Yttrium Aluminum Garnet Ceramics Research Articles

Effect of yttrium variation on phase, transparency, and micro-structure of neodymium doped yttrium aluminum garnet ceramic

Neodymium doped transparent yttrium aluminum garnet ceramics with yttrium excess and deficient (1 to 3 mol%) compositions were fabricated. The samples with stoichiometric and 1.0 mol% yttrium excess are transparent. However, 1.0 mol% yttrium deficiency samples are opaque. The structural and compositional analysis corroborates the presence of alumina as secondary phase for yttrium deficient compositions and yttrium aluminum perovskite for yttrium excess compositions. It is found that yttrium deficiency is highly detrimental to the transparency as compared to yttrium excess. The solubility width of garnet phase is found to be lower than 1.0 mol% for yttrium excess and deficiency.

Ce: <i>YAG </i>ceramics: effect of synthesis technology on luminescent and optical properties

The paper studies the influence of the synthesis technology on the luminescent and optical characteristics of transparent Ce doped yttrium aluminum garnet ( YAG ) ceramics synthesized in two ways. The transparency of samples with a size of Ø10×2 mm reaches 60 to 81 % in the 500-900 nm wavelength range. The effect of intermediate synthesis steps on the optical characteristics and final concentration of the Ce3+ activator in the YAG ceramic has been described and discussed

Temperature-dependent fluorescence decay and energy transfer in Nd/Cr:YAG ceramics

This work investigates the energy-transfer processes from Cr3+ to Nd3+ in yttrium aluminum garnet (YAG) ceramics by comparing the fluorescence decay of Cr3+ for Nd/Cr:YAG with that of Cr:YAG from 293 to 473 K. The experimentally determined fluorescence decay of Nd3+ excited through Cr3+ is consistent with the theoretical predictions when energy-transfer processes are taken into account by including in the rate equations the dipole-dipole interaction and energy transfer via excitation-energy migration. Furthermore, the results presented herein clarify that the efficiency of energy transfer from Cr3+ to Nd3+ increases slightly with increasing temperature.

Luminescent Yttrium–Aluminum Garnet Ceramics Obtained by Conventional Sintering on Air

Abstract—An yttrium aluminum garnet (YAG) luminescent ceramic activated by Ce3+ has been obtained by uniaxial static pressing followed by sintering in air at a temperature of 1650°C. The initial phosphor powder was characterized and the linear shrinkage dynamics studied. The morphological, elastoplastic, and optical-luminescent properties of the obtained YAG:Ce ceramic samples were studied. The technological mode for manufacturing ceramics of this type with a density of at least 98% and luminescence efficiency of 45% was determined.

Luminescence behaviour of a Yb sensitized Er:YAG transparent ceramic prepared by the solid-state reaction method

Optical-grade yttrium aluminum garnet (YAG) ceramics co-doped with Yb3+ and Er3+ ions are successfully prepared via using high-temperature solid-state reaction method under vacuum condition. Cubic phase structure and full dense microstructure are determined by means of X-ray diffraction (XRD) and scanning electron microscope (SEM) methods. Both characteristics endow our ceramic with high optical transmittance of ~82% at 600 nm. Moreover, the ceramic luminescent properties are mainly discussed with Yb3+ ions serving as an efficient sensitizer for Er3+ active centers. Both zero-phonon lines (ZPLs) and sidebands of Er3+ ions in the YAG ceramics are first analyzed and the most interesting finding of this work is the anti-Stokes sidebands showing remarkably stronger emission intensity than Stokes ones. This obtained result reveals the predominance of absorbing phonon energy in vibronic luminescence process under the weak crystal field.

Laser sintering and photoluminescence study of Tb-doped yttrium aluminum garnet ceramics

This work focuses on the fabrication and luminescent characterization of Tb-doped yttrium aluminum garnet (Y3Al5O12:Tb; YAG:Tb) ceramics produced using the laser sintering technique. In this technique, a CO2 laser is employed as the main heating source to promoting the sintering. YAG powders with different Tb concentrations were prepared by the polymeric precursor method and presented single cubic crystalline phase after calcination at 1000 °C in air for 2 h. Ceramic bodies were fabricated by laser sintering of uniaxially pressed pellets using a CO2 laser at a power level of 3.3 ± 0.1 W/mm2 for 90 s. To sintering, the green sample were put inside a sample holder, that improved the density, microstructure and avoided ablation effect. The resultant ceramics exhibited a high relative density of about 98–99 ± 1%, good microstructural homogeneity as verified by scanning electron microscopy, and a single cubic crystalline phase as determined by X-ray diffraction. X-ray absorption near edge structure measurements taken at the Tb LIII edge showed Tb to be exclusively in the trivalent state.

Determining E1 and E2 values for yttrium aluminum garnet ceramics using the Duane-Hunt limit.

A major challenge when performing scanning electron microscopy and X-ray analysis on many ceramic materials is their electrical insulation properties, which leads to buildup of the surface charge and reduced contrast in the secondary electron image. A new procedure was established to quantitatively determine the neutral state values, E1 and E2 , of yttrium aluminum garnet (YAG) ceramics using the Duane-Hunt limit (EDHL ) of Bremsstrahlung, in order to eliminate this charge effect. Thirty-eight EDHL values were linearly fitted with the last portion of X-ray spectra acquired under the incident energy, E0 , from 0.35 to 5.0 kV. According to the distribution of EDHL , two piecewise linear fitting was first employed with a breakpoint of 1.0 kV. Consequently, two intersection points of 0.54 and 2.48 kV, which correspond to E1 and E2 for YAG ceramics, were directly determined using a theoretical curve (EDHL = E0 ). As a result, the high-resolution images of the YAG ceramic grain structure were successfully obtained using the calculated E1 and E2 values.

Comparison of synthesis and spark plasma sintering of YAG nano particles by variation of pH and precipitator agent

Yttrium aluminum garnet ceramics with a wide range of technological and industrial applications have attracted great attention owing to their remarkable mechanical, thermal and optical features. The properties of transparent or translucent YAG ceramics with wide-ranging applications notably depend on the features of the starting particles which is directly affected by synthesis conditions. In this study, yttrium aluminum garnet precursors (YAG) were obtained by reverse co-precipitation method from a mix solution of aluminum and yttrium nitrates using ammonium hydrogen carbonate (AHC) and ammonia water (AW) solutions as precipitator agents. The effect of pH on the chemical composition and phase analysis of the precursors synthesized by different precipitants was explored, leading to the formation of precursors with the proper stoichiometric ratio of YAG phase. The phase evaluation process, thermal behavior, microstructures and other characteristics were compared for the two precipitants by ICP, XRD, FTIR, TG-DTA, BET, FESEM, TEM and EDX analysis. The results revealed that unlike AW, using AHC as precipitant at high pH values caused deviation from the YAG stoichiometric ratio. In the pH value of 7, both precipitants produced homogenous precipitates and pure YAG at a calcination temperature of 900 °C while the powders obtained by AHC exhibited more dispersity and fewer aggregates.Sub-micron-grained YAG ceramics were obtained by SPS method at 1380 °C for 10 min using amorphous nano particles without adding any sintering aids. Compared with ceramics produced using synthesized powders by AW, the ceramic of co-precipitated powders by AHC showed higher density (99.9%) and transparency (33% at 680 nm and 50% at 1100 nm).

Heat treatment of transparent Yb:YAG and YAG ceramics and its influence on laser performance

Composite transparent ceramic materials are promising for improving the performance of high–average-power lasers. A combination of room-temperature bonding via surface treatment by a fast atom beam and diffusion bonding via heating, which effectively controls the ion diffusion distance near the interface, makes the laser materials suitable for a variety of oscillator/amplifier. During the heat treatment of yttrium aluminum garnet (YAG) ceramics, the Si ions in the solid solution of the sintering aid incorporated within the grains were seen to segregate at the grain boundary, resulting in an increase of scattering sites. The number density and size of the scattering sites strongly depended on the post-heating temperature rather than the heating time. Specifically, heating at 1300 °C did not affect the transmittance of the YAG ceramic, whereas both the size and number of scattering sites substantially increased with a heat treatment at 1400 °C. The laser oscillation experiment using cryogenically-cooled Yb:YAG ceramics exhibited heating temperature dependence of the slope efficiency owing to the increasing scattering loss.

Nanometer-scale characteristics of polycrystalline YAG ceramic polishing

Polycrystalline yttrium aluminum garnet (YAG) ceramics used as laser gain media require nanometer-scale surface geometries to minimize light scattering. Generally, uneven material removal between grains and excessive material removal at the grain boundaries retards smoothing of the ceramic surfaces. This paper describes the effects of the mechanical properties and polishing tool structures on the tool contact against the target surface during polishing. This, in addition to the abrasive type and size, influences the polishing characteristics, especially the material removal at the grain boundaries, the grain enhancement, the grain dislodgement, and the resulting nanometer-scale geometries of the polished surfaces.

Preparation of YAG nanopowder by different routes and evaluation of their characteristics including transparency after sintering

Yttrium aluminium garnet (YAG) nanopowder has been synthesized by five different routes: three of them are co-precipitation with different combinations of aluminium and yttrium sources as well as the precipitating agents, and the rest are by solid state synthesis with certain variation. They are designated as: process-1 (Al-nitrate, yttria, HNO3, NH4HCO3), process-2 (Al-nitrate, Y-nitrate, NH4HCO3), process-3 (Al-nitrate, Y-nitrate, NH4OH,), process-4 (Al-nitrate and Y-nitrate heated to 1000 °C), and process-5 (alpha-alumina and yttria heated to 1100 °C). Of them, process-2 develops the highest surface area (31 m2/g), soft agglomerated and near spherical crystalline YAG nanopowders through minimum mass loss, and excellent cation homogeneity. Pseudo solid state reaction between aluminium nitrate/yttrium nitrate (process-4) and solid state reaction of alumina/yttria (process-5) requires high-calcination temperature and results in hard agglomerates. In most cases, highly crystalline YAG is formed together with the formation of an intermediate metastable phase of YAP. Powder prepared by process-2 leads to 99.6% dense and 60% transparent YAG ceramics on hot isostatic pressing.

Ultrafast postprocessing of yttrium aluminum garnet ceramics via femtosecond pulse laser irradiation

We studied rapid densification and homogenization of sintered yttrium aluminum garnet (YAG) ceramics via sintering followed by femtosecond pulse laser (800 nm) irradiation. We formed localized, high-density microstructures within a YAG ceramic matrix. The laser irradiated regions were characterized using scanning electron microscopy, elemental mapping, and x-ray diffraction. Our results show that phase separation of YAG into YAlO3 and Al2O3 can be obtained in situ within stoichiometric YAG. With an optimum laser power and processing conditions, this process can be used for producing dense YAG ceramics.

Quantification of non-stoichiometry in YAG ceramics using laser-induced breakdown spectroscopy

Strict control of composition is of paramount importance for the reproducible fabrication of advanced ceramics. In particular, the preparation of high-grade transparent ceramics of definite line-compounds requires that the ratio of major constitutive elements be quantified with a precision better than a fraction of a mole percent to prevent the precipitation of secondary phases and the scattering of light. Such a requirement poses difficult challenges to most analytical methods, especially when applied to nearly-stoichiometric insulating phases. In this work, we show that laser-induced breakdown spectroscopy (LIBS) is a well-suited technique for the assessment of non-stoichiometry in yttrium aluminum garnet (YAG) ceramics and that the aluminum to yttrium ratio can be determined with a resolution of 0.3 mol %, well within the phase boundaries of YAG.

Synthesis and characterization of Ce:YAG nano-phosphors and ceramics

Yttrium aluminum garnet (YAG), Y3Al5O12 is one of the most important optical materials with many applications such as optical windows, laser host materials, detectors and phosphors. Nano YAG could offer many advantageous over bulk materials and large grain size phosphors. In this work Ce doped YAG (Ce:YAG) nanophosphors (NP) were synthesized using simple chemical methods and crystalized by annealing at 800, 900 and 1100°C. Luminescence was recorded in the range of 200 to 800 nm using X-ray induced luminescence technique to detect all emission centers in the sample and evaluate their relative intensities. The effect of annealing temperature and the use of different complexing and polymerization agents on the particle morphology and luminescence were investigated. Trapping phenomena were studied in Ce:YAG NP and bulk ceramics by thermally stimulated luminescence spectroscopy and a comparison was made between them and Ce:YAG single crystals. Measurements concluded that trapping is dominated by crystal defects in single crystals and by trapping sites at the grain boundaries in ceramics. Ce:YAG NPs -on the other hand- are free of traps, which seems to be characteristic of their small grain structure. This study illustrates the effect of chemical agents and annealing temperatures on the structural and optical properties of Ce:YAG nanophosphors and shed light on the nature and characteristics of traps in YAG, which greatly affect its performance in a wide range of applications. Furthermore it reveals that different trapping mechanisms take place among single crystals, bulk ceramics and NPs which could have impact on understanding the optical and scintillation properties of various luminescent materials.

Polishing Characteristics of Transparent Polycrystalline Yttrium Aluminum Garnet Ceramics Using Magnetic Field-Assisted Finishing

Transparent polycrystalline yttrium aluminum garnet (YAG) ceramics have garnered an increased level of interest for high-power laser applications due to their ability to be manufactured in large sizes and to be doped in relatively substantial concentrations. However, surface characteristics have a direct effect on the lasing ability of these materials, and a lack of a fundamental understanding of the polishing mechanisms of these ceramics remains a challenge to their utilization. The aim of this paper is to study the polishing characteristics of YAG ceramics using magnetic field-assisted finishing (MAF). MAF is a useful process for studying the polishing characteristics of a material due to the extensive variability of, and fine control over, the polishing parameters. An experimental setup was developed for YAG ceramic workpieces, and using this equipment with diamond abrasives, the surfaces were polished to subnanometer scales. When polishing these subnanometer surfaces with 0–0.1 μm mean diameter diamond abrasive, the severity of the initial surface defects governed whether improvements to the surface would occur at these locations. Polishing subnanometer surfaces with colloidal silica abrasive caused a worsening of defects, resulting in increasing roughness. Colloidal silica causes uneven material removal between grains and an increase in material removal at grain boundaries causing the grain structure of the YAG ceramic workpiece to become pronounced. This effect also occurred with either abrasive when polishing with iron particles, used in MAF to press abrasives against a workpiece surface, that are smaller than the grain size of the YAG ceramic.

Effect of Sintering Aids on the Properties of Porous YAG Ceramics

Yttrium aluminum garnet (YAG) with a chemical composition of Y3Al5O12 is an important advanced structural and functional material due to some excellent properties. The porous YAG ceramics were prepared via vacuum sintering technology, the effect of sintering aids on the properties of porous YAG ceramics were investigated in this paper. Through an analysis and discussion, the conclusions are that the porosity increases with the increasing sintering temperature from 1300°C to 1500°C, the pore is moved to the surface of sample, which forms the open pore to make the porosity increase, the more and bigger sintering neck is increased. Porous YAG ceramics are sintered at 1500°C, the regular outside shapes of porous YAG ceramic are kept using CaO and MgO as sintering aids, the outside shape of porous YAG ceramic is wrecked using Al2O3 as sintering aids, which shows the over fired phenomenon.

Luminescence of Yb-doped YAG: Divalent ytterbium ions

This study reports the presence of Yb2+ ions with 4f136s electron configuration of the ground state in addition to Yb3+ ions in yttrium aluminium garnet ceramics activated by ytterbium. Pulsed cathodoluminescence and transmission spectra of divalent ytterbium ions appear as narrow lines of s↔s transitions at 913–1050nm range. These ions in association with oxygen vacancies generate Re–F centres which are able to absorb at 280, 365, 630nm and emit at 325, 520, 590−720nm in d↔s transitions of Yb2+ ions; the emission band at 590–720nm consists of eight narrow lines. The Re–F centeres are manifested most clearly in the ceramic samples obtained directly after vacuum sintering at 1800°C.

Radioluminescence emission of YAG:RE laser-sintered ceramics

A laser sintering technique was used to consistently and quickly sintering yttrium aluminum garnet (YAG) ceramics doped with Ce3+, Tb3+, or Eu3+. The ceramic powders were synthesized by the polymeric precursor method presenting single crystalline phase after calcination at 1000°C for 6h. The ceramics were sintered by a laser sintering technique in which a CO2 laser is used as the main heating source. The laser-sintered ceramics presented high relative density (97%), low microstructural damage, and homogeneous grain size. The total processing time for YAG laser sintering was 11min, which is remarkably lower than conventional sintering process in electric furnace. The radioluminescence (RL) emission of doped laser-sintered YAG ceramics were determined and their RL spectra presented the characteristic emissions of the dopants. Unexpectedly, despite the low concentration of dopants used in this work, the main emission of Tb3+ (5D4–7F5) was presented at 595nm, in the green spectral region.

Ion diffusion at the bonding interface of undoped YAG/Yb:YAG composite ceramics

Cation diffusion across a boundary between ytterbium (Yb)-doped and undoped yttrium aluminum garnet (YAG) ceramics was examined by electron microprobe analysis (EPMA). Polished Yb:YAG and undoped YAG ceramics were bonded by surface treatment with argon fast atom beam, and then heat-treated at 1400 or 1600°C for 50h or at 1400°C for 10h under vacuum. We obtained EPMA mapping images of the bonded samples that clearly showed the bulk and grain-boundary diffusion of Y and Yb ions. The number density profiles showed that the total diffusion distances of Yb and Y ions were almost equal and approximately 2 and 15μm at 1400 and 1600°C, respectively, and the dependence of diffusion distance on heating time was weak. The diffusion curves were well modeled by Harrison type B kinetics including bulk and grain-boundary diffusion. In addition, it was found that Si ions added to the samples as a sintering aid might be segregated at the grain boundary by heat treatment, and diffused only along grain boundaries.

Preparation of transparent neodymium-doped yttrium aluminate garnet (Nd:YAG) ceramics with the use of freeze granulation

This paper presents the results of the application of freeze granulation to the production of transparent neodymium-doped yttrium–aluminum garnet ceramics. Aqueous suspensions of aluminium oxide, yttrium oxide and neodymium oxide powders were prepared based on nanometric or submicronic powders which were either commercially available or prepared by precipitation. The relations between the composition of suspension, the properties of granulate and the final properties of ceramics (microstructure, optical transmission and emission spectra) were studied.