excitation resulted 687 ns and 3.13 μs. The scintillation light yield of CLBO under 137Cs γ-ray irradiation was 64 000 ph MeV−1, and the energy resolution at 662 keV was 8 ± 0.3%.

Luminescence properties and host sensitization study of Ba3La(PO4)3:Ce3+ with (V)UV and X-ray excitation

We report on successful synthesis and comprehensive study of luminescence spectroscopic properties and decay kinetics of undoped and Ce3+-doped eulytite structure orthophosphate Ba3La(PO4)3 (BLP) upon excitation with UV-VUV and X-ray photons in a wide temperature range. An intrinsic emission located in the UV range is observed for undoped BLP upon both VUV and X-ray excitation. In turn, emission of Ce3+-doped BLP is represented by interconfigurational 5d-4f transitions arising from Ce3+ ions located in two crystallographic sites which demonstrate average decay time of 22 ns and 40 ns upon intracenter excitation. Pulse X-ray excitation results in appearance of slower (μs or longer) decay components and acceleration of the main 5d-4f emission decay component. Host sensitization of Ce3+ emission is well demonstrated by UV-VUV excitation spectra measurements both at liquid helium and at room temperature. Mechanisms influencing the efficiency and time scale of energy transfer from the host to Ce3+ dopant ions are analyzed and discussed while aiming to estimate the potentials of BLP:Ce3+ for scintillator and X-ray phosphor applications.

Mechanisms of luminescence decay in YAG-Ce,Mg fibers excited by γ- and X-rays

Time-resolved luminescence of YAG-Ce (150 ppm) fiber crystal with Mg co-doping was studied under pulsed X-ray excitation and γ-rays (Cs 662 keV). The initial part of decay kinetics under X-ray excitation is faster than for direct cerium excitation (63 ns). Decay kinetics is also characterized by the presence of slow components with at least two characteristic times longer than Ce3+ radiation time. The slowest one which dominates for t > 500 ns in YAG-Ce without Mg co-doping practically vanishes for samples with 50 ppm co-doping. Decay kinetics under γ-rays are characterized by slower rise time than that under X-rays. These properties can be explained by competition of energy transfer and energy losses in track regions. The distribution of excitations in tracks produced by X-rays differs from that in tracks produced by γ-rays, since the energy of primary electron after γ-quantum conversion is much higher than after X-ray absorption. The stopping power for energetic electrons decreases with increase of electron energy, and therefore the density distribution after X-ray conversion is shifted to higher densities, Therefore, the acceleration of recombination and quenching of excitations is more prominent under X-ray excitation. Specific role of Ce4+ induced by Mg co-doping is also discussed in the paper.

Megahertz non-contact luminescence decay time cryothermometry by means of ultrafast PbI2 scintillator

Realtime in situ temperature monitoring in difficult experimental conditions or inaccessible environments is critical for many applications. Non-contact luminescence decay time thermometry is often the method of choice for such applications due to a favorable combination of sensitivity, accuracy and robustness. In this work, we demonstrate the feasibility of an ultrafast PbI2 scintillator for temperature determination, using the time structure of X-ray radiation, produced by a synchrotron. The decay kinetics of the scintillations was measured over the 8–107 K temperature range using monochromatic pulsed X-ray excitation. It is found that lead iodide exhibits a very fast and intense scintillation response due to excitons and donor-acceptor pairs, with the fast decay component varying between 0.08 and 0.5 ns – a feature that can be readily exploited for temperature monitoring. The observed temperature dependence of the decay time is discussed in terms of two possible mechanisms of thermal quenching – transition over activation barrier and phonon-assisted escape. It is concluded that the latter provides a better fit to the experimental results and is consistent with the model of luminescence processes in PbI2. We evaluated the sensitivity and estimated the accuracy of the temperature determination as ca. ±6 K at 107 K, improving to ±1.4 K at 8 K. The results of this study prove the feasibility of temperature monitoring, using ultrafast scintillation of PbI2 excited by X-ray pulses from a synchrotron, thus enabling non-contact in-situ cryothermometry with megahertz sampling rate.

Effect of alkaline earth on decay time of Dy3+ doped in Li2O-B2O3 glasses using pulse X-ray excitation

Abstract Different types of alkaline earth lithium borate glasses doped with 0.5 mol% of Dy3+ ions in composition of 50Li2O:20MO:29.5B2O3:0.5Dy2O3 (where MO = MgO, CaO, SrO and BaO) were prepared by normal melts quenching technique. The as-prepared glasses were characterized by the density, the optical transmission spectra, and together with decay time under X-ray pulse excitation. With increasing of the molecular weight of alkaline earth oxides the density of glasses increased and the same trend has been observed for the molar volume. The transmission spectra in the wavelength region of 350-2500 nm showed the f - f excitations for Dy3+ ions from ground states 6H15/2 to other excited states 6F5/2, 6F7/2, 6F9/2, 6H7/2, (6F11/2, 6H9/2) and 6H11/2. Moreover, a large increase in decay time under pulse X-ray excitation with the larger size of alkaline earth cation have been observed.

Optimization of crystal growth and properties of γ-CuI ultrafast scintillator by the addition of LiI

Large-sized γ-CuI single crystals with ultrafast scintillation property were grown in LiI acetonitrile solvent through evaporation technique. The LiI exhibits unique properties to γ-CuI single crystal preparation. One is that it increases the solubility of CuI in the solvent, which gives rise to a largest-sized (23 × 14 × 2 mm3) single crystal with the high optical transmission (over 60%) in the wavelength region of 435–800 nm. The other feature is that it acts as an effective isoelectronic dopant and improves the molar ratio of copper to iodine, which greatly enhances the near-band-edge emissions (411 and 432 nm) and suppresses the broadband emission (680 nm). The decay time of the fast emission under pulsed X-ray excitation is shorter than 450 ps. The results will give a guidance for optimizing the properties of γ-CuI single crystal as an ultrafast scintillator.

Precise rise and decay time measurements of inorganic scintillators by means of X-ray and 511 keV excitation

The emergence of new solid-state avalanche photodetectors, e.g. SiPMs, with unprecedented timing capabilities opens new ways to profit from ultrafast and prompt photon emission in scintillators. In time of flight positron emission tomography (TOF-PET) and high energy timing detectors based on scintillators the ultimate coincidence time resolution (CTR) achievable is proportional to the square root of the scintillation rise time, decay time and the reciprocal light yield, CTR∝τrτd∕LY. Hence, the precise study of light emission in the very first tens of picoseconds is indispensable to understand time resolution limitations imposed by the scintillator. We developed a time correlated single photon counting setup having a Gaussian impulse response function (IRF) of 63ps sigma, allowing to precisely measure the scintillation rise time of various materials with 511keV excitation. In L(Y)SO:Ce we found two rise time components, the first below the resolution of our setup <10 ps and a second component being ∼380 ps. Co-doping with Ca2+ completely suppresses the slow rise component leading to a very fast initial scintillation emission with a rise time of <10ps. A very similar behavior is observed in LGSO:Ce crystals. The results are further confirmed by complementary measurements using a streak-camera system with pulsed X-ray excitation and additional 511 keV excited measurements of Mg2+ co-doped LuAG:Ce, YAG:Ce and GAGG:Ce samples.

Consequences of Ca Codoping in YAlO3 :Ce Single Crystals.

The influence of Ca codoping on the optical absorption, photo-, radio-, and thermo-luminescence properties of YAlO3 :Ce (YAP:Ce) crystals has been studied for four different calcium concentrations ranging from 0 to 500 ppm. Ca codoping results in a partial oxidation of Ce3+ into Ce4+ , The luminescence time response under pulsed X-ray excitation of the Ce3+ /Ce4+ admixure clearly demonstrates the role of hole migration on both the rise time and the generally observed slow components. From an application point of view, Ca codoping significantly improves the timing performances, but the induced presence of Ce4+ ions is also the cause of a reduction in scintillation efficiency.

X-ray excited luminescence of polystyrene composites loaded with SrF2 nanoparticles

The polystyrene film nanocomposites of 0.3mm thickness with embedded SrF2 nanoparticles up to 40wt% have been synthesized. The luminescent and kinetic properties of the polystyrene composites with embedded SrF2 nanoparticles upon the pulse X-ray excitation have been investigated. The luminescence intensity of the pure polystyrene scintillator film significantly increases when it is loaded with the inorganic SrF2 nanoparticles. The film nanocomposites show fast (∼2.8ns) and slow (∼700ns) luminescence decay components typical for a luminescence of polystyrene activators (p-Terphenyl and POPOP) and SrF2 nanoparticles, respectively. It is revealed that the fast decay luminescence component of the polystyrene composites is caused by the excitation of polystyrene by the photoelectrons escaped from the nanoparticles due to photoeffect, and the slow component is caused by reabsorption of the self-trapped exciton luminescence of SrF2 nanoparticles by polystyrene.

X-ray excited luminescence of polystyrene-based scintillator loaded with LaPO4–Pr nanoparticles

Polystyrene film nanocomposites of 0.3 mm thickness with embedded LaPO4-Pr nanoparticles (40 wt. %) have been synthesized. The luminescent and kinetic properties of these polystyrene composites with embedded LaPO4-Pr nanoparticles upon pulse X-ray excitation have been studied. The luminescence intensity of this polystyrene material significantly increases as it is loaded with inorganic LaPO4-Pr nanoparticles. Nanocomposite films reveal luminescence spectra typical for polystyrene activators (p-Terphenyl and POPOP) and two components of decay time kinetics of luminescence with 12 ns and 2.8 ns time constants, depending on nanoparticle sizes. The component with 12 ns decay constant arises due to the radiative transfer of the 5d-4f-emission of the Pr3+ ions in the LaPO4 nanoparticles to the polystyrene. The decay component with the time constant 2.8 ns originates from luminescence of polystyrene matrix excited by electrons emitted from nanoparticles due to the photoeffect. This nonradiative mechanism of energy transfer from nanoparticles to polystyrene matrices is determinative for nanoparticles, as their sizes are smaller than a mean free path of an electron.

Ultrafast emission from colloidal nanocrystals under pulsed X-ray excitation

Fast timing has emerged as a critical requirement for radiation detection in medical and high energy physics, motivating the search for scintillator materials with high light yield and fast time response. However, light emission rates from conventional scintillation mechanisms fundamentally limit the achievable time resolution, which is presently at least one order of magnitude slower than required for next-generation detectors. One solution to this challenge is to generate an intense prompt signal in response to ionizing radiation. In this paper, we present colloidal semiconductor nanocrystals (NCs) as promising prompt photon sources. We investigate two classes of NCs: two-dimensional CdSe nanoplatelets (NPLs) and spherical CdSe/CdS core/giant shell quantum dots (GS QDs). We demonstrate that the emission rates of these NCs under pulsed X-ray excitation are much faster than traditional mechanisms in bulk scintillators, i.e. 5d-4f transitions. CdSe NPLs have a sub-100 ps effective decay time of 77 ps and CdSe/CdS GS QDs exhibit a sub-ns value of 849 ps. Further, the respective CdSe NPL and CdSe/CdS GS QD X-ray excited photoluminescence have the emission characteristics of excitons (X) and multiexcitons (MX), with the MXs providing additional prospects for fast timing with substantially shorter lifetimes.

Scintillation Characteristics of Indium Doped Cesium Iodide Single Crystal

Indium doped cesium iodide (CsI:In) single crystals were grown by the Bridgman method. A comparison study of the scintillation properties of our CsI:In and commercially available CsI:Tl single crystals was carried out, including scintillation decay time, energy resolution, non-proportionality, absolute light yield, and afterglow. Under X-ray excitation, the CsI:In emission corresponds to a symmetrical broad band centered at 545 nm. Its scintillation decay time is <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$1.99 \pm 0.02~\mu\hbox{s}$</tex> </formula> at room temperature under <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{137}{\rm Cs}\gamma $</tex></formula> -ray excitation. The CsI:In light yield was found to be <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$34,700 \pm 1735$</tex></formula> photons per MeV with an energy resolution of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$9.1 \pm 0.3\% $</tex></formula> , based on the pulse height spectra under <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{137}{\rm Cs}$</tex></formula> excitation. The afterglow level of CsI:In over 130 ms after pulsed X-ray excitation was two orders of magnitude higher than that of CsI:Tl.

Comparative study of Tm-doped and Tm-Sc co-doped Lu3Al5O12 scintillator

The crystals of Tm doped and Tm-Sc co-doped Lu3Al5O12 (LuAG) grown by the floating zone (FZ) method were examined for their optical and scintillation properties. In transmittance spectra, strong absorption lines due to Tm3+ 4f–4f transitions were observed. X-ray excited radioluminescence spectra were measured and broad and sharp emission peaks were detected. The former one was attributed to Sc3+ and the latter one was due to Tm3+ 4f–4f transitions. Scintillation yield enhancement due to Sc co-doping was observed by means of 137Cs pulse height spectra. Scintillation decay times were several tens of μs under pulse X-ray excitation.

Spectroscopy of composite scintillators

The spectral and temporal characteristics of X-ray luminescence of composites consisting of microparticles of “heavy” components (oxides, fluorides, sulfates) and an organic polymer binder containing optically active impurities have been investigated. It has been found that, in the case of pulsed X-ray excitation of the composites with a photon energy of 130–150 keV, the fast component (τ < 10 ns) of the luminescence arises whether or not the “heavy” component of the composite is doped with an optically active impurity. A mechanism has been proposed for the formation of the fast component of the luminescence: electrons and low-energy X-ray photons generated during the interaction of high-energy X-ray photons with the “heavy” component of the composite are effectively absorbed by the polymer binder and, thus, induce its luminescence. It has been shown that, in order to produce a composite-based fast scintillator with a high light yield, it is necessary to use a binder prepared from an organic material with a short scintillation decay time and another component prepared from a compound whose composition includes an element of a large atomic number Z.

Pulsed X-ray luminescence of composites consisting of inorganic particles and organic phosphors

A fast luminescence component with a duration of ∼2 ns has been observed upon pulsed X-ray excitation of composites composed of microparticles of a heavy constituent (heavy-metal oxides and fluorides) and optically active polymer adhesive. The intensity and temporal parameters of this component depend on neither the structural state of the heavy constituent nor the presence of optically active impurity. A mechanism of the formation of the fast luminescence component of composites upon pulsed X-ray excitation is proposed; according to it, when high-energy X rays interact with the heavy constituent of the composite, electrons and low-energy X-ray photons, which are intensely absorbed by the polymer adhesive and thus cause its luminescence, are generated due to the photoelectric effect and X-ray scattering.