Garnet Host Research Articles

Red emission enhancement in Ce3+/Mn2+ co-doping suited garnet host MgY2Al4SiO12 for tunable warm white LED

To enhance the red emission of YAG:Ce3+ system, co-doping a second activator is one of the attractive approaches and Mn2+ is a priority candidate for red emission. However, the doping of Mn2+ in YAG will result in the multi-occupancy in different crystallographic sites, due to the mismatch of crystal radius and charge. Thus, a suited aluminate silicate garnet phosphor host MgY2Al4SiO12 with ideal crystallographic sites for the co-doping of Ce3+ and Mn2+ ions, was adopted to be the host. The local coordination of Mn2+ ions, occupying only the dodecahedral Mg2+ sites in our suited garnet phosphor, was confirmed by XRD, XPS and photoluminescence results. A color tunable emission of the Ce3+/Mn2+ co-doping phosphor MgY2Al4SiO12 can be realized by combining the yellow emission (565 nm) originating from Ce3+ with the red emission (620 nm) from Mn2+, under 460 nm excitation. The energy transfer efficiency from Ce3+ to Mn2+ via adipole-quadrupole mechanism was demonstrated to be high and reach 79.7%, which is quite higher than 45% in YAG:Ce3+,Mn2+,Si4+. More importantly, the enhancement of red emission makes the emitting colors be able to be adjusted from yellow to orange-red, which would be beneficial to the colorpoint tuning of WLED. The excellent photoluminescence characterizes with high quantum yields (up to 89.0%) indicates that the designed MgY2Al4SiO12:Ce3+,Mn2+ phosphor is a good candidate to obtain warm white LED.

Synthesis and luminescent properties of prospective Ce3+ doped silicate garnet phosphors for white LED converters

The results on crystallization and investigation of the luminescent properties of prospective ceramic phosphors based on the Ce3+ doped {Ca2R}[ScB](CSi2)O12 (R = Lu, Y, Gd; B = Sc, Ga, C = Ga, Al) silicate garnets are presented for the first time in this work. We have observed the variations of the spectroscopic properties of Ce3+ ions in the mentioned Ca2+-Si4+ garnet hosts depending on the cation content at the dodecahedral {}, octahedral [] and tetrahedral () sites of garnet lattice. These results can be useful for the development of new generation of ceramic phosphor converters for white LEDs based on the garnet compounds under study.

Graphite‐bearing mineral assemblages in the mantle beneath Central Aldan superterrane of North Asian craton: combined confocal micro‐Raman and electron microprobe characterization

Mantle‐derived lherzolitic and harzburgitic Cr‐pyropes from lamprophyres of the Chompolo field (Central Aldan superterrane, North Asian Craton) were studied using micro‐Raman spectroscopy and electron microprobe microanalysis. These garnets enclose graphite coexisting with forsterite, diopside, Ba‐Cl‐phlogopite, tschermakite, rutile, magnesiochromite, Mg‐ilmenite, apatite, chalcopyrite, dolomite, magnesite and lindsleyite inclusions. The PT conditions of residence of graphite‐bearing assemblage in the mantle were estimated, using a combination of mineral thermometers and barometers, to be as high as 2.87–3.55 GPa and 710–770 °C. Generally, graphite within inclusions is well ordered; D1 and D2 disordered bands in its spectra are restricted to inclusion edges. The residual pressure up to 2.1 GPa was inferred for graphite assuming pressure dependence of the G‐band upshift (1580 cm−1 at ambient conditions vs 1588.6 cm−1 at 2.1 GPa). Disordered graphite most likely appears due to the stress‐induced distortion of the fully ordered graphite crystal structure. The distortion results from difference in the thermoelastic properties of graphite inclusions and their garnet hosts exposed to decompression during ascent to the surface with lamprophyre magma. The mineralogy of inclusions in the studied garnets strongly suggests an episode(s) of metasomatism by carbon‐rich agent(s) (COH‐fluid or carbonatitic melt) in the lithospheric mantle of the Central Aldan superterrane, which was coeval with the formation of graphite inclusions and the host pyropes. Copyright © 2017 John Wiley & Sons, Ltd.

Luminescence and energy transfer processes in Ce3+ activated (Gd,Tb)3Al5O12 single crystalline films

The luminescence and scintillation properties of gadolinium terbium aluminium garnet single crystalline films, Gd3−xTbxAl5O12, doped with Ce3+ are investigated as a function of the Gd/Tb ratio with the aim of an improved understanding of the energy transfer processes between Ce3+ and Tb3+ ions in the aluminium garnet hosts. Upon replacing the Gd3+ by Tb3+, the crystal field splitting for the 5d energy level of Ce3+ does not change significantly, due to comparable sizes of the Gd3+ and Tb3+ cations. Temperature dependence of the decay time of Tb3+ and Ce3+ luminescence confirms an efficient energy transfer from the Tb3+ to Ce3+ and provides a qualitative understanding of this process. Furthermore, bidirectional energy transfer processes between the Ce3+ and Tb3+ are revealed. Scintillation decays under α-particles excitation show the presence of the fast and slow sub-microsecond components.

The redox budget of crust-derived fluid phases at the slab-mantle interface

The redox processes taking place in the portion of the mantle on top of the subducting slab are poorly investigated and the redox potential of crust-derived fluid phases is still poorly constrained. A case study of supra-subduction mantle affected by metasomatism from crust-derived fluid phases is represented by garnet orthopyroxenites from the Maowu Ultramafic Complex (China) deriving from harzburgite precursors metasomatised at ∼4GPa, 750–800°C by a silica- and incompatible trace element-rich fluid phase. This metasomatism produced poikilitic orthopyroxene and inclusion-rich garnet porphyroblasts. Solid multiphase primary micro-inclusions in garnet display negative crystal shapes and infilling minerals (spinel, ±orthopyroxene, amphiboles, chlorite, ±talc, ±mica) occur with constant modal proportions, indicating that they derive from trapped solute-rich aqueous fluids. FT-IR hyper spectral imaging analyses and Raman spectroscopy, together with X-ray microtomography performed on single inclusions indicate that liquid water is still preserved at least in some inclusions (±spinel).To investigate the redox budget of these fluid phases, we measured for the first time the Fe3+ concentration of the micron-sized precipitates of the multiphase inclusions using EELS on a TEM. Results indicate that spinel contains up to 12% of Fe3+ with respect to the total iron, amphibole about 30%, while the ratio in inclusion phases such as chlorite and phlogopite may reach 70%. The Fe3+ fraction of the host garnet is equal to that measured in spinel as also confirmed by Flank Method EPMA measurements.Forward modelling fO2 calculations indicate that the garnet orthopyroxenites record ΔFMQ=−1.8÷−1.5, therefore resulting apparently more reduced with respect to metasomatised supra-subduction garnet-peridotites. On the other hand, oxygen mass balance, performed both on the Maowu hybrid orthopyroxenite and on metasomatised supra-subduction garnet peridotites, indicate that the excess of oxygen (nO2) is the same (10molm−3). The oxygen mass balance of the crust-derived fluids (multiphase inclusions) also indicates that the fluid precipitates are more oxidised than the host rock, reaching up to 400molm−3 of nO2. This suggests that even after their interaction with the metasomatic orthopyroxenites, the residual fluid phases could be potentially carrier of oxidised components when it escapes the slab-mantle interface. Because of this gradient in nO2, a metasomatic front develops from the oxidised slab to the overlying lithospheric mantle wedge passing through a transitional layer of hybrid rocks at the slab-mantle interface.

Recovery of an oxidized majorite inclusion from Earth's deep asthenosphere.

Minerals recovered from the deep mantle provide a rare glimpse into deep Earth processes. We report the first discovery of ferric iron-rich majoritic garnet found as inclusions in a host garnet within an eclogite xenolith originating in the deep mantle. The composition of the host garnet indicates an ultrahigh-pressure metamorphic origin, probably at a depth of ~200 km. More importantly, the ferric iron-rich majoritic garnet inclusions show a much deeper origin, at least at a depth of 380 km. The majoritic nature of the inclusions is confirmed by mineral chemistry, x-ray diffraction, and Raman spectroscopy, and their depth of origin is constrained by a new experimental calibration. The unique relationship between the majoritic inclusions and their host garnet has important implications for mantle dynamics within the deep asthenosphere. The high ferric iron content of the inclusions provides insights into the oxidation state of the deep upper mantle.

Temperature dependence of CIE-x,y color coordinates in YAG:Ce single crystal phosphor

Using single-crystal YAG:Ce plates with different dopant concentration under different sample temperatures (77-500(800)K), absorption, emission and luminescence decay characteristics were measured. Simulation is used to explain the luminescence decay time increase with growing temperature. For selected incident blue excitation band and given sample thickness the composed blue-yellow spectrum is calculated after passing through the sample. Temperature dependence of the color coordinates CIE-xy is calculated, arising mostly due to specific temperature dependence of the 4f-5d1 absorption transition of Ce3+ center in the garnet host.

Oxygen isotope thermometry using quartz inclusions in garnet

AbstractOxygen isotope ratios of quartz inclusions (QI) within garnet from granulite and amphibolite facies gneisses in the Adirondack Mountains, NY were analysed and used to determine metamorphic temperatures. Primary QI for eight of 12 samples have δ18O values significantly lower than matrix quartz (MQ). The primary QI retain δ18O values representative of thermal conditions during garnet crystallization, whereas the δ18O values of MQ were raised by diffusive exchange with other matrix minerals (e.g. mica and feldspar) during cooling. The δ18O differences between QI and MQ show that garnet (a mineral with slow diffusion of oxygen) can armour QI from isotopic exchange with surrounding matrix, even during slow cooling. These differences between δ18O in MQ and QI can further be used to test cooling rates by Fast Grain Boundary diffusion modelling. Criteria for identifying QI that preserve primary compositions and are suitable for thermometry were developed based on comparative tests. Relations between δ18O and inclusion size, distance of inclusion to host–garnet rim, core–rim zonation of individual inclusions, and presence or absence of petrological features (healed cracks in QI, inclusions in contact with garnet cracks lined by secondary minerals, and secondary minerals along the inclusion grain boundary) were investigated. In this study, 61% of QI preserve primary δ18O and 39% were associated with features that were linked to reset δ18O values. If δ18O in garnet is homogeneous and inclusions are removed, laser‐fluorination δ18O values of bulk garnet are more precise, more accurate, and best for thermometry. Intragrain δ18O(Grt) profiles measured in situ by ion microprobe show no δ18O zonation. Almandine–rich garnet (Alm60–75) from each sample was measured by laser‐fluorination mass‐spectrometry (LF‐MS) for δ18O and compared with ion microprobe measurements of δ18O in QI for thermometry. The Δ18O(Qz–Grt) values for Adirondack samples range from 2.66 to 3.24‰, corresponding to temperatures of 640–740 °C (A[Qz–Alm] = 2.71). Out of 12 samples that were used for thermometry, nine are consistent with previous estimates of peak temperature (625–800 °C) based on petrological and carbon–isotope thermometry for regional granulite and upper amphibolite facies metamorphism. The three samples that disagree with independent thermometry for peak metamorphism are from the anorthosite–mangerite–charnockite–granite suite in the central Adirondacks and yield temperatures of 640–665 °C, ~100 °C lower than previous estimates. These low temperatures could be interpreted as thermal conditions during late (post‐peak) crystallization of garnet on the retrograde path.

Aluminum and Gallium Substitution in Yttrium and Lutetium Aluminum–Gallium Garnets: Investigation by Single-Crystal NMR and TSL Methods

The work reports the results on 71Ga and 27Al NMR investigation of the gallium and aluminum ions distribution over tetrahedral and octahedral positions in the Y3Al5–x GaxO12:Ce single crystals and Lu3Al5–xGaxO12:Ce single-crystalline epitaxial films. The gallium content x varies between 0 and 5 in crystals and between 0.3 and 2 in films.. We find that in both the Y- and Lu-based solid solutions the larger gallium ions are preferably located at the tetrahedral position while the smaller aluminum ions prefer the octahedral position of the garnet host. Based on NMR data, the dependence of fractional occupation parameters of the tetrahedral site of Ga and Al ions on the Ga content is determined. In particular, in the Y3Al2Ga3O12:Ce crystal only 28% of Ga ions occupy octahedral sites, whereas 72% occupy tetrahedral ones. NMR investigations suggest that observed nonmonotonic dependences of electron trap depths monitored by thermally stimulated luminescence of Y3Al5–xGaxO12:Ce complex garnets on the Ga content a...

Assessment of mechanisms for enhanced performance of TiO2/YAG:Yb+3,Er+3 composite photocatalysts for organic degradation

Wastewater remediation is a key component to a sustainable water management program and the use of photo-activated catalysis has emerged as a promising advanced oxidative process for the decomposition of organic contaminants to innocuous products. Although the process is feasible using UV photons, only ∼5% of solar insolation is comprised of UV photons and few advances have been made to improve upon commercial TiO2 (i.e., P25). Here, composite catalysts containing both an upconversion phase (Yb+3/Er+3/Y-Al garnet or YAG host) and a photocatalyst (TiO2) are assessed for enhancing the photocatalytic activity of TiO2 for organic degradation using simulated insolation. Samples of the upconverting phosphor (YAG host) were prepared utilizing the Pechini method with varying molar concentration of Yb+3 ions [0%, 10%, 15%, or 20%] and a constant concentration of Er+3 ions [2%]. The composite materials were then obtained via calcination of the various YAG:Yb+3,Er+3 samples with titania at molar concentrations of [10%, 15%, or 20%]. Structures and properties of the upconverting phosphors and composite materials were verified with characterization analyses including X-ray diffraction, diffuse reflectance spectroscopy, transmission electron microscopy, and photoluminescence spectroscopy. For rose bengal degradation in a batch slurry reaction using a simulated ‘daylight’ spectrum as the irradiation source, results indicated that a mixed phased, Y-Al oxide doped with 2mol% Er+3 and 15mol% Yb+3 with 10mol% doped YAG/balance TiO2 composite yielded a 42% higher rate constant and apparent quantum yield than TiO2 alone. Additional kinetic studies with portions of the solar spectrum (i.e., UV bulbs or UV or IR LEDs) were conducted to further probe the effect of photon energies and suggested that rate and apparent quantum yield enhancements were largely attributed to increased amounts of organic adsorption and close proximity between phases, which coincided with the presence of the monoclinic phase (not cubic) of the Y-Al oxide structure. Upconversion and decreased charge carrier recombination rates were deemed to provide minimal contribution to these enhancements.

Quartz-in-garnet inclusion barometry under fire: Reducing uncertainty from model estimates

Abstract Quartz inclusions in garnet are suitable for barometry because quartz is highly compressible relative to garnet, and the garnet host can maintain large stress differences generated as pressure-temperature conditions change. However, experimental validation of the quartz-in-garnet approach has been limited, raising questions concerning the accuracy of calculated entrapment pressure. Here we test the results of quartz-in-garnet barometry by conducting in situ Raman analysis of natural inclusions over a range of temperatures (−175 to 600 °C). We assess the temperature (T) dependence of inclusion pressure (Pincl) at 1 bar and compare calculated entrapment pressures derived from measurements at different temperatures. Experiments used two quartz standards (oriented [c] and <a>) and fully encapsulated quartz inclusions from three different terranes, retaining different Pincl at room T (−444, 296, and 755 MPa). The stretched quartz inclusion (Pincl < 0) had the greatest increase in Pincl (+264 MPa, during heating from 25 to 500 °C), whereas the high-P inclusions underwent less change (+138 MPa) in Pincl over the same T interval. The greater T sensitivity of inclusions with low Pincl reflects the greater thermal expansivity of quartz near the α to β quartz transition. While measured Pincl-T trends are consistent with predictions, numerical models tend to overestimate Pincl at elevated T, and calculated entrapment pressures show an unrealistic dependence on reference T. Raman spectroscopic measurements conducted in situ at elevated T provide optimal results. In addition, we have recalibrated the thermal portion of the numerical method based on the present results, and provide new empirical expressions for improved quartz-in-garnet barometry.

Hydrous Na-garnet from Garnet Ridge; products of mantle metasomatism underneath the Colorado Plateau

This is the first report on amphibole exsolution in pyrope from the Colorado Plateau. Pyrope crystals delivered from mantle depths underneath the Colorado Plateau by kimberlitic volcanism at 30 Ma were collected at Garnet Ridge, northern Arizona. The garnet grains analyzed in this study occur as discrete crystals (without adjacent rock matrix) and are classified into two major groups, Cr-rich pyrope and Cr-poor pyrope. The Cr-poor pyrope group is divided into four subgroups based on exsolved phases: amphibole lamella type, ilmenite lamella type, dense lamellae type, and clinopyroxene/amphibole lamellae type. Exsolved amphibole occurs in amphibole lamella type, dense lamellae type, and clinopyroxene/amphibole lamellae type of Cr-poor pyrope. The amphibole crystals tend to have preferred orientations in their garnet hosts and occur as monomineralic hexagonal or rhombic prisms and tablets, and as multimineralic needles or blades with other exsolved phases. Exsolved amphibole has pargasitic compositions (Na2O up to 1.6 apfu based on 23 oxygen). Garnet host crystals that have undergone amphibole exsolution have low OH contents (2–42 ppmw H2O) compared to garnets that do not have amphibole lamellae (up to 115 ppmw H2O). The low OH contents of garnets hosting amphibole lamellae suggest loss of OH from garnet during amphibole exsolution. Amphibole exsolution from pyrope resulted from breakdown of a precursor “hydrous Na-garnet” composition (Mg,Na+ x)3(Al2 − x, Mgx)2Si3O12 − 2x(OH)2x. Exsolution of amphibole and other phases probably occurred during exhumation to depths shallower than 100 km prior to volcanic eruption. Based on the abundance and composition of exsolved clinopyroxene and amphibole lamellae in one garnet, hydrous Na-garnet had excess silicon (Si3.017 apfu, 12 oxygen normalization, vs. X3Y2Si3O12 for typical garnet). Comparison with experimental data suggests crystallization at pressures near 6–8 GPa. Garnet crystals that host exsolved amphibole have compositions (Pyp49-76, 3–10 wt% CaO, and up to 0.6 wt% Cr2O3) similar to garnets reported from pyroxenites, and have pyrope-almandine-grossular compositional ranges that overlap with the Cr-rich pyrope (typical lherzolitic garnet). Hydrous Na-garnet was likely formed by metasomatic reactions between Cr-rich pyrope and Na-rich aqueous fluid in the deep upper mantle. The most likely source of metasomatic Na-rich fluid is ancient oceanic crust that was subducted before subduction of the Farallon Plate beneath the Colorado Plateau.

Spectral Properties and Energy Transfer between Ce(3+) and Yb(3+) in the Ca3Sc2Si3O12 Host: Is It an Electron Transfer Mechanism?

The downshifting from Ce(3+) blue emission to Yb(3+) near-infrared emission has been studied in the garnet host Ca2.8-2xCe0.1YbxNa0.1+xSc2Si3O12 (x = 0-0.36). The downshifting does not involve quantum cutting, but one incident blue photon is transferred from Ce(3+) to Yb(3+) with an energy transfer efficiency up to 90% when x = 0.36 for the Yb(3+) dopant ion. For x ≤ 0.15, a multiphonon-assisted electric dipole-electric quadrupole mechanism of energy transfer dominates, while for the highest concentration of Yb(3+) employed, the electron transfer mechanism is confirmed. A temperature-dependent increase of the Ce(3+) → Yb(3+) energy transfer rate does not exclusively indicate the electron transfer mechanism. The application of the material to solar energy conversion is indicated.

Crystallographic orientation relationships in host–inclusion systems: New insights from large EBSD data sets

Crystallographic orientation relationships (CORs) between mineral inclusions and their hosts could potentially deliver information about inclusion formation processes and conditions. Most previous studies are based on small numbers of analyses. This paper uses EBSD to study host–inclusion CORs in an inclusion-rich Permian metapegmatite garnet (Koralpe region, Eastern Alps, Austria), demonstrating the importance of large data sets and of EBSD in particular for the analysis of CORs. The distribution of measured orientations reflects host garnet point group symmetry for 89% of inclusions analyzed (total N = 530). Each inclusion phase (rutile, corundum, and ilmenite) shows at least three different CORs to host garnet. “Statistical” CORs are introduced to describe distributions of inclusion orientations that have one or two degrees of freedom with respect to the host, but still reflect host crystal symmetry. Two end-member characteristics of statistical CORs are distinguished: rotation and dispersion. Most statistical CORs observed show a mixture of both. Each inclusion phase shows at least one statistical COR. Multiple coexisting CORs and statistical CORs are not restricted to rutile. Re-examination of previous garnet–rutile COR studies in light of the new results indicates that COR information may have been overlooked when using small data sets. Variation in COR parameters correlates with broad differences in assumed metamorphic conditions for new and literature samples, suggesting that petrogenetic information may be available if COR formation can be understood. The favorability of the detected CORs cannot be explained by a simple model involving minimization of misfit between lattice planes, implying that other interface properties or the inclusion formation mechanism are important controls on COR development.

Luminescent and scintillation properties of the Pr3+ doped single crystalline films of Lu3Al5−xGaxO12 garnet

The Pr3+ d–f luminescence was investigated in the single crystalline films (SCF) of Lu3Al5−xGaxO12:Pr garnet solid solution at x = 1–3, grown by the liquid phase epitaxy (LPE) method from the melt-solution based on the PbO–B2O3 flux. The shape of CL spectra and decay kinetics of Pr3+ ions in Lu3Al5−xGaxO12 SCFs strongly depend on the total gallium concentration x and distribution of Ga3+ ions between the tetrahedral and octahedral position of the garnet host. The best scintillation properties of Lu3Al5−xGaxO12:Pr SCF are achieved at the nominal Ga content in melt-solution in the x = 2–2.5 range.

Luminescence and energy transfer processes in (Lu,Tb)3Al5O12 single crystalline films doped with Ce3+

The luminescence properties of terbium lutetium aluminium garnet single crystalline films, Lu3−xTbxAl5O12, doped with Ce3+ are investigated as a function of the Tb/Lu ratio with aim of an improved understanding of the energy transfer processes between Ce3+ and Tb3+ ions in the aluminium garnet hosts. Due to replacing the smaller Lu3+ ion with the larger Tb3+ ion, the crystal field splitting for the 5d energy levels of Ce3+ ions increases, causing the shift of the lowest 5d state of Ce3+ below the 5D4 energy level of Tb3+. This allows for the efficient energy transfer from Tb3+ to Ce3+ even at the low temperatures. The measurements of temperature dependence of the decay time of Tb3+ and Ce3+ luminescence confirm an efficient energy transfer from Tb3+ to Ce3+ and provide a qualitative understanding of this process. Furthermore, bi-directional energy transfer processes between Ce3+ and Tb3+ are revealed. Scintillation decays under α-particles excitation show presence of the fast and slow sub-microsecond components.

Structural and luminescence effects of Ga co-doping on Ce-doped yttrium aluminate based phosphors

Herein, we primarily focus on luminescence spectrum measurements of various types of green emitting yttrium aluminate phosphors modified with gallium (Y3Al5-xGaxO12) synthesised by solid state reaction. The luminescent emission of samples depends on sample temperature and excitation radiation such as incident X-ray, electron and laser beam. Here, we measured radioluminescence (RL), cathodoluminescence (CL), photoluminescence (PL) along with XRD in order to clarify relationship between lattice defects and the spectral luminescence emissions. The RL and CL spectra of YAG:Ce exhibit an emission band ranging from 300 to 450 nm related to YAl antisite defects. The broad emission band of garnet phosphors is shifted from 526 nm to 498 nm with increasing of Ga3+ content, while full width at half maximum (FWHM) of the band tends to be greater than the width of unmodified YAG:Ce garnet. Deconvolution of the spectrum reveals that three emission bands centred at 139, 234 and 294 °C occur in aluminate host garnets.

New insights into the provenance of Saudi Arabian Palaeozoic sandstones from heavy mineral analysis and single-grain geochemistry

Saudi Arabian Palaeozoic siliciclastics cover a stratigraphic range from the Cambrian to the Permian. They crop out along the eastern margin of the Arabian Shield and are comprised of highly mature sandstones. Their heavy mineral assemblage reflects their mineralogical maturity and is dominated by the ultra-stable phases zircon, tourmaline and rutile. Less stable accessories are apatite, staurolite and garnet. Standard heavy mineral analysis of samples from two study areas in central/northern (Tabuk area) and southern (Wajid area) Saudi Arabia reveals distinct changes in provenance. Cambrian–Ordovician sandstones are first-cycle sediments, probably sourced from the ‘Pan-African’ basement. The overlying Hirnantian glaciogenic deposits consist of recycled Cambrian–Ordovician material. Devonian–Permian sandstones show a significant influx of fresh basement material, as attested by an increase of meta-stable heavy minerals. Single-grain geochemical analysis of rutile and garnet has proven to be a powerful supplementary technique. Rutile varietal studies reveal distinct differences in host rock lithologies between the two study areas: the Tabuk area contains predominantly felsic rutiles, whereas the Wajid area has more mafic input. Zr-in-rutile thermometry identified granulite-facies detritus in the lower Palaeozoic of the Tabuk area and has the potential to further define source areas. The distribution patterns of garnet host rock lithologies are remarkably similar in both study areas. They are dominated by amphibolite-facies metasediments and intermediate to felsic igneous rocks. Garnets derived from granulite-facies metasediments, which are scarce in the Arabian–Nubian Shield, also occur. Possible source rocks for high-grade garnets can be found in Yemen or farther south in the Mozambique Belt.

Excited state relaxation dynamics and up-conversion phenomena in Gd3(Al,Ga)5O12 single crystals co-doped with holmium and ytterbium

Single crystals of Gd3(Al,Ga)5O12 single doped with Ho3+ or Yb3+ ions and co-doped with Ho3+ and Yb3+ ions were grown by the Czochralski technique and investigated employing methods of optical spectroscopy. Rates of radiative transitions, branching ratio values and radiative lifetimes for excited multiplets of incorporated Ho3+ ions were determined based on the Judd–Ofelt treatment of optical absorption spectra recorded at room temperature. Absorption spectra and luminescence spectra recorded at 5 K made it possible to determine crystal field splitting for several low energy multiplets of Ho3+ ions and for the 2F5/2 multiplet of Yb3+ ions. Lifetimes of luminescent levels of incorporated holmium and ytterbium ions and the Yb3+ − Ho3+ energy transfer efficiency were determined based on analysis of recorded luminescence decay curves. Up-conversion of infrared radiation at 980 nm into yellow emission in crystals co-doped with holmium and ytterbium was observed and discussed. It was found that the structural disorder of the Gd3(Al,Ga)5O12 host resulting from a disparity of ionic radii of Al and Ga ions induces an inhomogeneous broadening of spectral lines of incorporated luminescent ions but the crystal field splitting of their multiplets is similar to that encountered in ordered garnet hosts. Based on analysis of gathered spectroscopic data it was concluded that the Gd3(Al,Ga)5O12:Ho3+,Yb3+ crystals are promising materials for the design of laser-diode pumped infrared lasers operating near 2000 nm.

Optical and scintillation properties of Ce3+-doped YGd2Al5−xGaxO12 (x=2,3,4) single crystal scintillators

The optical and scintillation properties of Ce3+-doped YGd2Al5−xGaxO12 (x=2,3,4) single crystals were investigated. With increasing Ga content in the garnet host, the 5d1 absorption and emission bands shift toward higher energy due to the decrease in the crystal field splitting of the 5d levels. Temperature dependences of absorption and emission spectra and of photoluminescence decays of both prompt and delayed components were measured. Light yield (LY) and its dependence on an amplifier shaping time were measured under excitation with γ-rays. High LY value of 38,000photons/MeV was obtained for a YGd2Al2Ga3O12:Ce sample. Scintillation decay was measured with an extended dynamical and temporal scale under the nanosecond-pulsed soft X-ray excitation. The relative content of the fastest component in the scintillation response increases with increasing Ga content.