Aluminum Garnet Research Articles

Energy transfer and radiative recombination processes in (Gd, Lu)3Ga3Al2O12:Pr3+ scintillators

(GdxLu3−x)Ga3Al2O12:0.3at.%Pr (x=0.025, 0.05, 0.1, 0.2, 0.4, 0.6) (GLGAG:Pr) polycrystalline powders are prepared by solid-state reaction method. To better understand the luminescence mechanism, the optical diffuse reflectance, photoluminescence emission and excitation, X-ray excited luminescence spectra and decay kinetics of GLGAG:Pr were investigated in detailed, allowing the determination of energy transfer from 5d state of Pr3+ to 4f state of Gd3+, and the non-radiative relaxation from 5d to 4f state of Pr3+. Besides, the former process plays more negative role in the emission quenching of GLGAG:Pr than later one. Pr3+ ion is regarded as an ineffective activation ion in Gd-based multicomponent aluminate garnets. In addition, the wavelength-resolved thermoluminescence spectra of GLGAG:Pr were studied after UV and X-ray irradiation. It is revealed that the localized recombination processes from electron traps to lower lying 4f levels of Pr3+ occurs without populating the higher 5d levels of Pr3+.

Functionalization of open-celled foams by homogeneous slurry based coatings

Abstract

Esthetic treatment of gingival hyperpigmentation with Nd:YAG laser or scalpel technique: a 6-month RCT of patient and professional assessment

This double-masked, randomized controlled trial with a split-mouth design aimed to compare patient- and professional-centered outcomes using different therapeutic approaches-neodymium-yttrium aluminum garnet (Nd:YAG) laser or scalpel technique-for gingival depigmentation. Patients presenting bilateral melanin gingival hyperpigmentation and who requested cosmetic therapy were recruited. Contralateral quadrants were randomly assigned to receive Nd:YAG laser (settings: 6W, 60mJ/pulse, and 100Hz) or scalpel technique. Patient morbidity experienced at intratherapy and during the first postoperative week was evaluated. In addition, after 6months, the cosmetic results achieved for the different therapeutic approaches were evaluated by patients and professionals. The chair time of each technique was also calculated. Patient-oriented outcomes concerning intratherapy morbidity did not demonstrate any differences between groups (p > 0.05), although a higher extent of discomfort/pain was experienced in the side treated by the scalpel technique compared to the Nd:YAG laser procedure during the first posttherapy week (p < 0.05). Regarding to cosmetic outcomes, no differences between techniques were observed for patient and professionals (p > 0.05). Significantly higher chair time was required for the scalpel technique than for the Nd:YAG laser therapy (p < 0.05). The Nd:YAG laser or the scalpel technique may be successfully used for the treatment of melanin gingival hyperpigmentation. However, the use of the Nd:YAG laser has presented advantages in terms of less discomfort/pain during the posttherapy period and a reduction of treatment chair time.

Greatly enhanced Dy3+ emission via efficient energy transfer in gadolinium aluminate garnet (Gd3Al5O12) stabilized with Lu3+

Dy3+-doped and Lu3+-stabilized gadolinium aluminate garnet solid solutions of [(Gd1−xLux)1−yDyy]3Al5O12 (x = 0.1–1.0, y = 0–0.10) have been developed as efficient phosphors for simultaneously strong blue (∼483 nm, the 4F9/2 → 6H15/2 transition of Dy3+) and yellow (∼584 nm, the 4F9/2 → 6H13/2 transition of Dy3+) emissions. The efficient energy transfer from Gd3+ to Dy3+ produces an additional excitation band, being the strongest, at ∼275 nm that corresponds to the 8S7/2 → 6IJ intra-f–f transition of Gd3+. With the energy transfer, significantly stronger Dy3+ emission (roughly two-fold) was obtained through excitation of Gd3+ at 275 nm rather than direct excitation of Dy3+ at 352 nm (6H15/2 → 4I11/2 + 4M15/2 + 6P7/2 transition, the strongest intra-f–f transition of Dy3+). The quenching concentration of Dy3+ was determined to be ∼2.5 at%, and the quenching mechanism was suggested to be dipole–dipole interactions. At the optimal Dy3+ content of 2.5 at%, increasing Lu3+ substitution tends to weaken both the excitation and emission bands owing to the higher electronegativity of Lu3+. Comparative studies showed that the best luminescent [(Gd0.8Lu0.2)0.975Dy0.025]AG phosphor has an integrated emission intensity roughly 2.5 and 4 times those of its (Y0.975Dy0.025)AG and (Lu0.975Dy0.025)AG counterparts, respectively. The effects of processing temperature and Lu3+/Dy3+ contents on phase evolution, crystal structure, particle morphology, PLE/PL properties, and fluorescence lifetime of the phosphor are thoroughly investigated. Owing to its enhanced emission and high theoretical density, the (Gd,Lu)AG:Dy3+ phosphor developed in this work may potentially be used as a new type of photoluminescent and scintillation material.

Ce3+-Tb3+ Energy Transfer in Aluminate Garnets

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Cervical Esophageal Hemangioma Combined with Thyroid Cancer

Hemangiomas that arise in cervical esophagus are extremely rare, representing 3.3% of all benign esophageal tumors. Although endoscopic mucosal resection (EMR) and potassium titanyl phosphate/yttrium aluminum garnet (KTP/YAG) laser therapy have been used with success for small tumors, the safety and efficacy in the case of large tumors remains uncertain. We report the successful resection of cervical esophageal hemangioma through a cervical esophagotomy in a patient with thyroid cancer who needed a cervical collar incision.

Investigating the influence of the operating frequency on the gas phase emitter effect of dysprosium in ceramic metal halide lamps

The dependence of the gas phase emitter effect of Dy on a variation of the operating frequency between a few Hz and 2 kHz is investigated in a high intensity discharge lamp. The buffer gas of the lamp consisting of Ar, Kr and predominantly Hg is seeded with DyI3, its burner vessel is formed from transparent yttrium–alumina–garnet material. Phase and spatial resolved emission spectroscopy in front of the lamp electrode and pyrometric temperature measurements along the tungsten electrode are performed with a spectroscopic setup. Dy atom and ion densities in front of the electrode are deduced from absolute intensities of optically thin Dy lines and a plasma temperature, derived from the absolute intensity of mercury lines. Phase resolved values of the electrode tip temperature Ttip and input power Pin are obtained from temperature distributions along the electrode. Distinctly higher Dy ion and atom densities are measured in front of the electrode within the cathodic phase. With increasing operating frequency a reduction in both atoms and ions is observed in front of the cathode. In contrast, an increase in the ion density in front of the anode is seen. Moreover, the Dy ion density is drastically reduced by an additional seeding of the lamp with TlI. It is found that an up rating of the Dy ion density is correlated with a decline of Ttip and Pin. At higher frequencies this effect takes place not only within the cathodic phase but also within the anodic phase. The reduction of the average electrode tip temperature of the order of several hundred kelvin compared with a YAG lamp with a pure mercury filling is explained by a Dy monolayer on the electrode surface which is sustained by a Dy ion current.

Synthesis of an aluminum nitride–yttria (AlN–Y2O3) composite from nano-sized porous AlN and YCl3

In order to enhance the thermal conductivity of aluminum nitride (AlN) with sintering additives including yttria (Y2O3), it is necessary to form yttrium aluminate garnet (YAG) and secondary phases both within and around the boundaries of AIN drains. Nano-sized porous AlN particles were produced to form YAG and secondary phases within AlN grains, after which a AlN–Y2O3 nano–nano composite was formed from AlN and amorphous Y2O3. Porous AlN powders were first successfully synthesized by the chemical vapor synthesis (CVS) method. Highly crystalline and nano-sized porous AlN powders were synthesized at 1,200 °C. Brunauer–Emmett–Teller (BET) analysis showed that these powders had very large surface areas, suggesting that the particles approached nano-scale sizes with very small pores. To form composites of Y2O3 and AlN, we prepared a yttrium source solution that infiltrated the nano-sized pores of the AlN particles. Such an infiltration of AlN with amorphous Y2O3 was expected to effectively reduce the residual oxygen content by facilitating the formation of YAG and secondary phases during the sintering process. We characterized the composite powders of AlN–Y2O3 and the sintered bodies using BET, XRD, SEM, TEM, and thermal conductivity analyses.

Amorphization of rare earth aluminate garnets under ion irradiation and decay of 244Cm admixture

The stability of synthetic REE-aluminate garnets irradiated by accelerated Kr2+ ions and affected by alpha decay of 244Cm (T1/2 = 18.1 yr) has been studied. The dose of irradiation sufficient for the complete disordering of the aluminate garnet structure is 0.40–0.55 displacements per atom. This value increases with rising temperature due to the increasing intensity of recovery from radiation damage to the lattice by heating. The critical temperature above which the structure of REE-aluminate is not damaged by radiation is 550°C. The amorphization dose for aluminates with garnet structure is two to three times higher than of that previously studied ferrites; the critical temperature of both is similar. In resistance to radiation, aluminate garnets do not yield to zirconolite and exceed titanate pyrochlore. Heating to 250°C does not lead to substantial recovery from radiation defects in the garnet structure. The radiation impact on matrices of real actinide (An) wastes is lower than that related to ion irradiation and 244Cm doping, and this facilitates a higher radiation resistance of garnets containing HLW.

Remnants of oceanic lower crust in the subcontinental lithospheric mantle: Trace element and Sr–Nd–O isotope evidence from aluminous garnet pyroxenite xenoliths from Jiaohe, Northeast China

Pyroxenite xenoliths entrained in alkali basalts are usually interpreted to be high pressure cumulates from mantle-derived melts. However, those from Jiaohe, Northeast China may have originated from subducted oceanic crust. Their high bulk Al 2O 3 contents (12.2–17.4%) and Mg# (up to 0.88) resemble those of olivine-bearing cumulative gabbros. A crustal origin for the Jiaohe pyroxenites from plagioclase-bearing protoliths is further supported by positive Eu and Sr anomalies in both whole rock and in garnet and clinopyroxene analyses, low HREE abundances in garnet and low δ 18O (4.9–5.1‰) relative to typical mantle values (5.5‰). Compared with average values for the corresponding mantle minerals, the δ 18O values of the Jiaohe clinopyroxene (4.5–5.4‰) are lower, the δ 18O values of garnet (5.1–5.6‰) are similar, whereas those of spinel are higher (5.2‰). In particular, there are disequilibrium O isotopic fractionations between garnet/spinel and clinopyroxene, resembling those of plagioclase/clinopyroxene pairs in seawater-altered oceanic crust. This is attributed to spinel and garnet inheriting their O isotope characteristics from plagioclase prior to transformation to these minerals during subduction metamorphism of altered oceanic gabbros, without isotopic re-equilibration at mantle conditions. Identification of remnants of subducted oceanic crust in the subcontinental lithospheric mantle is important to understanding mantle heterogeneity and genesis of intraplate magmatism.

Influence of blue-light polarization on light scattering in nanocrystal luminescent glass for white light-emitting-diodes

The influence of the polarized state of blue light on light scattering in InGaN blue chip nano-crystal luminescent glass for solid state lighting is investigated. Based on Rayleigh-Debye approximation theory, theoretical relationships between the light scattering turbidity and wavelength of the incident light, radius and refractive index of the nano-crystals are established to simulate the situations in yttrium aluminate garnet (YAG), silicate and oxynitride based luminescence glass. It is revealed that the scattering turbidity in luminescent glass turns to be the smallest as the effective refractive index of nanocrystals is equal to that of parent glass, and the scattering turbidity for the vertically polarized incident light is greater than that for the un-polarized incident light, while that for the horizontally polarized incident light is smaller than that for the unpolarized incident light under the same conditions.

Phonon recycling in ion-doped lasers

Phonon emission is an energy-conversion efficiency loss in photonic transition processes. Phonon recycling by the anti-Stokes cooling results in a lower operating temperature. Transmitted optical phonons cross heterogeneous boundary and the upconverted acoustic phonons contribute to higher occupancy of the optical phonon and increase the second-order transition rate. Optimization of phonon spectra makes upconversion favorable. We present theoretical study and quantitative efficiency results for phonon recycling in Yb3+ doped yttria alumina garnet lasing layer and its adjacent Yb3+:ZrF2 cooling layers and examine the thermodynamic limits. It is predicted that 30% of emitted phonons are recycled and further improvement is possible.

Quenching of Orange-Red Ce3+ Emission in Garnet Phosphors

Ce3+-doped aluminate garnets are the main phosphors used in solid-state lighting based on blue light emitting diodes (LEDs). Recently, different compositional modifications of garnet hosts have been shown to significantly redshift the yellow-green Ce3+ emission in the garnets. We investigate the high temperature quenching of these phosphors to determine any limitations towards red emission in Ce3+-doped garnets.

Formation of ultrafine eutectic-like microstructures of various rare earth oxide-Al2O3 systems by use of amorphous phases

Ultrafine eutectic-like microstructures of various rare earth (RE) oxide-Al2O3 systems were formed by use of amorphous phases. This new method uses a low migration rate in the amorphous phases. Mixtures of RE oxide (RE: Yb, Dy, Er, Ho, Gd, Sm, Eu) and Al2O3 powders with the eutectic compositions were melted and quenched rapidly to form the amorphous phases. A heat treatment of the amorphous phases of various eutectic systems at 1000 and 1300 °C, for 30 min, formed RE aluminum garnet (RE3Al5O12)/Al2O3 phases or RE aluminum perovskite (REAlO3)/Al2O3 phases. Scanning electron microscopy observation of these materials heat-treated at 1300 °C showed eutectic-like microstructures, in which crystals of eutectic component were entangled with each other. Furthermore, the microstructures were much finer than those of materials generally prepared from eutectic melts. In this study, it was confirmed that this method is useful for the formation of ultrafine eutectic-like microstructures for many eutectic systems.

Transparent ceramics for lighting

The development of ceramic arc lamps for optical applications requires consideration of materials other than sintered polycrystalline alumina (PCA). Regular PCA is translucent, not transparent. Except small-grained, regular PCA cannot be used for high luminance applications such as required by projection systems. Silica lamps are currently operating close to their limit in highly loaded discharge lamps. These may be replaced with ceramic lamps so the Hg pressure may be elevated and/or higher powers achieved. Cubic materials can be polished to transparency for use as optical sources of short arcs. The current paper surveys the composition, structure, and properties of transparent ceramic lamp tube materials including small-grained PCA, sapphire, aluminum oxynitride, yttrium aluminate garnet, and dysprosium oxide. The challenges beyond the optical transparency are to achieve (1) strong bonding between the transparent ceramic and electrode system to complete the discharge enclosure, (2) satisfactory characteristics including thermo-mechanical properties in order to withstand the rapid heating and cooling cycles encountered in both the discharge tube and seal, (3) durability to resist the attack from lamp chemicals at high temperatures, and (4) stability to maintain the optical quality throughout the life. Performance, energy efficiency, environmental sustainability, and economics are driving the development of ceramic envelopes in lighting products. Transparent ceramics offer opportunities to push the limits of envelope materials for improved lamps. The paradigm used during the course of transparent ceramics research exemplifies advancement of new and improved materials.

The acoustical research of shear viscoelastic properties of nanoparticles suspensions

The acoustical research of some physical properties of nanoparticles suspensions has been carried out in this work. Mechanical properties of the SiO2 and YAG particles suspensions have been investigated. Resonance method is used for measurement of viscoelastic properties (shear modulus and shear viscosity) of the suspensions. It was shown that the viscosity and elasticity depend on size and concentration of particles. Colloid suspension of nanoparticles of silica dioxide (SiO2) and yttrium alumina garnet doped by neodymium (Nd:YAG ) are synthesized. The shear viscoelastic properties of the colloid suspensions have been measured by acoustical method. The researching of colloid suspension of SiO2 nanoparticles of different concentration by the acoustical resonance method is shown that viscosity and shear modulus decrease with nanoparticle concentration increasing. The nonlinear behavior of viscosity and elasticity in depending on shear influence amplitude has been shown. Investigation of viscosity of suspensions of Nd:YAG nanoparticles in ethanol in depending on concentration has been carried out. The decreasing of shear modulus of the suspensions with concentration decrease has been shown. The work was supported by RFBR 05-02-16584a and 07-02-90103-Mong-a.

Evolução metamórfica/metassomática paleoproterozóica do Complexo Saúde, da Bacia Jacobina e de leucogranitos peraluminosos na parte norte do Cráton do São Francisco

The Saude Complex and the Jacobina Basin, located in the northern part of the Sao Francisco Craton, are constituted by metasedimentary rocks, metamorphosed during the paleoproterozoic orogeny (≈ 2.08-1.88 Ga), and are associated to leucogranites. The kinzigites and the non-garnetiferous paragneisses of the Saude Complex, the aluminous schists of the Jacobina Basin and the leucogranites contain mineral assemblages related to the orogenic collision. The garnet in the kinzigites and staurolite in the paragneisses, associated to sillimanite + quartz + biotite, constitute mineral assemblages formed during the progressive metamorphic path whereas cordierite and plagioclase crystallized during the retrometamorphism associated to the orogenic decompression. In the aluminous schists, garnet and staurolite crystallized during the metamorphic progressive path, but andaluzite and plagioclase record the retrometamorphism. The non-garnetiferous paragneisses, the andaluzite-schists and the leucogranites have fibrolite-quartz-muscovitebearing microstructures formed from the circulation of reducing fluids that lixiviated mainly base-cations of the preexisting silicates. Those microstructures characterize an event of metasomatism that occurred during and/or after the orogenic decompression with the leucogranites acting as thermodynamic triggers in the mobilization of the crustal fluids. The metasomatic event was responsible for almost isobaric inflections (≈ 3.0 kbar) in the regressive P–T path of the non-garnetiferous paragneisses and of the aluminous schists, toward temperatures near 600oC. The absence of fibrolite and muscovite in the kinzigites besides geothermometry estimations, placed between the low-granulite and the high-amphibolite facies, suggest allochthonous positioning of those rocks originated from the orogen infracrust.

Evolução metamórfica/metassomática paleoproterozóica do Complexo Saúde, da Bacia Jacobina e de leucogranitos peraluminosos na parte norte do Cráton do São Francisco

The Saúde Complex and the Jacobina Basin, located in the northern part of the São Francisco Craton, are constituted by metasedimentary rocks, metamorphosed during the paleoproterozoic orogeny (≈ 2.08-1.88 Ga), and are associated to leucogranites. The kinzigites and the non-garnetiferous paragneisses of the Saúde Complex, the aluminous schists of the Jacobina Basin and the leucogranites contain mineral assemblages related to the orogenic collision. The garnet in the kinzigites and staurolite in the paragneisses, associated to sillimanite + quartz + biotite, constitute mineral assemblages formed during the progressive metamorphic path whereas cordierite and plagioclase crystallized during the retrometamorphism associated to the orogenic decompression. In the aluminous schists, garnet and staurolite crystallized during the metamorphic progressive path, but andaluzite and plagioclase record the retrometamorphism. The non-garnetiferous paragneisses, the andaluzite-schists and the leucogranites have fibrolite-quartz-muscovitebearing microstructures formed from the circulation of reducing fluids that lixiviated mainly base-cations of the preexisting silicates. Those microstructures characterize an event of metasomatism that occurred during and/or after the orogenic decompression with the leucogranites acting as thermodynamic triggers in the mobilization of the crustal fluids. The metasomatic event was responsible for almost isobaric inflections (≈ 3.0 kbar) in the regressive P–T path of the non-garnetiferous paragneisses and of the aluminous schists, toward temperatures near 600oC. The absence of fibrolite and muscovite in the kinzigites besides geothermometry estimations, placed between the low-granulite and the high-amphibolite facies, suggest allochthonous positioning of those rocks originated from the orogen infracrust.

Color centers induced in Y3Al5O12 single crystals by swift heavy ions and reactor neutrons

The induced damage in single crystals of yttrium alumina garnet (Y3Al5O12) bombarded at GANIL with 561MeV 51Cr, 466MeV 128Te, and 957MeV 208 Pb ions, and at Algiers with reactor neutrons has been studied by optical measurements. Optical absorption bands centered at 250, 300 and 380nm are observed after irradiation with ions and neutrons. The variation of the absorption as a function of fluence and electronic stopping power are presented and discussed. Photoluminescence, excited from 380nm optical absorption band of this garnet is measured at room temperature. The results show the increase of the emission band width with increasing electronic stopping power. The confrontation of the results obtained with ions and neutrons irradiation confirm the contribution of the energetic heavy ions to point defects production. Furthermore, the existence of an electronic stopping power threshold between 10 and 15keV/nm for oxygen ions displacements is derived.

Rare earth element diffusion in natural enstatite

Chemical diffusion coefficients of La, Nd, Eu, Gd, and Yb in natural enstatite have been measured at 850–1250 °C and 1 atm. Anhydrous diffusion experiments were run in Pt capsules in air, or in sealed silica glass capsules under an iron–wüstite (IW) solid buffer. The sources of diffusant were pre-reacted mixtures of synthetic enstatite powder and microcrystalline rare-earth aluminate garnet. Rutherford Backscattering Spectrometry (RBS) was used to measure diffusion profiles. For Gd diffusion in air over the temperature range 1000–1250 °C, the following Arrhenius relation is found for diffusion normal to (210): D Gd,air = 2.55 × 10 - 9 exp ( 321 ± 85 kJ mol - 1 / RT ) m 2 s - 1 . There is no significant difference between Gd diffusion in air and under IW-buffered conditions. Behavior similar to Gd is also noted for Nd. The Arrhenius relationship for Eu diffusion in enstatite, normal to (210) and at 850–1150 °C and IW-buffered conditions, is D Eu,IW = 6.93 × 10 - 6 exp ( - 384 ± 29 kJ mol - 1 / RT ) m 2 s - 1 . For Eu diffusion in air over the temperature range 1000–1200 °C for the same orientation, the following Arrhenius relation is found: D Eu,air = 1.70 × 10 - 8 exp ( - 350 ± 42 kJ mol - 1 / RT ) m 2 s - 1 . For Eu diffusion under IW-buffered conditions and for experiments run in air, diffusivities normal to (001) are similar to those for diffusion normal to (210). Eu diffusion under IW-buffered conditions is more than an order of magnitude faster than Eu diffusion in air. It is likely that majority of Eu is in the divalent state for diffusion under IW-buffered conditions, but Eu is in the trivalent state for diffusion in air. In the case of Nd and Gd, where valence state does not change under the investigated fO 2 conditions, diffusivities measured for experiments run both in air and under IW-buffered conditions are comparable to those obtained for trivalent Eu. Further, measurements of La, Nd, Eu +3, Gd, and Yb diffusion suggest that diffusion of trivalent REE in enstatite is not sensitive to ionic size, in contrast to that observed for REE diffusion in diopside [Van Orman, J.A., Grove, T.L., Shimizu, N., 2001. Rare earth element diffusion in diopside; influence of temperature, pressure, and ionic radius, and an elastic model for diffusion in silicates. Contrib. Mineral. Petrol. 141, 687–703]. These differences in diffusive behavior of REE between diopside and enstatite, as well as Eu 2+ and Eu 3+ in enstatite, can result in significant REE fractionation between coexisting pyroxenes during partial melting, melt migration, and subsolidus reequilibration processes in the Earth’s mantle and that of the Moon.