Multicomponent Garnets Research Articles

Temperature dependence of photoluminescence kinetics, scintillation properties, and coincidence time resolution of Mo co-doped Y1.5Gd1.5Al2Ga3O12:Ce (Mo = 0, 300, 600 ppm) multicomponent garnet crystals

Temperature dependence of photoluminescence kinetics, scintillation properties, and coincidence time resolution of Mo co-doped Y1.5Gd1.5Al2Ga3O12:Ce (Mo = 0, 300, 600 ppm) multicomponent garnet crystals

Mössbauer and magnetization measurements of multicomponent iron garnets

Four Gd-containing iron garnets were investigated using Mössbauer spectroscopy and Vibrating Sample Magnetometry over a wide temperature range, from 4K to ∼600K. The magnetic ordering temperature and hyperfine parameters determined on the basis of Mössbauer spectra for all samples were found to be surprisingly similar, differences were only noted for the average magnetic moments, which turned out to be strongly correlated with the magnetic moments of rare earth elements present in the structure. Further differences between the systems were also highlighted in measurements in the external 9T magnetic field, especially around the compensation temperature. Changes in the nature of the Mössbauer spectra were interpreted based on the crystal field approximation confirming the correctness of the interpretation of the temperature dependence of magnetization for these samples.

Synthesis and Luminescent Properties of Multicomponent Garnets Y3MgGa3SiO12, Y3MgGa2AlSiO12, and Y3MgGaAl2SiO12 Doped with Cr3+ Ions

Ceramic samples of Y3MgGa3SiO12, Y3MgGa2AlSiO12, and Y3MgGaAl2SiO12 multicomponent garnets doped with 0.2 at % Cr3+ have been obtained by high-temperature solid-state synthesis. In the luminescence spectra of the synthesized garnet samples, overlapping broadband luminescence is observed in the far red spectral region caused by the 4T2 → 4A2 transition in Cr3+ ions, and a narrow band is observed in the range of 690–700 nm, corresponding to the zero-phonon line of the 2Е → 4A2 transition in Cr3+. The narrow-band and broad-band parts of the spectra are attributed to radiation from two different types of chromium centers, which are in octahedral coordination with different distortion degrees and strength of the crystal field. This results from the presence of two ions at the octahedral position of these garnets, which differ significantly in crystal chemical properties, namely, Mg2+ and Ga3+ (Al3+). The studied phosphors, which have broadband luminescence in the phytoactive far red region of the spectrum, have the potential for use in greenhouse LED lamps.

Magnetization measurements of multicomponent iron garnets

Magnetization studies were performed on four Gd-containing iron garnets. Measurements have been done in an external constant magnetic field as a function of temperature. A change in the orientation of magnetization was observed at the compensation temperature in measurements without an external magnetic field, and ranges of no dependence of magnetization on temperature around the compensation temperature in measurements in strong magnetic fields up to 9 T. The results were interpreted using crystal field approximation, and on this basis the magnetic moments of the particular elements as well as molecular field coefficients λij were determined.

Bulk Single-Crystal Growth of Ce/Gd3(Al,Ga)5O12 from Melt without a Precious Metal Crucible by Pulling from a Cold Container

We report the growth of cerium-doped multicomponent garnet (Ce/GAGG) single crystals based on crystal pulling from a melt using a cold container without employing a precious metal crucible. This novel method is described in detail. We measured the optical, luminescence, and scintillation characteristics of several samples cut from three crystals and compared them with a commercial Ce/GAGG crystal. The best samples from the set are fully comparable in all characteristics with the commercial reference crystal, demonstrating the practical potential of this method. Avoidance of an expensive precious metal crucible in this method makes crystal growth much more economical.

Scintillation Characteristics of the Single-Crystalline Film and Composite Film-Crystal Scintillators Based on the Ce3+-Doped (Lu,Gd)3(Ga,Al)5O12 Mixed Garnets under Alpha and Beta Particles, and Gamma Ray Excitations.

The crystals of (Lu,Gd)3(Ga,Al)5O12 multicomponent garnets with high density ρ and effective atomic number Zeff are characterized by high scintillation efficiency and a light yield value up to 50,000 ph/MeV. During recent years, single-crystalline films and composite film/crystal scintillators were developed on the basis of these multicomponent garnets. These film/crystal composites are potentially applicable for particle identification by pulse shape discrimination due to the fact that α-particles excite only the film response, γ-radiation excites only the substrate response, and β-particles excite both to some extent. Here, we present new results regarding scintillating properties of selected (Lu,Gd)3(Ga,Al)5O12:Ce single-crystalline films under excitation by alpha and beta particles and gamma ray photons. We conclude that some of studied compositions are indeed suitable for testing in the proposed application, most notably Lu1.5Gd1.5Al3Ga2O12:Ce film on the GAGG:Ce substrate, exhibiting an α-particle-excited light yield of 1790-2720 ph/MeV and significantly different decay curves excited by α- and γ-radiation.

Optical and scintillation characteristics of Lu2Y(Al5-xGax)O12:Ce,Mg multicomponent garnet crystals

Optical and scintillation characteristics of Mg2+-codoped Lu2Y(Al5-xGax)O12:Ce (x = 2, 3) multicomponent garnet crystals grown by the micro-pulling down method were investigated. At RT, the shortening of scintillation decay time and a decrease of light yield (LY) value measured for a higher Ga containing samples can be explained by thermal ionization of the Ce3+ 5d1 excited state. At 662 keV γ-rays, Lu2YAl3Ga2O12: Ce, 0.05%Mg exhibits high LY value of 29,000 ph/MeV along with scintillation decay times of 50 ns (86%) + 73 ns (14%). Co-doping with larger Mg2+ content leads to a decrease of LY value, scintillation decay time, and afterglow level. Radioluminescence quenching observed at low temperature region in correlation with large thermoluminescence peaks can be caused by trapping of electrons at intrinsic shallow traps.

Effects of composition and growth parameters on phase formation in multicomponent aluminum garnet crystals.

The effects of composition on the phase formation of multicomponent garnet crystals grown via directional solidification by the micro-pulling-down method are studied. A relatively wide range of rare-earth (RE) average ionic radii (AIR) is explored by formulating ten compositions from the system (Lu,Y,Ho,Dy,Tb,Gd)3Al5O12. Crystals were grown at either 0.05 or 0.20 mm min-1. The hypothesis is that multicomponent compounds with large AIR will form secondary phases as the single-RE aluminum garnets formed by larger Tb3+ or Gd3+; this will result in crystals of poor optical quality. Crystals with large AIR have a central opaque region in optical microscopy images, which is responsible for their reduced transparency compared to crystals with small AIR. Slow pulling rates suppress the formation of the opaque region in crystals with intermediate AIR. Powder and single-crystal X-ray diffraction and electron probe microanalysis results indicate that the opaque region is a perovskite phase. Scanning electron microscopy and energy dispersive spectroscopy measurements reveal eutectic inclusions at the outer surface of the crystals. The concentration of the eutectic inclusions increases with increasing AIR.

Crystal chemistry of rare-earth containing garnets: Prospects for high configurational entropy

Materials with high degrees of lattice configurational entropy are being studied to assess their potential as highly-stable materials with potentially new and unusual properties. This report involves an assessment of the prospects for producing novel, complex multi-component oxide compounds that have the garnet crystal structure. We examine the crystal chemistry of garnets in an effort to determine if it may be possible to design so-called “high-entropy oxide” garnets, i.e., garnets containing numerous cation components, such that the compounds are stable, monophasic, and offer the potential for new and unusual physical properties. In this report, we quantify configurational entropy for compounds such as garnet that possess numerous cation sublattices. Then, we consider coordination polyhedra and details of bonding in rare-earth containing garnets, in an effort to predict structural aspects of multi-component oxide garnets.

Compositional engineering of multicomponent garnet scintillators: towards an ultra-accelerated scintillation response

A Czochralski-grown single crystal of GAGG:Ce,Mg allows for a high Ce dopant and Mg codopant concentration in the crystal, resulting in acceleration of scintillation decay down to several nanoseconds at the expense of light yield.

Luminescence and scintillation properties of Mo co-doped Y0.8Gd2.2(Al5-xGax)O12: Ce multicomponent garnet crystals

Mo co-doped Y0.8Gd2.2(Al5-xGax)O12:Ce (x = 2.6 and 3) multicomponent garnet crystals were grown by the micro-pulling down method and the luminescence and scintillation properties were investigated. The temperature dependences of radioluminescence yield and photoluminescence decay time were measured to investigate the temperature stability of these crystals. Under excitation with 662 keV γ rays at room temperature, Y0.8Gd2.2(Al2.4Ga2.6)O12:Ce,Mo shows a higher light yield of 53,800 ph/MeV whereas Y0.8Gd2.2(Al2Ga3)O12:Ce,Mo shows a faster scintillation decay times of 50 ns (56%) + 275 ns (44%). A decrease of radioluminescence yield at low temperature observed in correlation with an appearance of the large thermoluminescence peaks can be attributed to the localization of charge carriers at shallow traps.

Czochralski growth and characterization of the multicomponent garnet (Lu1/4Yb1/4Y1/4Gd1/4)3Al5O12

This work demonstrates the potential for practical scalable growth of complex garnets and evaluates the implications of a multicomponent composition in the optical quality and elemental distribution of a Czochralski-grown crystal. Our experimental approach was designed to elucidate the relation between a complex garnet composition ${({\mathrm{Lu}}_{1/4}{\mathrm{Yb}}_{1/4}{\mathrm{Y}}_{1/4}{\mathrm{Gd}}_{1/4})}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12}$, crystal growth parameters, crystal structural, and elemental homogeneity. Our hypothesis is that combining multiple rare earths (REs) that will fractionally occupy the dodecahedral site in the aluminum garnet structure will result in a stable, single garnet compound that can be grown by the Czochralski method. Single-crystal and powder x-ray diffraction indicated a single garnet phase with an increasing unit cell volume from seed to tail. In addition, we propose that the pattern of elemental segregation will be based on the deviation of the ionic radius of each constituent RE from the average RE ionic radius of the multicomponent garnet. Electron probe microanalysis revealed that ions that are smaller than that average (${\mathrm{Lu}}^{3+}$ and ${\mathrm{Yb}}^{3+}$) are preferentially incorporated in the crystal, while elements that are larger than that average (${\mathrm{Gd}}^{3+}$) are rejected. The ionic radius of ${\mathrm{Y}}^{3+}$ is close to that average and yttrium segregation was minimal. The concentrations of the four REs are closer to stoichiometric on the tail end of the boule. Scanning electron microscopy and energy-dispersive x-ray spectroscopy analysis reveal Gd-rich inclusions with eutectic microstructures in the tail end of the boule.

High-pressure and high-temperature single-crystal X-ray diffraction of complex garnet solid solutions up to 16\xa0GPa and 823\xa0K

P–V–T equations of state (EoS) of synthetic garnet solid solutions with ternary grossular–almandine–pyrope compositions relevant to the Earth’s upper mantle have been determined in order to examine whether garnet properties can be accurately interpolated from those of the end-members. Volumes have been measured as a function of pressure using single-crystal X-ray diffraction measurements performed inside a diamond anvil cell. Isothermal bulk moduli and first pressure derivatives were obtained by fitting the P–V data using a third-order Birch–Murnaghan equation of state. Two nominally eclogitic garnets (Prp47Alm19Grs31And3 and Prp53Alm19Grs18And3Sps7) were found to have isothermal bulk moduli (KT0) and pressure derivatives (K′T0) of 170(3) GPa, 4.1 (4) and 173 (2) GPa, 3.8 (5), respectively. KT0 and K′T0 for an almandine-rich garnet (Prp26Alm63Grs6And5) were found to be 175 (3) GPa and 3.7 (7), respectively. High-temperature compression experiments at 703 K and 823 K were carried out on sample Prp47Alm19Grs31And3, resulting in the high-temperature EoS term (∂KT/∂T)P = − 0.025 (6) and a thermal expansion (α0) of 2.86 (4) × 10−5 K−1. The results imply that the bulk moduli of aluminous garnet solid solutions stable at upper mantle conditions can be deduced from the properties of the end-members with minimal uncertainty. We show that the difference in the bulk sound velocity determined for a multicomponent eclogitic garnet composition and obtained for the same composition from the end-member properties is better than 0.5% for pressures and temperatures corresponding to Earth’s upper mantle.

Профильный анализ пленок ферритов-гранатов методом оптической эмиссионной спектроскопии тлеющего разряда

Annotation.The paper presents the results of experiments on the application of the method of optical emission spectroscopy of a glow discharge for the profile analysis of vacuum-deposited single and two-layer films of multicomponent garnet ferrites of various compositions before and after crystallization annealing. The presence of internal and external transition layers was revealed, and the modification of their elemental composition during crystallization, as well as the different sequence of synthesis of individual components in ferrite-garnet heterostructures, was investigated.

Crystal Growth and Elemental Homogeneity of the Multicomponent Rare-Earth Garnet (Lu1/6Y1/6Ho1/6Dy1/6Tb1/6Gd1/6)3Al5O12

High-entropy aluminum garnets were grown as bulk single crystals using the micro-pulling-down method, taking the synthesis of complex ceramics a step further from the conventional preparation of polycrystalline materials. We studied the effects of growth parameters on the elemental distribution in high optical quality crystals of (Lu1/6Y1/6Ho1/6Dy1/6Tb1/6Gd1/6)3Al5O12 containing six cations (yttrium and rare-earths) taken in equimolar amounts. A single garnet structure was confirmed by powder X-ray diffraction. Electron microprobe measurements were obtained to correlate the radial distribution of rare-earth elements with pulling rates and molten zone height. The nature of the elemental distribution in the radial direction was associated with ionic radius: smaller rare-earths concentrated in the center of the crystal, while larger rare-earths segregated toward the outer edge of the cylindrical crystal. Faster pulling rates led to a flattening of the concentration profiles toward the nominal concentration, promoting a more homogeneous radial elemental distribution, while varying the molten zone height did not have a significant effect. The demonstrated success with crystal growth enables the practical availability of single crystals of multicomponent aluminum garnets for further discovery of new phenomena and applications.

Luminescent, Scintillation, and Photoconversion Properties of Micro‐Pulling‐Down‐Grown Single Crystals of Ce3+‐Doped Gd3−xLuxAl5−yGayO12 Garnets

Herein, the development of phosphor‐converted white light‐emitting diodes (pc‐WLED) and scintillators based on the crystals of Ce3+‐doped multicomponent garnets, grown by the micro‐pulling‐down (MPD) method is studied. The combined technique of the “bandgap engineering” and “positioning of Ce3+ 5d‐levels” is applied to the crystals of Gd3−xLuxAl5−yGayO12 (x = 0–1.5 and y = 2–3) mixed garnets for improving their color‐rending properties in pc‐WLEDs application as well as their scintillation figure of merit. The absorption, cathodoluminescence, photoluminescence, photoconversion (PC), and also the scintillation light yield and scintillation decay time measurements under excitation by α‐particles of 239Pu radioisotope are used for the characterization of the crystals. Among all the investigated garnet compounds, the best photoconverting properties are observed in Gd3−1.5Lu0−1.5Al5−yGayO12:Ce crystals at x = 0–1.5 and y = 2.5–3. Meanwhile, the best scintillation characteristics are found in Gd3−xLuxAl5−yGayO12 crystals at x = 0–1.5 and y = 2–2.5.

Spectral Properties and Thermal Quenching of Mn4+ Luminescence in Silicate Garnet Hosts CaY2MgMAlSi2O12 (M = Al, Ga, Sc)

Multi-component silicate garnet ceramics CaY2MgMAlSi2O12 comprising different cations M = Al, Ga or Sc in octahedral sites doped with Mn4+ ions have been synthesized and studied as novel red-emitting phosphors aiming at warm white pc-LED applications. All synthesized phosphors exhibit Mn4+ luminescence in rather deep red region, the shortest-wavelength spectrum of Mn4+ luminescence (peak wavelength at 668 nm) being obtained for the host with the largest cation M3+ = Sc3+ in the octahedral site. The effect of increasing the energy of the emitting Mn4+2E level with the size of the host cation in octahedral sites is supposed to be the result of decrease of the covalence of the “Mn4+-ligand” bonding with increase of the interionic Mn4+–O2– distance. All studied phosphors demonstrate rather poor thermal stability of Mn4+ photoluminescence with a thermal quenching temperature T1/2 below 200 K, the lowest value being observed for the host with M = Sc. As expected, the decrease of the energy of the O2––Mn4+ charge-transfer state is observed with the increase of the M3+ cation radius, i.e. with the increase of the O2––Mn4+ interionic distance. The thermal quenching temperature of Mn4+ luminescence in the studied phosphors correlates with the energy of the O2––Mn4+ charge transfer state which is supposed to serve as a quenching state for Mn4+ luminescence.

Fabrication and Optical Properties of 2at.%Yb:LuYAG Mixed Crystal through Nanocrystalline Powders

Ytterbium doped Lu1.5Y1.5Al5O12 (LuYAG) nanocrystalline powders were synthesized by a wet chemical mixed precipitant co-precipitation (MPP) method, and then the mixed crystal of Yb:LuYAG was grown in an optical floating zone (OFZ) furnace at the speed of 6–10 mm/h, using a [111] oriented YAG seed crystal. The transmittance of the polished LuYAG crystal is close to the ideal value of LuAG or YAG. The X-ray rocking curve shows complete symmetry and the full width at half maximum (FWHM) is 10 arc-second, indicating the good quality of as grown Yb:LuYAG multicomponent garnet crystal. The thermal luminescent spectrum at room temperature shows four deep energy traps at around 1–1.3 eV. X-ray excited luminesce (XEL) spectra is measured to characterize the existence of LuAl or YAl shadow defects in the bulk single crystal. The emission peak at around 320 nm indicates that the LuYAG crystal prepared by OFZ have lower concentrations of antisite defects (AD) with respect to its Czochralski counterpart.

Gallium preference for the occupation of tetrahedral sites in Lu3(Al5-xGax)O12 multicomponent garnet scintillators according to solid-state nuclear magnetic resonance and density functional theory calculations

In this study, the distributions of aluminum and gallium atoms over the tetrahedral and octahedral sites in the garnet structure were investigated in mixed Lu3Al5-xGaxO12 crystals by using 27Al and 71Ga magic angle spinning nuclear magnetic resonance (NMR) and single crystal 71Ga NMR. The experimental study was supported by theoretical calculations based on density functional theory (DFT) in order to predict the trends in terms of the substitutions of Al by Ga in the mixed garnets. Both the experimental and theoretical results indicated the non-uniform distribution of Al and Ga over the tetrahedral and octahedral sites in the garnet structure, with a strong preference for Ga occupying the tetrahedral sites in the garnet structure at all Ga concentrations, despite Ga having a larger ionic radius than Al and tetrahedrons being smaller than octahedrons. The Ga occupation preference is primarily related to the involvement of Ga 3d10 electrons in interactions, and due to the different nature of the chemical bonds formed by Al and Ga when located in the tetrahedral and octahedral environments. The quadrupole coupling constants and chemical shift parameters for Al and Ga nuclei were determined for all of the compounds considered, and the electric field gradients at the Al and Ga nuclei were calculated in the DFT framework. Our results also showed that the structural relaxation after Al substitution with the larger Ga mainly occurs via deformation of the octahedrons, while leaving the tetrahedrons relatively undeformed.

Photoinduced Preparation of Bandgap-Engineered Garnet Powders

The indirect photochemical synthesis for the preparation of bandgap- or defect-engineered multicomponent garnet powders from aqueous solutions was investigated. Gd3(Ga,Al)5O12 (GGAG) doped with Ce or Ce + Eu and Lu3(Al,Sb)5O12 doped with Eu were produced by calcination of the prepared solid precursors at various conditions and their structural and luminescence properties including decay curves were thoroughly studied. In GGAG:Ce, the content of Ga was shown to have strong impact on the lattice parameter and position of the Ce3+ 5 d - $4f$ emission. To induce the formation of Ce4+ ions as defects competing with electron traps, Mg2+ ions were added into the solutions and calcination in air was examined. Both factors were shown to cause the decrease of Ce3+ emission intensity and acceleration of luminescence decay in a similar way. The doping with Sb(III) required calcination of solid precursors in inert atmosphere to prevent formation of an unknown pyrochlore-type phase containing Sb(V). Low temperatures were needed to limit Sb2O3 evaporation during calcination.