Fast Decay Component Research Articles

Relaxation-induced dipolar exchange with recoupling (RIDER) distortions in CODEX experiments.

Chemical shift anisotropy (CSA) and dipolar CODEX (Cenralband Only Detection of EXchange) experiments enable abundant quantitative information on the reorientation of the CSA and dipolar tensors to be obtained on millisecond-second timescales. At the same time, proper performance of the experiments and data analysis can often be a challenge since CODEX is prone to some interfering effects that may lead to incorrect interpretation of the experimental results. One of the most important such effects is RIDER (relaxation-induced dipolar exchange with recoupling). It appears due to the dipolar interaction of the observed nuclei with some other nuclei, which causes an apparent decay in the mixing time dependence of the signal intensity reflecting not molecular motion, but spin flips of the adjacent nuclei. This may hamper obtaining correct values of the parameters of molecular mobility. In this contribution we consider in detail the reasons why the RIDER distortions remain even under decoupling conditions and propose measures to eliminate them. That is, we suggest (1)using an additional filter between the cross-polarization (CP) section and the CODEX recoupling blocks that suppresses the interfering anti-phase coherence responsible for the -H RIDER and (2)recording only the cosine component of the CODEX signal since it is less prone to the RIDER distortions in comparison to the sine component. The experiments were conducted on rigid model substances as well as microcrystalline H N-enriched proteins (GB1 and SH3) with a partial back-exchange of labile protons. Standard CSA and dipolar CODEX experiments reveal a fast-decaying component in the mixing time dependence of N nuclei in proteins, which can be misinterpreted as a slow overall protein rocking motion. However, the RIDER-free experimental setup provides flat mixing time dependences, meaning that the studied proteins do not undergo global motions on the millisecond timescale.

Stability and temporal decay of nanopatterned tribocharge on nanotextured elastomer surfaces

Contact electrification of nanotextured elastomer surfaces often generates nanopatterned tribocharges that are useful for both scientific and practical purposes. For sustained utilization of the nanopatterned tribocharge, their stability and temporal behavior must be characterized and studied. It is, however, a highly challenging task as it requires long-term, repeated probing of the tribocharge at the nanoscale spatial resolution. In this work, we performed such a comprehensive experimental study of nanopatterned tribocharges on elastomer surfaces using Kelvin probe force microscopy (KPFM) and electrostatic force microscopy (EFM). Curve-fitting analysis of the KPFM results not only affirmed the temporally decaying nature of the tribocharge but also separated them into two distinct, fast and slowly decaying, components that could be attributed to two different tribocharging mechanisms. Through pre-constrained optimization of the curve-fitting parameters and comparison of the results, we could attribute the fast and slow decay components to the tribocharges generated by tangential sliding and surface-normal separation of the material interface, respectively. The analysis also enabled us to estimate time-invariant “pedestal” potentials from the KPFM results and predict the existence of long-term stable tribocharge on the nanotextured elastomer surface. We experimentally confirmed it by re-scanning the specimens 14 days after the initial measurements. The observations, analysis, and the mechano-triboelectric charging model will benefit not only the researchers of nanoscale tribocharges but also those interested in the study and applications of triboelectricity in general. • Observed how nanopatterned tribocharge decays in time using long-term KPFM. • Identified fast and slow decays and correlated them with surface nano-morphology. • Attributed the two tribocharges to different triboelectrification mechanisms. • Predicted long-term stable tribocharge and confirmed it via KPFM at the 14th day.

Nonlinear absorption and the ultrafast dynamic process of Au-Ag nanoshuttles

Nonlinear optical absorption of Au-Ag nanoshuttles (NSs) was studied using an open-aperture Z-scan experiment with a 532 nm nanosecond laser at different energies. It was found that, when the laser energy is relatively low, the Au-Ag NSs exhibit saturated absorption (SA). When the laser energy is high, a conversion from SA to reverse saturated absorption (RSA) occurs. The ultrafast dynamic process of Au-Ag NSs was also investigated by using a femtosecond pump-probe technique. It is found that the process contains a fast and slow decay component that depends strongly on the laser intensity. Furthermore, when the probe wavelength is far away from the plasma resonance peak, the decay shows modulation due to the vibration mode of the coherent excitation.

Picosecond Lifetime Hot Electrons in TiO2 Nanoparticles for High Catalytic Activity

A large number of studies have examined the origins of high-catalytic activities of nanoparticles, but very few have discussed the lifetime of high-energy electrons in nanoparticles. The lifetime is one of the factors determining electron transfer and thus catalytic activity. Much of the lifetime of electrons reported in the literature is too short for a high transfer-efficiency of photo-excited electrons from a catalyst to the attached molecules. We observed TiO2 nanoparticles using the femtosecond laser two-color pump-probe technique with photoemission electron microscopy having a 40 nm spatial resolution. A lifetime longer than 4 ps was observed together with a fast decay component of 100 fs time constant when excited by a 760 nm laser. The slow decay component was observed only when the electrons in an intermediate state pumped by the fundamental laser pulse were excited by the second harmonic pulse. The electronic structure for the asymmetry of the pump-probe signal and the origin of the two decay components are discussed based on the color center model of the oxygen vacancy.

Electron-transfer behaviors between photoexcited metal complex and methyl viologen codoped in ionic nanospheres

In this study, we investigated photo-induced electron transfer (PET) dynamics from [Ru(bpy)3]2+ to MV2+ codoped in ionic nanospheres by picosecond time-resolved luminescence spectroscopy. The luminescence from [Ru(bpy)3]2+ was decreased with an increase of the MV2+ content in nanospheres, suggesting an electron transfer from the 3MLCT excited state of [Ru(bpy)3]2+ to MV2+. The fast decay component with the time-constant of 62 ns was found in the luminescence decay kinetics. This component is associated with a Perrin-type electron transfer and increases with an increase of the MV2+ content, suggesting the efficient Perrin-type electron transfer in the higher MV2+ content. In addition, the decay component of 280∼410 ns depending on a MV2+ concentration is explained by the dynamic-type electron transfer since the inverse lifetime of this component exhibits the linear dependence on the MV2+ content. The Perrin- and dynamic-type electron transfer rates were determined to be 1.4 × 107 s−1 and 7.8 × 10−3 nmol−1 mg μs−1, respectively. The PET efficiency was determined 70 % in ionic nanospheres containing 92 nmol/mg of [Ru(bpy)3]2+ and 152 nmol/mg of MV2+.

Slow carrier cooling in methylammonium lead bromide quantum dots: Evidence of hot phonon bottleneck

Photoinduced charge carrier dynamics studies in lead halide perovskites helps in explaining key processes like carrier trapping, diffusion and multiexciton dynamics etc. which are of importance to understand the fate of excitons. In the present study, we investigate the dynamics in methylammonium lead bromide perovskite nanocrystals under low and high pump intensity to study hot carrier cooling mechanisms. The single exciton studies conducted under low pump fluences (<N> = 0.3) revealed slow carrier decay with a significant fraction of >1 ns decay times as expected due to long radiative carrier recombination times. This also indicated that fast carrier trapping does not occur as evidenced by absence of any fast decay components. The hot carrier (HC) cooling mechanisms were verified by studying carrier density dependence of carrier temperature decays as extracted from the higher energy part of exciton bleach. These studies revealed a very fast cooling of ∼150 fs under low carrier density 1.5 × 1017/ cm3. However additional experiments under higher carrier densities of ∼1018-1019/cm3 showed a very slow carrier temperature decay with decay time ∼100 ps for the highest intensity investigated. The analysis of hot carrier lifetimes revealed Auger heating and acoustic phonon up-conversion as reason for hot carrier relaxations at higher intensities. Additionally, we carried out experiments under hole quencher, we found lower initial carrier temperatures and faster decay indicating highly efficient hole transfer to the quencher in a time scale faster than cooling of carrier at higher intensities. These results hint at possibility of molecular design for enabling efficient hot carrier extraction from these Quantum Dots (QDs).

Advances in High-Resolution Ultrafast LuI3:Ce Scintillators for Fast Timing Applications

Scintillation detectors exhibiting high spatial resolution and fast timing capabilities are of vital importance for synchrotron sources. These detectors may be exposed to a variety of X-ray energies (up to 140 keV) and used in high frame rate applications. Here, we describe the advances in the development of thin-film LuI3:Ce scintillators for higher energy X-ray imaging, with fast timing and high spatial resolution. When grown in a single crystalline form, these scintillators are bright, producing 115 000 photons/MeV. However, to achieve high spatial resolution, these scintillators are grown in thin-film form with a microcolumnar structure, controllable to column diameters of $30~\mu \text{m}$ . Thus, a much thicker scintillator layer ( $10~\mu \text{m}$ –3 mm or higher) may be grown, providing superior X-ray absorption while achieving high resolutions of $50~\mu \text{m}$ or better, at the cost of reduced light yield. To study the timing characteristics of the scintillator, time-resolved X-ray excited optical luminescence (TR-XEOL) was performed on two different sets of three samples of LuI3 at the 1-BM beamline of the Advanced Photon Source at Argonne National Laboratory. Besides, we report timing measurements obtained using a photomultiplier tube (PMT) and oscilloscope at Radiation Monitoring Devices (RMD) Inc. Using the TR-XEOL, we determined the decay constants of LuI3 as a function of Ce doping, recording a fast decay component as low as 3.6 ns (39%), one of the fastest values recorded in inorganic scintillators. This fast decay opens up numerous novel applications, where ultrahigh frame rates are important using synchrotron X-rays. This article will discuss fabrication, characterization, and potential applications for this novel scintillator.

Resonant enhancement of nonlinear absorption and ultrafast dynamics of WS2 nanosheets

The comparative study on nonlinear absorption of WS2 nanosheets was performed by using nanosecond Z-scan measurements at 532 nm and 500 nm. It was found that, WS2 nanosheets exhibit saturable absorption (SA) at low excitation intensities, and the saturable intensity at 500 nm is much stronger than that at 532 nm, which implies that resonance plays main role. With the increase of incident intensity, a switch from SA to reverse saturable absorption (RSA) occurs. Besides, ultrafast dynamics of WS2 nanosheets were investigated by using femtosecond pump-probe technique. Photo-dynamics process was found to contain a double exponential energy relaxation with a fast decay component (14 ps) and a slow one (145 ps).

Investigation of cross luminescence in lanthanum fluoride as a potential fast-response scintillator

We report the potential of lanthanum fluoride (LaF3) as a fast-response scintillator. When excited by an extreme ultraviolet free electron laser, neodymium-doped LaF3 (Nd3+:LaF3) exhibited a 1.9 ns fast decay component and a 6.7 ns slow decay component for its 172 nm emission peak. The slow decay component is due to interconfigurational 4f25d-4f3 transition in Nd3+. First principles density functional theory calculations using the Perdew–Burke–Ernzerhof hybrid functional including exact exchange (PBE0) and the Green’s function and screened Coulomb interaction (GW) approximation as implemented in the Vienna Ab initio Simulation Package using plane-wave basis sets within the projector-augmented wave method elucidate the electronic structure of LaF3 and reveal that the fast decay component could be due to partial cross luminescence (CL) from the bottom of the valence band to the top of the outermost core band. The presence of CL alludes to the potential of LaF3 as a fast-response scintillator.

Impact of nitrogen induced defect dynamics on UV response of diamond photodetectors

Abstract This work correlates the ultraviolet (UV) current response of single-crystal diamond photodetectors to the lifetimes of nitrogen-induced color centers. Single-crystal diamond photodetectors are fabricated and characterized by optical and electrical measurements. The optical characterizations include Raman spectroscopy, Photoluminescence spectroscopy (PL) and the Time Resolved Photoluminescence (TR-PL) measurements. The electrical characterizations include the capacitance-voltage (C–V), current-voltage (I–V), and UV response current measurements. As observed from the photocurrent studies, the magnitude of the current response rises up to five order in the voltage range ±100V in comparison to the dark condition. The charge carrier dynamics of the dominant color centers contributing to the response have been analysed quantitatively through UV response, PL and TR-PL measurements. TR-PL studies reveal that the faster component of the decay can be associated with the Shockley Read Hall (SRH)- nonradiative recombination which decreases with the increase in nitrogen concentration. The decay period corresponding to the slower component is attributed to the radiative recombination at the color centers.

Tungsten co-doping effects on Ce:Gd3Ga3Al2O12 scintillator grown by the micro-pulling down method

Single crystal scintillators are extensively used in various radiation detection applications and their scintillation performances can be improved via co-doping. Therefore, in this study, tungsten-ion co-doped Ce:Gd3(Ga,Al)5O12 (Ce:GGAG) crystals were grown using the micro-pulling-down (μ-PD) method to investigate the effects of co-doping on their scintillation properties. The relationships between the W concentration, optical and luminescence properties, and radiation response of the W-co-doped Ce:GGAG crystals were evaluated. The W-co-doped Ce 0.5%:Gd3Ga3Al2O12 single crystals of diameter 3 mm and length 30–60 mm were grown by the μ-PD method. The light yield increased at W concentrations of 200 and 500 ppm and decreased at W concentrations above 1000 ppm. There was no significant change in the fast decay component of scintillation.

Blind Source Separation for Myelin Water Fraction Mapping Using Multi-Echo Gradient Echo Imaging.

In conventional gradient-echo myelin water imaging (GRE-MWI), myelin water fraction (MWF) is estimated by fitting the multi-echo gradient recalled echo (mGRE) signal to a pre-assumed numerical model (e.g., multi-component exponential curves or three component exponential curves). However, in mGRE, imaging artifacts (e.g., voxel spread function and physiological noise) and noise render the signal to deviate from the numerical model, leading to misfit of the model parameters. Here, as an alternative to the model-based GRE-MWI, a blind source separation (BSS) technique for the separation of multi-exponential mGRE signal is proposed. Among the various BSS techniques, a modified robust principal component analysis (rPCA) is presented to separate signal sources by enforcing the data-driven properties such as "low rankness" and "sparsity." Considering the signal evolution of T2∗ relaxation (i.e., non-negative exponential decay), low rankness of exponential decay was enforced by nonnegative matrix factorization (NMF) and hankelization. This method provides the separation of slow-decaying, fast-decaying exponential components and artifact components from mGRE images. After the separation, MWF map is reconstructed as the ratio of the fast-decaying component to the total decaying components. The proposed method was demonstrated in numerical simulations and in vivo scans. The method provided a robust estimation of MWF in the presence of statistical noise and imaging artifacts.

Czochralski growth and scintillation properties of Li+, Na+, and K+ codoped (Lu0.75, Y0.25)3Al5O12: Pr3+ single crystals

Abstract In this paper, we explore codoping with monovalent ions: Li+, Na+, and K+, as a method of altering the scintillation properties of praseodymium-doped (Lu0.75Y0.25)3Al5O12 (LuYAG: Pr3+) single crystals. Substantial effort was given to optimizing the growth process to mitigate cracking which occurred in the LuYAG crystals beginning around the shoulder region and continuing throughout the boule. Growth parameters such as the translation and rotation rate, cool down duration, and boule geometry were altered to successfully address this challenge. Scintillation light yield, energy resolution, and scintillation decay time were measured for each of these crystals. It was discovered that monovalent codoping significantly improved scintillation light yield by at least 50%; accelerated and increased the weight of the fast component of scintillation decay; and enhanced energy resolution to values of as low as 3.8%, the best energy resolution reported for an oxide scintillator to date. The enhancements in scintillation performance are related to the effect of monovalent codoping on the formation of defects, in particular oxygen vacancies, within the LuYAG matrix and is proven via thermoluminescence and afterglow measurements.

Luminescent Properties of Borosilicate Glass Doped with Cerium

ABS–BGP glasses (Al2O3–B2O3–SiO2–BaCO3–Gd2O3–P2O5) doped with different concentrations of Ce3+ ions are synthesized by the high-temperature melting technique. Optical, structural, and luminescence properties were studied. Emission connected with the transitions of Ce3+ ions is recorded in a spectral region of 350–550 nm. The luminescence decay kinetics is characterized by two components: fast and slow. The fast decay component is 45–90 ns; decreasing decay time of the slow component from 4 to 0.9 μs is observed with increasing cerium ion concentration. Based on the obtained results, it is assumed that Ce3+ ions exist in different emission states in the borosilicate glass.

Dark current–voltage characteristics of vacuum deposited multilayer amorphous selenium-alloy detectors and the effect of x-ray irradiation

Doped and stabilized amorphous selenium (a-Se) alloys in a multilayer form are currently used as a photoconductor in direct conversion flat panel x-ray imagers in mammography and tomosynthesis. While much progress has been made on the physics of such detectors, there are still unresolved questions on such issues as the principles of operation of the so-called p-i-n detector structure in extinguishing the dark current. The present paper examines dark current transients after the application of a voltage in seven types of a-Se alloy based devices: i-layer, i-n, n-i, i-p, p-i, p-i-n, and n-i-p structures. The substrate was ITO coated glass, the top (radiation receiving) electrode was chromium, and the films were fabricated by vacuum deposition. The nominal device thickness was 200 μm, similar to commercial mammographic detectors. It is shown that n-i, i-n, n-i-p, and p-i-n devices have dark currents less than 1 pA mm−2 at an applied field of 10 V/μm. The dark current in the p-i-n device is the lowest at approximately 0.01 pA mm−2 at an applied field of 10 V μm−1. Experiments have been carried out by subjecting the detector to a staircase voltage-time profile during the voltage application (turn-on) and a staircase voltage ramp-down during the turning-off of the bias voltage. Step-voltage ramp-up and step-voltage ramp-down current transient are typical of expected dark current transient behavior in a semiconductor with traps in which carriers are captured and released from various trap centers in the bandgap. The dark current transients are qualitatively similar to those expected from a capacitor in parallel with a large resistor and both in series with a much smaller resistor. Current transients during charging and discharging experiments were integrated to find how much of the injected charge is released during discharge experiments. It is shown that the majority of this trapped charge is stored in the n-type and p-type blocking layers, near the contacts. The trapped carriers in the i-layer represent a very small portion. The evolution of the dark current upon single and repeated x-ray exposure has also been examined in n-i and p-i-n devices. Right after the cessation of irradiation, there is an excess or residual dark current whose magnitude is roughly ∼20 times higher in p-i-n and about ∼2 times higher in the case of n-i under an exposure of 3.36 R and a mean photon energy of 34.2 keV. The absorbed dose is 1.53 Gy. The excess dark current has a fast decay component with a time constant ∼10 s and a slow component with a time constant ∼100 s. It is shown that the decay in the irradiation induced excess dark current is very similar to the initial dark current. There is no permanent change in the dark current, and within a few hundred seconds, the dark current reaches the same level as that in the unexposed detector. The experimental results in this work highlight the distinct advantages of p-i-n and n-i-type a-Se multilayer structures in x-ray detection applications.

Abbreviated quantitative UTE imaging in anterior cruciate ligament reconstruction

BackgroundExisting ultrashort echo time magnetic resonance imaging (UTE MRI) methods require prohibitively long acquisition times (~ 20–40 min) to quantitatively assess the clinically relevant fast decay T2* component in ligaments and tendons. The purpose of this study was to evaluate the feasibility and clinical translatability of a novel abbreviated quantitative UTE MRI paradigm for monitoring graft remodeling after anterior cruciate ligament (ACL) reconstruction.MethodsEight patients who had Graftlink™ hamstring autograft reconstruction were recruited for this prospective study. A 3D double-echo UTE sequence at 3.0 Tesla was performed at 3- and 6-months post-surgery. An abbreviated UTE MRI paradigm was established based on numerical simulations and in vivo validation from healthy knees. This proposed approach was used to assess the T2* for fast decay component ( {T}_{2s}^{ast } ) and bound water signal fraction (fbw) of ACL graft in regions of interest drawn by a radiologist.ResultsCompared to the conventional bi-exponential model, the abbreviated UTE MRI paradigm achieved low relative estimation bias for {T}_{2s}^{ast } and fbw over a range of clinically relevant values for ACL grafts. A decrease in {T}_{2s}^{ast } of the intra-articular graft was observed in 7 of the 8 ACL reconstruction patients from 3- to 6-months (− 0.11 ± 0.16 ms, P = 0.10). Increases in {T}_{2s}^{ast } and fbw from 3- to 6-months were observed in the tibial intra-bone graft ( {varDelta T}_{2s}^{ast } : 0.19 ± 0.18 ms, P < 0.05; Δfbw: 4% ± 4%, P < 0.05). Lower {T}_{2s}^{ast } (− 0.09 ± 0.11 ms, P < 0.05) was observed at 3-months when comparing the intra-bone graft to the graft/bone interface in the femoral tunnel. The same comparisons at the 6-months also yielded relatively lower {T}_{2s}^{ast } (− 0.09 ± 0.12 ms, P < 0.05).ConclusionThe proposed abbreviated 3D UTE MRI paradigm is capable of assessing the ACL graft remodeling process in a clinically translatable acquisition time. Longitudinal changes in {T}_{2s}^{ast } and fbw of the ACL graft were observed.

Exciton dynamics as a function of excitation intensity and double-pulse excitation in cyanine molecule thin films: Toward low-power optical switches

Exciton decay dynamics can be optically controlled by changing the excitation conditions, particularly, the excitation intensity. In this study, we report how the exciton dynamics in cyanine thin films depend on the excitation intensity and sequence. The excitons in these films have two decay components, and the ratio of the population of the fast decay component to the total population depends on the excitation intensity. Conversely, sequential excitation by a second optical pulse does not alter this ratio. Although the total excitation power is comparable, the change in the dynamics by the second pulse is different from the simple increase in the excitation power. Therefore, the sequential excitation by the second pulse can be a key point for realizing low-power optical switches.

Polar axis oriented crystal growth induced carrier transport characteristics in non-degenerate zinc oxide thin films grown on glass substrates

Abstract The predominance of the methanol, ethanol, and 2-methoxyethanol solvents, with different boiling points and dielectric constants, are observed on the crystal growth orientation, optical behavior, carrier recombination, and carrier transport mechanism in sol-gel spin coated ZnO thin films. Multi-axis oriented crystal growth orientation was observed for methanol processed ZnO film as compared to that along c-axis only while using other solvents. The intensity of c-axis orientation, crystallite size as well as radiative recombination luminescence effects follows a direct (or inverse) relationship with the boiling point (or dielectric constant) of the involved solvent. Diverse nature of stress was seen for the films. Ideal band gap value (3.36 eV) was identified for 2-methoxyethanol processed oxygen defects induced stress free ZnO thin films. Time resolved photoluminescence (TRPL) spectra reveal a significant contribution of ultrafast and fast decay components in ethanol and methanol processed films as compared to the dominance of slow decay components in 2-methoxyethanol processed thin film. The temperature dependent electrical resistivity measurements unfold the coexistence of metallic and semiconducting behavior in all films. Dominant optical phonon scattering and piezoelectric scattering mechanisms provide metallic behavior to the films as confirmed by an increasing resistivity with increased temperature. The dominant grain boundary scattering mechanism controls the mobility of the carriers and results in the semiconducting behavior in all films at different values of higher temperatures. We have quantified the crystallite size induced band bending effect to understand the applicability of ZnO films in optoelectronic devices as well.

Decay Dynamics and Diffusion Lengths of Bright and Dark Excitons in Air-Suspended Carbon Nanotubes

As excitonic states play an important role in optical phenomena [1] in carbon nanotubes, their fundamental properties such as emission lifetime and diffusion length have been studied by various optical techniques [2]. In the lowest lying states of excitons, however, there exist other “dark” states, whose properties are not well understood yet because they are not optically accessible. Here we separately investigate exciton dynamics of parity-odd bright state and parity-even dark state by performing time-resolved photoluminescence measurements on defect-free as-grown carbon nanotubes. The emission decay curves exhibit bi-exponential behavior, where the fast and slow decay components arise from the dynamics of bright and dark excitons, respectively. We analyze such exciton dynamics using a three-level model including the effects of end quenching by measuring chirality-identified nanotubes with different suspended lengths [Fig. 1]. We find that bright excitons have lifetimes of ~70 ps and diffusion lengths of several hundred nanometers, consistent with the known values. In comparison, dark excitons have much longer lifetimes in the order of nanoseconds and diffusion lengths longer than 3 μm. We also observe a tendency that nanotubes with larger diameter have higher bright-dark transition rate, which is likely due to the diameter dependence of the splitting energy between bright and dark states. Work supported by JSPS (KAKENHI JP16K13613 and JP17H07359), MEXT (Nanotechnology Platform), and RIKEN (Incentive Research Project). H.M. acknowledges support by RIKEN Junior Research Associate Program. [1] A. Ishii, T. Uda, Y. K. Kato, Phys. Rev. Appl. 8, 054039 (2017).[2] A. Ishii, M. Yoshida, Y. K. Kato, Phys. Rev. B 91, 125427 (2015).Fig.1 Emission decay curves obtained from (9,8) nanotubes with various lengths ranging from 0.5 μm (purple) to 4.2 μm (red). The gray line indicates the instrument response function. (inset) Schematic of the three-level model for exciton decay dynamics. Figure 1

Scintillation properties of Gd3Al2Ga3O12:Ce, Li and Gd3Al2Ga3O12:Ce, Mg single crystal scintillators: A comparative study

The scintillation characteristics of Gd3Al2Ga3O12:Ce, Li (GAGG:Ce,Li) and Gd3Al2Ga3O12:Ce, Mg (GAGG:Ce,Mg) single crystals were compared. Radioluminescence spectra and photoluminescence decay curves were measured at various temperatures between 77 and 500 K to investigate the thermal luminescence quenching. At 662 keV γ rays, the LY value of 35,400 photons/MeV and energy resolution of 6.9% obtained for GAGG:Ce, Li are superior to those of 24,200 photons/MeV and 9.5% for GAGG:Ce,Mg. Scintillation decays are approximated by a double exponentials with a fast principal decay component of 47 ns (83%) for GAGG:Ce, Mg and 90 ns (86%) for GAGG:Ce,Li. Coincidence time resolution of 282 ps obtained for GAGG:Ce, Mg is better than that of 389 ps for GAGG:Ce,Li. GAGG:Ce, Mg shows a much lower afterglow and thermally stimulated luminescence intensity with respect to GAGG:Ce,Li.