Cerium-doped Lutetium Oxyorthosilicate Research Articles

A-Si EPID Modeling in GATE for Monte Carlo Investigation on the Optical Properties of Gd<sub>2</sub>O<sub>2</sub>S:Tb and Lu<sub>2</sub>SiO<sub>5</sub>:Ce Scintillators

A detailed a-Si Electronic Portal Imaging Device (EPID) was implemented in GATE (Geant4 application for tomographic emission) toolkit for Monte Carlo simulations, employing the standard electromagnetic processes and optical photon processes. The composition of the scintillating material is varied using the conventional terbium-doped gadolinium oxysulfide phosphor (Gd2O2S:Tb) and cerium-doped lutetium oxyorthosilicate (Lu2SiO5:Ce) which is widely used in Positron Emission Tomography (PET) detectors due to its supremacy in aiding the detection of low-energy photons. It was found that the number of optical photons produced is higher when using the Lu2SiO5:Ce scintillator resulting in a slightly better signal-to-noise ratio (SNR). The scattering within the EPID components was also investigated where the majority of the detected secondary particles were created in the scintillator. The results also show that the copper plate layer of the EPID contributes to additional Compton electrons and bremsstrahlung and annihilation photons to the measurements in the scintillator and photodiode layer. The glass substrate, graphite plates, electronic components, and aluminum bottom cover are also found to contribute a huge fraction of backscattered particles to the measurements at the photodiode layer.

A novel method for investigating optically stimulated luminescence in scintillators

Optically stimulated luminescence (OSL) is a known property in many scintillators, and investigating the branching ratio of thermalized carriers to this photon-emission mechanism could aid both scintillator development and OSL-based dosimetry. We present a novel method for determining the branching ratio of thermalized carriers to OSL in scintillators while monitoring the energy deposition from 511 keV gamma photons on an event-by-event basis. We demonstrate the method using a cerium-doped lutetium oxyorthosilicate (LYSO:Ce) crystal, and validate that the observed signal indeed originates from OSL photons by estimating the lifetime of the OSL traps, which is consistent with values found in the literature. We report a branching ratio of thermalized carriers to the OSL traps in LYSO:Ce of (1.0±0.2)% upon excitation with 511 keV gamma photons, using a one-trap-one-recombination-center model.

Investigation of phase evolution and Gd occupation in (Lu1-xGdx)2SiO5 lattice by Rietveld refinement and DFT simulation

Cerium-doped lutetium oxyorthosilicate (LSO:Ce, Lu2SiO5:Ce) is considered to be a typical scintillator with comprehensive good scintillation properties. The doping of Gd3+ elements with different concentrations strongly influences the structure and luminescence performance of LSO. The full concentration range of LGSO ((Lu1-xGdx)2SiO5) powders were prepared using a sol-gel method. The influences of the doping Gd3+ ion concentration on the phase evolution and lattice parameters of LGSO were investigated via X-ray diffraction (XRD), Rietveld refinement and density functional theory (DFT) simulations. It was found that the monoclinic crystal structure of LGSO gradually transitioned from C2/c to P21/c under elevated temperatures and phase transition temperature varied from 975 to 1400 ​°C as Gd replaced Lu. The lattice constants (a, b, and c) of LGSO lattice increased with the addition of Gd. The Rietveld refinement results indicate that doping Gd3+ in LGSO was prone to occupy the RE1 site rather than the RE2 site and Gd dopants was easily to form GdRE1-GdRE1 defect complex. The formation energy results of Gd3+ replacing different Lu3+ sites calculated by using the first-principles pseudopotential approach further proved this occupation mode. The intensity of photoluminescence of Ce:(Lu1-xGdx)2SiO5 attained the peak value when the content of Gd doping reached 0.05.

Feasibility of cerium-doped LSO particles as a scintillator for x-ray induced optogenetics

Objective. Non-invasive light delivery into the brain is needed for in vivo optogenetics to avoid physical damage. An innovative strategy could employ x-ray activation of radioluminescent particles (RLPs) to emit localized light. However, modulation of neuronal or synaptic function by x-ray induced radioluminescence from RLPs has not yet been demonstrated. Approach. Molecular and electrophysiological approaches were used to determine if x-ray dependent radioluminescence emitted from RLPs can activate light sensitive proteins. RLPs composed of cerium doped lutetium oxyorthosilicate (LSO:Ce), an inorganic scintillator that emits blue light, were used as they are biocompatible with neuronal function and synaptic transmission. Main results. We show that 30 min of x-ray exposure at a rate of 0.042 Gy s−1 caused no change in the strength of basal glutamatergic transmission during extracellular field recordings in mouse hippocampal slices. Additionally, long-term potentiation, a robust measure of synaptic integrity, was induced after x-ray exposure and expressed at a magnitude not different from control conditions (absence of x-rays). We found that x-ray stimulation of RLPs elevated cAMP levels in HEK293T cells expressing OptoXR, a chimeric opsin receptor that combines the extracellular light-sensitive domain of rhodopsin with an intracellular second messenger signaling cascade. This demonstrates that x-ray radioluminescence from LSO:Ce particles can activate OptoXR. Next, we tested whether x-ray activation of the RLPs can enhance synaptic activity in whole-cell recordings from hippocampal neurons expressing channelrhodopsin-2, both in cell culture and acute hippocampal slices. Importantly, x-ray radioluminescence caused an increase in the frequency of spontaneous excitatory postsynaptic currents in both systems, indicating activation of channelrhodopsin-2 and excitation of neurons. Significance. Together, our results show that x-ray activation of LSO:Ce particles can heighten cellular and synaptic function. The combination of LSO:Ce inorganic scintillators and x-rays is therefore a viable method for optogenetics as an alternative to more invasive light delivery methods.

Effect of SiO2 on the sintering of cerium-doped lutetium oxyorthosilicate

We present the effect of silica on the preparation of dense Lu2SiO5:Ce (LSO:Ce) compacts. Powders of LSO:Ce were first obtained by combustion synthesis and characterized by thermal analysis, indicating the presence of free amorphous silica in amounts approaching 5 wt%. Calcination treatments at a variety of temperatures resulted in the partial volatilization of the silica and the formation of B-type LSO. However, higher temperatures enhanced agglomeration and particle growth, which can be problematic during the sintering process as it impedes full densification. During subsequent sintering of the powders, evaporation of residual silica may impede full densification and assist the formation of pores, thus an understanding of the presence of silica is important for sintering these materials. Powders calcined at a temperature of 1773 K and densified by spark plasma sintering showed the highest photoluminescence emission intensity. At this temperature there is a trade-off between decreasing electron trap density and oxidation of cerium ions.

LSO:Ce Inorganic Scintillators Are Biocompatible With Neuronal and Circuit Function.

Optogenetics is widely used in neuroscience to control neural circuits. However, non-invasive methods for light delivery in brain are needed to avoid physical damage caused by current methods. One potential strategy could employ x-ray activation of radioluminescent particles (RPLs), enabling localized light generation within the brain. RPLs composed of inorganic scintillators can emit light at various wavelengths depending upon composition. Cerium doped lutetium oxyorthosilicate (LSO:Ce), an inorganic scintillator that emits blue light in response to x-ray or ultraviolet (UV) stimulation, could potentially be used to control neural circuits through activation of channelrhodopsin-2 (ChR2), a light-gated cation channel. Whether inorganic scintillators themselves negatively impact neuronal processes and synaptic function is unknown, and was investigated here using cellular, molecular, and electrophysiological approaches. As proof of principle, we applied UV stimulation to 4 μm LSO:Ce particles during whole-cell recording of CA1 pyramidal cells in acute hippocampal slices from mice that expressed ChR2 in glutamatergic neurons. We observed an increase in frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs), indicating activation of ChR2 and excitation of neurons. Importantly, LSO:Ce particles did not affect survival of primary mouse cortical neurons, even after 24 h of exposure. In extracellular dendritic field potential recordings, no change in the strength of basal glutamatergic transmission was observed during exposure to LSO:Ce microparticles. However, the amplitude of the fiber volley was slightly reduced with high stimulation. Additionally, there was a slight decrease in the frequency of sEPSCs in whole-cell voltage-clamp recordings from CA1 pyramidal cells, with no change in current amplitudes. The amplitude and frequency of spontaneous inhibitory postsynaptic currents were unchanged. Finally, long term potentiation (LTP), a synaptic modification believed to underlie learning and memory and a robust measure of synaptic integrity, was successfully induced, although the magnitude was slightly reduced. Together, these results show LSO:Ce particles are biocompatible even though there are modest effects on baseline synaptic function and long-term synaptic plasticity. Importantly, we show that light emitted from LSO:Ce particles is able to activate ChR2 and modify synaptic function. Therefore, LSO:Ce inorganic scintillators are potentially viable for use as a new light delivery system for optogenetics.

Highly luminescent cerium-doped YSO/ LSO microcrystals prepared via room temperature sol-gel route

Luminescent properties of cerium-doped yttrium oxyorthosilicate (Y2SiO5; YSO) and lutetium oxyorthosilicate (Lu2SiO5; LSO) prepared by a room-temperature sol-gel route were studied and compared to those of YSO and LSO single crystals. Structural changes in the samples during calcination were also studied by X-ray diffraction and differential thermal analysis. Radioluminescence spectra of the samples show comparable emission intensity with the bulk materials. Photoluminescence decay measurements were used to investigate the decay characteristics of the prepared powders. Changes in luminescent properties after the reduction of particle size by grinding in a ball mill were also demonstrated on the YSO:Ce3+ sample. Acceleration of the faster component of the decay time from 7.1 ns to 6.2 ns was observed. Prepared YSO:Ce3+ and LSO:Ce3+ powders are suggested to be good candidates for fast imaging or other applications.

Ab-initio study of oxygen vacancy stability in bulk and Cerium-doped lutetium oxyorthosilicate

We study from first principles the stability of neutral and charged oxygen vacancies in lutetium oxyorthosilicate, Lu2SiO5, as well as its possible modification due to the presence of Ce3+, as present in commercial scintillators. We show that the neutral oxygen vacancy with the lowest formation energy forms at the oxygen sites within the [SiO4] tetrahedra instead of the interstitial oxygen site bonded exclusively to lutetium atoms. The discrepancy with a previous study is attributed to the quality of the pseudopotential. Support for these results is found by performing a bonding analysis of the oxygen sites, as well as oxygen vacancy calculations in the iso-structural Y2SiO5 compound. In addition, we find that the incorporation of Ce3+ ion does not affect the stability of oxygen vacancies in Lu2SiO5.

Cerium-doped lutetium oxyorthosilicate optical waveguide fabricated by ions irradiation: Modification of surface structures and optical properties

Ion beam technology has been a popular and established method to modify the optical properties of a large variety of crystal materials. In this study, the influence of C3+ ion irradiation at an energy of 6.0 MeV with a fluence of 5.0 × 1014 ions/cm2 on the optical properties, including waveguide and spectral properties, of Ce:Lu2SiO5 were investigated. First, the displacement per atom (dpa) and X-ray diffraction (XRD) were used to analyze the change in the lattice structure of the irradiated region. The waveguide properties were studied by the prism coupling and end-facing coupling techniques and discussed in terms of the reflectivity calculation method (RCM). The absorption spectra and Raman spectra were measured to analyze the absorption characteristics and molecular vibration of samples. The photoluminescence spectra before and after irradiation were investigated. The experimental results reveal that the intensity of the emission spectra is enhanced after C3+ ion irradiation.

The mechanochemical and solution combustion syntheses of cerium-doped lutetium oxyorthosilicate powder

Lu2SiO5:Ce powders have been synthesized by mechanochemical processing of the constituent oxides and by urea/hexamine-nitrate-based solution-combustion methods with microwave and furnace sintering of each material. Powder x-ray diffraction (PXRD), photoluminescence excitation (PLE) and emission (PL) spectroscopy, time-correlated single photon counting (TCSPC), particle size analysis (PSA), and scanning electron microscopy (SEM) have been used to characterize the resulting powders. Mechanochemical synthesis results in the formation of agglomerated powders with the C 1 2/c 1 symmetry while solution combustion leads to the formation of porous powders with a mixture of the C 1 2/c 1 and P 1 21/c 1 symmetries. This mixture transitions to the C 1 2/c 1 phase with sintering. Both syntheses result in particle sizes of less than 50 μm before sintering. Each material shows the typical luminescence from the 5d-4f transition in addition to decay times that match standard Ce3+ values.

Densification of cerium-doped lutetium oxyorthosilicate scintillation ceramics by hot isostatic pressing

The effects of presintering temperature, soak time, and Hot Isostatic Pressing (HIPing) temperature on the microstructure and densification behavior of cerium-doped lutetium oxyorthsilicate (Lu2SiO5:Ce, LSO:Ce) ceramics were investigated. It was determined that the most suitable presintering conditions (minimum presintering temperature and shortest soak time) required to obtain closed porosity were a 4 h dwell at 1650 °C in air. The optimal HIPing conditions to achieve full density were determined to be 1 h at 1650 °C under a 150 MPa Ar atmosphere. The luminescence decay time of the HIPed LSO:Ce ceramics is composited of a fast component of 10 ns (51%) and a slow component of 31 ns (49%), which is shorter than that of cerium-doped rare earth oxyorthsilicate single crystal. The light yield of the LSO:Ce ceramics reaches 21,000 photons/MeV, which is ∼95% of the value of a typical LSO:Ce single crystal.

Grain orientation control of cerium doped lutetium oxyorthosilicate ceramics in a strong magnetic field

Cerium-doped lutetium oxyorthosilicate (LSO:Ce) scintillator ceramics were fabricated by slip casting in a 9 T vertical magnetic field, followed by hot isostatic pressing (HIP) at 1650°C under 150MPa applied pressure. XRD and Electron Backscatter Diffraction (EBSD) mapping results reveal that the grains of the LSO:Ce ceramics are aligned along the [4¯02] crystallographic direction. The degree of texturing (Lotgering factor, f) of the ceramics was determined to be 0.28. Measurements revealed the in-line transmittance of the textured LSO:Ce ceramics to be 4.7 times that of the untextured ceramics, attaining a transmittance of 6.6% at 420nm (emission maximum).

Effects of Air Annealing on Luminescent Properties of Cerium-Doped Lutetium Oxyorthosilicate Scintillation Ceramics

Cerium-doped lutetium oxyorthosilicate ( ${\rm Lu}_{2}{\rm SiO}_{5}$ : 0.5 mol%Ce, LSO:Ce) scintillation ceramics was fabricated by pre-sintering at $1650^\circ {\rm C}$ for 4 h in air followed by a post hot isostatic pressing (HIP) at $1600^\circ {\rm C}$ under 150 MPa for 1 h in Ar atmosphere. Luminescent and scintillation properties of the as-HIPed LSO:Ce ceramics was seriously affected by these oxygen vacancies. They were effectively filled through a post-annealing at $1300^\circ {\rm C}$ for 4 h in air. Ce ${\rm L}_{\rm III}$ edge X-ray absorption near edge structure (XANES) spectra of LSO:Ce ceramics manifest that most of Ce ions in LSO ceramics still remain Ce(III) valence state after annealing in air. Photoluminescence (PL) and PL excitation (PLE) spectra show that emission intensity of the as-HIPed LSO:Ce ceramics was about 3 times lower than that of post-annealed sample. Light yield of the post-annealed LSO:Ce ceramics reaches 2.7 times of that of the as-HIPed sample, which exceeds 3 times of the light yield of BGO crystal.

Conical photonic crystals for enhancing light extraction efficiency from high refractive index materials.

We propose, analyze and optimize a two-dimensional conical photonic crystal geometry to enhance light extraction from a high refractive index material, such as an inorganic scintillator. The conical geometry suppresses Fresnel reflections at an optical interface due to adiabatic impedance matching from a gradient index effect. The periodic array of cone structures with a pitch larger than the wavelength of light diffracts light into higher-order modes with different propagating angles, enabling certain photons to overcome total internal reflection (TIR). The numerical simulation shows simultaneous light yield gains relative to a flat surface both below and above the critical angle and how key parameters affect the light extraction efficiency. Our optimized design provides a 46% gain in light yield when the conical photonic crystals are coated on an LSO (cerium-doped lutetium oxyorthosilicate) scintillator.

Optical properties and electronic structure of Lu2SiO5 crystals doped with cerium ions: Thermally-activated energy transfer from host to activator

This paper reports on the optical properties of cerium-doped lutetium oxyorthosilicate (LSO:Ce) crystals. The reflection and X-ray photoelectron spectra are measured, and compared to the electronic structure calculated by a discrete variational Xα method. A sharp exciton band originating from O 2p→Lu 5d transition is observed at 7.27eV at 6K, with the band-gap energy of 7.52eV. Luminescence measurements have also been performed in a wide temperature range of 6–300K. The intensity of Ce luminescence arising from the 5d→4f transition is temperature-independent under the direct excitation of Ce3+ ions, but it is enhanced at around 50K under the excitation of host LSO crystals. This enhancement is found to anti-correlate with a thermal quenching of the intrinsic luminescence due to self-trapped excitons. The present results provide a piece of evidence that thermally-activated energy transfer from host to activator takes place efficiently in LSO:Ce.

Effects of Photonic Crystals on the Light Output of Heavy Inorganic Scintillators

Photonic crystals (PhCs) are optical materials which can affect the propagation of light in multiple ways. In recent years PhCs contributed to major technological developments in the field of semiconductor lasers, light emitting diodes and photovoltaic applications. In our case we are investigating the capabilities of photonic crystal slabs with the aim to improve the performance of heavy inorganic scintillators. To study the combination of scintillators and PhCs we use a Monte-Carlo program to simulate the light propagation inside a scintillator and a rigorous coupled wave analysis (RCWA) framework to analyse the optical PhC properties. The simulations show light output improvements of a wide range of scintillating materials due to light scattering effects of the PhC slabs. First samples have been produced on top of 1.2 × 2.6 × 5 mm LSO (cerium-doped Lutetium Oxyorthosilicate, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Lu</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SiO</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> : <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ce</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ) scintillators using electron beam lithography and reactive ion etching (RIE). Our samples show a 30-60% light output improvement when compared to unstructured reference crystals which is in close accordance with our simulation results. In addition, a theoretical investigation of the restrictions of the current PhC sample is given which concludes with prospects for improved future designs.

Preparation and characterization of Lu2SiO5:Ce3+ luminescent ceramic fibers via electrospinning

Abstract Cerium-doped lutetium oxyorthosilicate (Lu2SiO5:Ce3+, or shortly LSO:Ce) luminescent ceramic fibers were synthesized by the sol–gel process followed with electrospinning in the present research. Polyvinyl butyral (PVB) was used as a spinnable carrier and anhydrous system availed the efficient generation of the composite fibers. The phase of Lu2SiO5 starts to appear at 1100 °C based on XRD analysis. After annealed at 1200 °C for 4 h, all samples with different cerium doping concentrations show a pure phase of LSO with a well-crystallized structure. The annealed samples retain smooth surfaces and uniform morphologies. LSO:Ce fibers thus prepared exhibit a strong emission peak located at about 403 nm, corresponding to the Ce3+ 5d1→4 f1 transitions. LSO:1%Ce fibers exhibit the most intense emission among the samples doped with different cerium concentrations, which also present a much stronger emission than that of LSO:1%Ce powders. X-ray excited luminescence (XEL) spectrum shows that LSO:Ce fibers present a considerable scintillation property as well. Short decay time trait was also observed in LSO:Ce fibers due to their microscopic defects at grain boundaries and surfaces.

Improving of LSO(Ce) Scintillator Properties by Co-Doping

The influence of the co-doping of cerium-doped lutetium oxyorthosilicate (LSO) with ytterbium on the output characteristics of this scintillator material were investigated by studying X-ray luminescence spectra, emission decay kinetics, afterglow level, Vickers indentation hardness, thermally stimulated luminescence, and radiation stability of luminescence parameters. It has been demonstrated that the optimal doping contents are ~ 0.1 mol.% and ~ 0.5 mol.% for cerium and ytterbium, respectively. A considerable increase in the radiation stability of light output, decrease in the afterglow level by more than two orders of magnitude and a 20% decrease in indentation hardness at the optimal concentration of Yb have been observed, however, at the expense of the light output.

Multiple-Hit Parameter Estimation in Monolithic Detectors

We examine a maximum-a-posteriori method for estimating the primary interaction position of gamma rays with multiple interaction sites (hits) in a monolithic detector. In assessing the performance of a multiple-hit estimator over that of a conventional one-hit estimator, we consider a few different detector and readout configurations of a 50-mm-wide square cerium-doped lutetium oxyorthosilicate block. For this study, we use simulated data from SCOUT, a Monte-Carlo tool for photon tracking and modeling scintillation- camera output. With this tool, we determine estimate bias and variance for a multiple-hit estimator and compare these with similar metrics for a one-hit maximum-likelihood estimator, which assumes full energy deposition in one hit. We also examine the effect of event filtering on these metrics; for this purpose, we use a likelihood threshold to reject signals that are not likely to have been produced under the assumed likelihood model. Depending on detector design, we observe a 1%-12% improvement of intrinsic resolution for a 1-or-2-hit estimator as compared with a 1-hit estimator. We also observe improved differentiation of photopeak events using a 1-or-2-hit estimator as compared with the 1-hit estimator; more than 6% of photopeak events that were rejected by likelihood filtering for the 1-hit estimator were accurately identified as photopeak events and positioned without loss of resolution by a 1-or-2-hit estimator; for PET, this equates to at least a 12% improvement in coincidence-detection efficiency with likelihood filtering applied.

Air Atmosphere Annealing Effects on LSO:Ce Crystal

Cerium-doped lutetium oxyorthosilicate Lu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> :Ce crystal is a well-known scintillator with an excellent figure-of-merit. In this paper, air annealing was used to further improve its scintillation properties. The samples cut from Czochralski grown Lu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> :Ce crystals were annealed in air atmosphere at 1400°C for 10 h. Based on the analysis of the difference in the crystal's spectra (such as absorption, emission, and thermoluminescence) obtained before and after annealing, we investigate the nature of the observed effects. To investigate the annealing effects on the valence state of cerium ion, synchrotron radiation was used in this work as an energy source to measure the X-ray absorption near edge spectroscopy of cerium ions. It is supposed that annealing in air atmosphere helps to reduce the content of deep traps, which possibly include oxygen vacancy, lower the intensity of afterglow, shorten the decay time of afterglow, and increase the luminescence intensity of Ce2 (6-oxygen-coordinated). However, this may also cause cerium ion to be oxidized to +4 charge state, which may introduce an additional nonradiative trap center, thereby weakening luminescence.