Yttrium Gallium Research Articles

Optical investigations of coherence and relaxation dynamics of a thulium-doped yttrium gallium garnet crystal at sub-kelvin temperatures for optical quantum memory

Optical investigations of coherence and relaxation dynamics of a thulium-doped yttrium gallium garnet crystal at sub-kelvin temperatures for optical quantum memory

Evaluation of new scintillation crystals with MCDM methods for brain PET

Brain Positron Emission Tomography (PET) imaging has been increasingly important in recent decades for improved detection and staging of brain cancer and other brain illnesses. Many elements, including the choice of radiation detecting medium, contribute to the overall image quality used to characterize a PET system's performance. In our previous study, novel transparent optical scintillator crystals for brain PET system were simulated. Therefore, there is a need to evaluate these materials using advanced computational techniques. Hence, in this study, we evaluated and compared them using two Multi-Criteria Decision-Making (MCDM) techniques, namely Preference Ranking Organization Method for Enrichment Evaluations (PROMETHEE) and Visekriterijumska Optimizacija I Kompromisno Resenje (VIKOR). The crystals used in this study were strontium hafnate (SHO), gadolinium aluminum gallium garget (GAGG), gadolinium yttrium gallium aluminum garget (GYGAG), gadolinium lutetium gallium aluminum garget (GLuGAG), and lastly lutetium oxyorthosilicate (LSO) for comparison. Density, effective atomic number, energy resolution, light output, and decay time were selected as important criteria. Importance weights of each criteria were then assigned by considering the high resolution and high sensitivity detectors. With both MCDM methods, the results showed that SHO outranked the other scintillator materials followed by LSO and GLuGAG. GYGAG, and GAGG is revealed as the least favorable crystals, in agreement with the previous simulation studies. This study can be extended by including more scintillators as they become available in the future.

Growth, spectroscopy and laser operation of in-band pumped Ho3+-doped Yttrium Gallium Garnet

We report on the crystal growth of a 2.86 at.% Ho:YGG crystal, its structural and spectroscopic characterization, as well as on its first laser operation near 2.1 µm under in-band pumping by a Tm-fiber laser.

A new promising new choice for modern medical CT scanners: Cerium-doped gadolinium yttrium gallium aluminum garnet ceramic scintillator

Cerium-doped gadolinium yttrium gallium aluminum garnet (GYGAG) ceramics show great promise as scintillators for modern medical CT scanners. They exhibit exceptional scintillation efficiency, fast decay, low afterglow, and high X-ray stopping power. However, the performance of GYGAG ceramic scintillators in modern medical CT scanners has not been thoroughly investigated, as previous research has primarily focused on optimizing material performance. To address this research gap, we prepared a high-quality GYGAG ceramic scintillator and compared its performance to that of a widely used commercial GOS ceramic scintillator in medical CT scanners. The GYGAG scintillator showed comparable afterglow intensity, but significantly higher light yields and faster scintillation decay. Additionally, we developed two-dimensional GYGAG scintillator arrays integrated into a CT detector and assessed their spatial resolution and low-contrast detectability. The successful acquisition of CT images of an adult head phantom demonstrates the promising potential of GYGAG ceramic scintillators as alternatives for modern medical CT scanner detectors.

Quadratic Zeeman spectral diffusion of thulium ion population in an yttrium gallium garnet crystal

The creation of well understood structures using spectral hole burning is an important task in the use of technologies based on rare earth ion doped crystals. We apply a series of different techniques to model and improve the frequency dependent population change in the atomic level structure of Thulium Yttrium Gallium Garnet (Tm:YGG). In particular we demonstrate that at zero applied magnetic field, numerical solutions to frequency dependent three-level rate equations show good agreement with spectral hole burning results. This allows predicting spectral structures given a specific hole burning sequence, the underpinning spectroscopic material properties, and the relevant laser parameters. This enables us to largely eliminate power dependent hole broadening through the use of adiabatic hole-burning pulses. Though this system of rate equations shows good agreement at zero field, the addition of a magnetic field results in unexpected spectral diffusion proportional to the induced Tm ion magnetic dipole moment and average magnetic field strength, which, through the quadratic Zeeman effect, dominates the optical spectrum over long time scales. Our results allow optimization of the preparation process for spectral structures in a large variety of rare earth ion doped materials for quantum memories and other applications.

The effect of Ce concentration on the structural and optical properties of YGG:Ce phosphor

Y3(1-x) Ga5O12 phosphors doped with different Ce3+ concentration (with x = 0.005, 0.01, 0.02, 0.03, 0.04, 0.05) were prepared by sol-gel method. X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), scanning electron microscope (SEM), Infrared (IR) spectroscopy, photopluminescence (PL) and thermo-luminescence (TL) were used to characterize the phase structure and optical properties of the samples. XRD and XPS results reveal that the Ce3+ ions have entered into the YGG matrix and the lattice expansion is produced by the incorporation of Ce3+ ions. SEM analysis indicates the yttrium gallium garnet (YGG) phase has good quality, high purity and regular morphology after sintering at 1100 °C. IR spectrum analysis has confirmed the peaks with wave-numbers greater than 1000 cm−1are significantly reduced after sintering at 1100 °C. The results of TL glow curves show that three peaks with suitable trap depths exist in the phosphors and the maximum TL intensity of the phosphors is observed at x = 0.01. Optical absorption spectra obtained for the Ce3+doped YGG phosphors have illustrated the absorption bands at 298 and 424 nm are related to the Ce ions. The excitation and emission peaks of YGG:Ce phosphors are obtained at 443 and 522 nm respectively, corresponding to the 4f↔5d transition of Ce ions. The luminescence (both PL and TL) performance of phosphors strongly depend on the Ce3+ ions and YGG:Ce phosphor has the best luminescence performance when x = 0.01.

A Novel Synthetic Approach for the Preparation of Bulk Bi3Fe5O12 on the Y3Ga5O12 Core

In this study the bismuth iron garnet (Bi3Fe5O12; BIG) nanocrystals were obtained using non-thermodynamical approach. The hydrothermal synthesis of BIG was performed on the yttrium gallium garnet (Y3Ga5O12; YGG) substrate. For the hydrothermal synthesis of Y3Ga5O12 core the Ga2O3 and Y(NO3)3·6H2O starting materials were used. The final precursor solution was transferred to teflon container which was put inside the hydrothermal bomb and heated at 180 °C for 20 h. For the preparation of BIG shell on the YGG core the obtained Y3Ga5O12 particles were dispersed in distilled water using ultrasound, and then the citric acid, Bi(NO3)3·5H2O and Fe(NO3)3·9H2O were added under continuous stirring. Finally, the obtained solution was transferred to a teflon container which was put inside a hydrothermal bomb and heated at 180 °C for 20 h. The synthesis products were characterized by X-ray powder diffraction (XRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) with STEM module, and X-ray energy-dispersive spectroscopy (EDX) analysis. The obtained results clearly showed that the garnet Bi3Fe5O12 crystalline phase has formed.

Compositional screening of Ce-doped (Gd,Lu,Y)3(Al,Ga)5O12 ceramics prepared by quenching from melt and their luminescence properties

Quenching from the melt using an Optical Floating Zone furnace was investigated as a possible high-throughput preparation method in order to screen novel scintillating materials. To validate this method, polycrystalline rare-earth aluminum garnets and yttrium gallium aluminum garnets were synthesized and characterized by X-ray diffraction, photoluminescence and radioluminescence emission spectra as well as radioluminescence imaging and compared to the previously reported properties of those materials. In order to achieve rapid, but quantitative comparison of the materials, pellets fabricated from the synthesized powders were sintered; two different sintering conditions were investigated and compared. A simplistic energy deposition and light absorption model for brightness of opaque samples under X-ray irradiation was developed to estimate the relative scintillation efficiency of the materials. Based on the results, Y3Al5O12, LuY2Al5O12 and GdY2Al5O12 seem to have the highest scintillation efficiency among the prepared samples.

Rational Design of a Nd3+‐Mn4+ Co‐doped Luminescent Thermometer: Towards High‐Sensitivity Temperature Sensing

AbstractHigh temperature sensitivity is an important development direction for luminescent thermometers, especially in the physiological temperature range. Herein, neodymium(III) and manganese(IV) ions were co‐doped into a yttrium gallium garnet host (YGG) and the relevant dopant concentrations were optimized in detail. The temperature‐dependent spectral survey indicates that when the temperature was above 240 K, the 2Eg→4A2g transition of Mn4+ and the 4F5/2→4I9/2 emission of Nd3+ show strong fluorescence quenching and gradual fluorescence enhancement, respectively. Such an apparent contrast mainly originates from the nonradiative cross‐relaxation between 2Eg (or 4T2g) and 4A2g states of Mn4+ and thermal coupling between the 4F5/2 and 4F3/2 levels of Nd3+, respectively. The obvious difference in fluorescence between the two luminescent ions leads to an excellent temperature sensing performance. The obtained relative sensitivity shows a maximum value at 280 K (7.90 % K−1) and maintains a magnitude above 5.00 % K−1 over the whole physiological temperature range. Moreover, the related temperature uncertainties are below 0.1 K from 298 K to 323 K, and the repeatability capability is larger than 98 %. The findings in this study offer a feasible approach to promote the sensing capability of temperature sensors by rationally designing co‐doping systems.

Comparative study of structural, optical and magnetic properties of Er3+ doped yttrium gallium borates

The paper presents the results of a comprehensive study of yttrium gallium borate (YGa3(BO3)4) crystals low-doped (0.2 wt%) with erbium (Er3+) ions by in-situ X-ray diffraction (XRD), radioluminescence (RL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) techniques. Structural and elastic properties of YGa3(BO3)4: Er3+ crystals measured by the XRD method in the temperature range from 300 K to 1073 K have revealed the temperature variation of the volume thermal expansion coefficient. The analysis of RL spectra allowed us to assume the existence of the characteristic Er3+-related emission band located in the near-infrared region. The TSL spectra revealed strong peaks at low temperatures due to shallow traps and much less intense bands located above room temperature. Measurements of heat capacity in a wide temperature range allowed us to determine the Debye temperature θD ≈ 332 K. From the detailed analysis of the strongly anisotropic EPR spectra measured in YGa3(BO3)4:Er3+ crystals, the parameters of the spin Hamiltonian of Er3+ ions were determined: g⊥ = 9.34; g∥ = 1.269; A⊥ = 320.9 MHz; A∥ = 47.7 MHz. The temperature dependence of the spin-lattice relaxation rate of Er3+ ions was described well by the Orbach-Aminov process. It was proposed that Er3+ ions reside yttrium ions in YGa3(BO3)4 crystal lattice and are located in a slightly distorted prism made of six oxygen ions.

High-efficiency Er-doped yttrium gallium garnet laser resonantly pumped by a laser diode at 1.47 µm.

The spectroscopic and laser properties of an Er3+-doped yttrium gallium garnet crystal, Y3Ga5O12 (YGG), are studied. The stimulated emission cross section is 1.4×10-21cm2 at 1.65 µm. A continuous-wave laser resonantly pumped by a laser diode at 1.47 µm is demonstrated, delivering a maximum output power of 3.34 W. Benefiting from the low phonon energy of the YGG host, the corresponding slope efficiency is as high as ∼42%. To the best of our knowledge, this is the highest slope efficiency from the laser-diode resonantly pumped Er lasers at room temperature in the 1.6 µm spectral range.

Er3+/Ho3+ codoped nanogarnet as an optical FIR based thermometer for a wide range of high and low temperatures

In this work, a new strategy to increase the temperature working range of rare-earth based optical thermometers is demonstrated. Nanocrystalline yttrium gallium nanogarnets codoped with 0.1% Er3+ and 0.1% Ho3+ were synthesized. The codoped samples combine the high performance of erbium ions at high temperatures and that of holmium ions at low temperature, providing an overall relatively high sensor performance in a temperature range from 30 to 540 K, broader than that achievable by single Er3+ or Ho3+ doped nanogarnets. Measurements were carried out using 406 and 473 nm commercial diode lasers to excite the erbium and holmium ions, respectively. The emission spectra were analyzed as a function of temperature, using the fluorescence intensity ratio technique for each ion. Relative sensitivity and limit of detection were obtained in order to compare the efficiency of the sensor with optical thermometers reported up to date, capable of working in a similar range from cryogenic to high temperatures. The sensor presents a maximum relative sensitivity of about 1.3% K−1 at 200 K when exciting the erbium ions and around 0.4% K−1 at 200 K for the holmium ions. The limit of detection is under 0.5 K for most of the range from 30 K to 540 K using this combination of ions.

Exploring impurity phases derived from the introduction of vanadium ions in yttrium gallium garnet

The associated impurity phases derived from the introduction of vanadium ions in yttrium gallium garnet (YGG) were investigated in detail. The XRPD data indicate that β-Ga2O3 is contained in all synthesized samples and YVO4 can be identified when the V-doped concentration above 0.5 at. %. The existence of β-Ga2O3 is related to the antisite defects usually contained in the garnet host, and the generation of YVO4 is mainly derived from its lower formation temperature in comparison to the garnet phase. The micro-area composition analysis further verifies the existence of impurity phases, and the X-ray computed tomography survey provides a more visualized spatial distribution of the YVO4 phase. Moreover, the fluorescence analysis manifests a more sensitive phase identification than the XRPD technique, and the YVO4 impurity phase can be detected even if the V-doped content is reduced to 0.2 at. %. Additionally, the evaluated V/(V + Y + Ga) ratios from structure refinement coincide well with the theoretical value in the low-doping section, and the slight deviation in the high doping part is mainly attributed to the volatilization of vanadium oxides. What discussed in this study offers a comprehensive analysis strategy for the detection of impurity phases originating from ion doping.

A far‐red‐emitting (Gd,Y)3(Ga,Al)5O12:Mn2+ ceramic phosphor with enhanced thermal stability for plant cultivation

AbstractAs for plants, far‐red (FR) light with wavelength from 700 nm to 740 nm is critical for processes of photosynthesis and photomorphogenesis. Light‐controlled development depends on light to control cell differentiation, structural and functional changes, and finally converge into the formation of tissues and organs. Phosphor converted FR emission under LED excitation is a cost‐effective and high‐efficient way to provide artificial FR light source. With the aim to develop an efficient FR phosphor that can promote the plant growth, a series of gadolinium yttrium gallium garnet (GYGAG) transparent ceramic phosphors co‐doped with Mn2+ and Si4+ have been fabricated via chemical co‐precipitation method, followed sintered in O2 and hot isostatic pressing in this work. Under UV excitation, the phosphor exhibited two bright and broadband red emission spectra due to Mn2+: 4T1 → 6A1 spin‐forbidden transition, and one of which located in the right FR region. And then, Ce3+ ions were co‐doped as the activator to enhance the absorption at blue light region and the emission of Mn2+. It turns out that the emission band of GYGAG transparent ceramic phosphors matches well with the absorption band of phytochrome PFR, which means they are promising to be applied in plant cultivation light‐emitting diodes (LEDs) for modulating plant growth. Besides, the thermal stability of this material was investigated systematically, and an energy transferring model involves defects was also proposed to explain the phenomenon of abnormal temperature quenching.

Simulation of novel scintillator crystals for brain PET

In the last decade, different positron emission tomography (PET) crystals have been proposed for brain PET detectors. Brain PET cameras with restricted field of view to a smaller size to cover the brain can both exhibit significantly higher performance and lower the cost when compared to conventional whole-body PET scanners. The existing designs based on scintillation crystals employ the most commonly known materials such as lutetium oxyorthosilicate and bismuth germanate. This is due to their relatively good parameters such as high light yield and density. The main drawback of using scintillation crystals is that they have a modest energy resolution. In this study, a brain PET scanner was designed and simulated using a Geant4 Application for Tomographic Emission (GATE) toolkit. The performances of five crystals, namely strontium hafnate, gadolinium aluminium gallium garnet, gadolinium yttrium gallium aluminium garnet, gadolinium lutetium gallium aluminium garnet, and lutetium oxyorthosilicate for comparison, were evaluated in terms of sensitivity, spatial resolution, and count rate. The performance evaluation results showed that among the suggested scintillators, strontium hafnate can be considered as a promising alternative detector for high performance brain PET systems.

Mechanical properties and machinability of GYGAG:Ce ceramic scintillators

Cerium doped gadolinium yttrium gallium aluminum garnet ceramics, GYGAG:Ce for short, have drawn a lot of attention and showed a very promising application in medical CT detectors. This mainly attributes to their excellent scintillation properties, such as high light output, low afterglow, fast decay and high x-ray stopping power. In order to provide more accurate lesion location in real CT diagnosis, ceramic scintillators need to be machined into regular pixelated arrays, and the pixels should well match with the photodiode elements. Therefore, in addition to the scintillation characteristics, the mechanical properties and machinability of these ceramic scintillators should have been studied further, but such data and references are limited. In this research, we focused on the mechanical properties and the machinability behaviour of GYGAG:Ce ceramics. It was observed that GYGAG:Ce ceramics with grain size around 8 μm have the highest mechanical strength, and are highly suitable for machining process to achieve fine array pixels, for which a strict dimensional tolerance needs to be held.

High-efficiency 3 μm Er:YGG crystal lasers.

By balancing energy transfer and thermal effects, we demonstrate efficient erbium-doped yttrium gallium garnet (Er:YGG) crystal lasers at a wavelength of 2.82-2.92μm for the first time, to the best of our knowledge. Associated with the influence of doping concentration on energy transfer and thermal effects, the Er3+ doping concentration was optimized to be 10at.%, and with the optimized crystal, the maximum continuous-wave output power was 1.38W, corresponding to the slope efficiency of 35.4% approaching the theoretical quantum limits. The thermal effects during the laser process were discussed. We believe that this work should be helpful for optimizing the erbium-doped gain for the 3μm laser and the development of 3μm lasers.

Transparent Ceramic Garnet Gamma-Ray Spectrometer With Directionality

We have developed a handheld $\gamma $ -ray spectrometer based on 1024 pixels, $2.8\,\,\text {mm} \times 2.8\,\,\text {mm} \times 6$ mm in size, of gadolinium–yttrium–gallium–aluminum garnet (GYGAG) ((Gd,Y,Ce)3(Ga,Al)5O12) ceramic scintillator (total of 48-cm3 detector volume) coupled to silicon photodiode (SiPD) arrays. The SiPD arrays and readout ASIC, originally developed for medical imaging applications, have been adapted for portability in a lightweight box with heatsink and thermoelectric cooling. Custom readout firmware for $\gamma $ -ray spectroscopy has been implemented, and a system user interface was developed that runs on an Android tablet. We have optimized the processing of the GYGAG(Ce), the pixel optical coupling, and electronics readout parameters to obtain single pixel energy resolution as good as $R (662\,\,\text {keV}) = 3.1$ % full-width at half-maximum and full device resolution with singles events from all pixels summed of 4.5%. When Compton-summed events are included, full-energy peak efficiency increases by $\sim 2\times $ , and $R (662\,\,\text {keV}) = 4.7$ % is obtained for the full device. The pixelated architecture is leveraged to locate point sources of radiological materials using Compton imaging and active masking techniques. Directional detection of a 1 mCi Cs-137 source at 10 m can be made to ±10° in ~2 s.

Synthesis, structure interpretation, antimicrobial and anticancer studies of tranexamic acid complexes towards Ga(III), W(VI), Y(III) and Si(IV) metal ions

A new four tranexamic acid (TXA) complexes of some transition metal ions yttrium(III), tungsten(VI), and non-transition metal ion gallium(III) and silicon(IV) have been prepared. The TXA synthesized complexes have been characterized by molar conductance, magnetic susceptibility, infrared, electronic spectral, 1HNMR, thermal analyses, X-ray diffraction patterns, scanning and transmittance electron microscopies, and elemental microanalysis (C, H, N, and Cl). The study shows that these complexes have octahedral geometry with the formulas [Ga(TXA)2(Cl)3(H2O)], [Si(TXA)2(Cl)4], [W(TXA)2(Cl)2]·Cl2 and [Y(TXA)2(Cl)(H2O)]·4H2O. Tranexamic acid complexes were formed in 1:2 (metal: ligand) stoichiometry. Based on the reported results, it may be concluded that in case of transition metal ions (tungsten(VI) and yttrium(III)) the deprotonated ligand (TXA) to tranexamate ion coordinated to metal –COO carboxylate ions as bidentate ligand through the oxygen atom of the carboxylate group and the nitrogen atom of the amino group –NH2, where the TXA ligand coordinated as a monodentate through the nitrogen atom of –NH2 group in case of non-transition metal ions. The metal complexes have been screened for their in microbiological activities against some kind of bacteria (G+ & G−) and fungi. For instance, in vitro anti-cancer activity of the gallium(III) complex was screened against the human hepato cellular carcinoma (HepG-2) tumor cell line.

Pulsed laser deposition of crystalline garnet waveguides at a growth rate of 20 μm per hour

We report pulsed laser deposition of high-quality crystalline yttrium aluminium oxide and yttrium gallium oxide with a growth rate approaching 20μm per hour by using an excimer laser operating at a repetition rate of 100Hz. This result demonstrates the capability of PLD at 100Hz for upscaling deposition speeds to a rate that is industrially relevant. In addition, we show that use of this high repetition rate can cause additional heating of the substrate, which in turn affects the film composition. This effect is used as an additional control parameter on the composition, and thus refractive index, of the grown material.