Nd3+:Y3Al5O12 laser ceramics: Influence of the size of yttrium oxide particles on sintering

The influence of the size of Y₂O₃ powder particles on the structure formation and densification of Nd³⁺:Y₃Al₅O₁₂ laser ceramics has been studied. It is shown that the use of 50- and 100-nm yttrium oxide particles makes it possible to synthesize single-phase yttrium aluminum garnet at temperatures of 1200 and 1500°C, respectively, whereas in the case of 5000-nm yttrium oxide particles 2-h exposure at a temperature of 1500°C yields only 80 wt % of the Nd³⁺:Y₃Al₅O₁₂ phase. Bulk swelling of pressed samples during sintering of 2.94Y₂O₃-0.06Nd₂O₃-5Al₂O₃ powders with the size ratio of the initial particles R(Al₂O₃/Y₂O₃) ～ 5 is observed. The application of different-sized powders (R ～ 2.5) provides quantitative ratios between phases in the 3Y₂O₃-5Al₂O₃ system at which shrinkage in a temperature range of 20–1500°C is dominant. Laser ceramics 0–2 at % Nd³⁺:Y₃Al₅O₁₂ have been obtained by the solid-phase sintering of oxide powders (R ～ 2.5). The slope efficiency for 1 at % Nd³⁺:Y₃Al₅O₁₂ laser ceramics is found to be 33%.

     

Preparation of Nd:Y3Al5O12 nanocrystals by low temperature glycol route

Y₃Al₅O₁₂, yttrium aluminum garnet (YAG) single crystals are extensively used as host materials for solid‐state lasers. The materials in nano sizes are of immense importance due to their fascinating physical and chemical properties. Nanocrystals of Nd doped YAG were synthesized by low temperature glycol route. This method consists of a mixing of nitrates in an aqueous media at reasonably low temperatures. The Nd doping concentration was optimized and kept at 2 mol%. The prepared material was annealed at different temperatures. Single phase Nd:YAG nanocrystals were obtained at 850 °C. The prepared nanocrystals were characterized by XRD, SEM and TEM techniques for the crystalline phase, crystalline size and structure. The crystalline sizes were obtained in the range of ∼20–30 nm. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Luminescence properties of Y3Al5O12:Eu3+-coated submicron SiO2 particles

Silica submicron spherical particles coated with an yttrium aluminum garnet (Y₃Al₅O₁₂, YAG) layer doped with Eu³⁺ were prepared by the sol–gel method. The structure and morphology of samples determined by the X-ray powder diffraction measurements and transmission electron microscope images, respectively, indicated that well-crystallized garnet nanocrystallites were formed with successive coating cycles. Similar trends were deduced from the evolution of the luminescence spectra. The ratio of integrated intensities of the ⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₁ transitions was used to analyze the structural variations in the surroundings of the Eu³⁺ ion. The effect of coating was analyzed by comparing the luminescence properties of the Y₃Al₅O₁₂:Eu³⁺ nanocrystalline powders and composite Y₃Al₅O₁₂:Eu³⁺/SiO₂ materials.     

Optical anisotropy associated with growth striation of yttrium garnet,Y3 (Al,Fe)5O12

The optical anisotropy associated with growth striae of yttrium garnet, Y₃(Al, Fe)₅O₁₂, was studied in terms of optical microscopy and EPMA analysis. It turned out that the lattice mismatch due to the compositional change at the growth striae gives rise to stressbirefringence. The result can be applied to compositional characterization of garnet single crystal by determining the vibration directions of polarized rays under a microscope.     

Luminescence of Y2O3:Eu and Gd2O3:Eu Depending on Precursor and Activation Temperature

The activation of Y₂O₃, Gd₂O₃and (Y_0.7,Gd_0.3)₂O₃ with Eu³⁺ ions at temperatures lower than 1000 °C is studied using different starting compounds. The activator ions are introduced during the crystallization or precipitation of the precursor. Phosphors prepared from hydroxides and activated at 900 °C exhibit luminescence with high efficiency under 254 nm Hg-line excitation. Strong emission is observed even in samples activated at 700 °C. Luminescence intensity, emission and excitation spectra are compared to these of Y₂O₃:Eu produced by the industry.     

Preparation of Y3Al5O12 nanocrystals by low temperature glycol route

Yttrium aluminum garnet, Y₃Al₅O₁₂ (YAG) nanocrystals were synthesized by low temperature glycol method. This is a modified sol–gel method performed at low temperature that consists of a mixture of salts, mostly nitrates in an aqueous media. Single phase nanocrystalline YAG was obtained at 850°C, which is much lower than others such as wet‐chemical techniques. The structural characterization is done by XRD and transmission electron microscopy. The crystallite size range from 20‐50 nm was observed for the materials prepared at 850‐ 950°C. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,morphology and structure of the dense (Y1‐xEux)2O3 spherical shape particles

The method to decrease of the porosity (densification) of crystalline spherical particles of the solid substitution solution, obtained by the method of precipitation from aqueous solution followed by low temperature crystallization of the amorphous intermediate product was proposed. The comparative analysis of morphology and structure of the particles before and after densification have been carried. It has been established that porosity of (Y_1‐xEu_x)₂O₃ particles has decreased 5 times compared to their initial state. It has been shown that densification process of the (Y_1‐xEu_x)₂O₃ spherical particles changes their morphology and structure: the size of the crystals doubles, the number and area of crystalline boundaries decrease, the intercrystalline spaces, which forming pores, are almost absent.     

Crystallization features of YBa2Cu3O7‐δ in the Y2BaCuO5‐BaCuO2‐CuO and Y2Cu2O5‐BaCuO2 systems

Based on the data of X‐ray phase and microstructure analysis, the sample composition was optimized in order to provide maximum size of the textured macrograins of YBa₂Cu₃O_7‐δ and of the crystallites in the Y₂BaCuO₅‐BaCuO₂‐CuO, Y₂Cu₂O₅‐BaCuO₂ systems. The growth rate has been studied and the YBa₂Cu₃O_7‐δ growth activation energy has been calculated for the samples of Y₂BaCuO₅+3BaCuO₂+2.3CuO, Y₂BaCuO₅+3BaCuO₂+0.6CuO, and Y₂Cu₂O₅+3.5BaCuO₂ compounds in the temperature range of 1240‐1270K for the case of use of the Y₂Cu₂O₅ and Y₂BaCuO₅ precursors with an average grain diameter of 10 μm and 1mm. A crystallization mechanism of YBa₂Cu₃O_7‐δ in the Y₂BaCuO₅‐BaCuO₂‐CuO and Y₂Cu₂O₅‐BaCuO₂ systems in the case of different sizes of Y₂BaCuO₅ and Y₂Cu₂O₅ precursor grains was proposed and validated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural inhomogeneity and properties of Y3Fe5O12 crystals with allowance for their crystallographic orientation

The character of nonuniform distribution of the main cations Y and Fe in the plane of samples of yttrium garnet Y₃Fe₅O₁₂ and the nonstatistical incorporation of process impurities along the crystallographic directions [110], [111], and [100] are investigated. The structural inhomogeneity revealed in the samples is discussed with allowance for the difference in the growth rates of the garnet crystal faces under study, specific features of the incorporation of dominant impurities, and the relationship between this inhomogeneity and the optical and kinetic properties of the crystals.     

Refractive indices of laser nanocrystalline ceramics based on Y3Al5O12

Refractive indices of the nanocrystalline Y₃Al₅O₁₂ ceramic and a garnet single crystal of the same composition have been measured. In the visible and near IR range (0.4–1.064 μm), the prism method was used; in the medium IR range (2–6.2 μm), the interference method with the use of thin plates was applied. The refractive indices of these crystalline materials are practically the same over the entire spectral range studied and are described by the approximate formula proposed earlier for a single crystal. The parameters of the continuos-wave lasing in the nanocrystalline Y₃Al₅O₁₂ ceramic doped with Nd³⁺ and Yb³⁺ ions measured recently are presented.     

On the Existence and Formation of Y4Al2O9

For the preparation and transformation sequence in the system Y₄O₃–Al₂O₃ the sintering of homogeneously mixed oxide powders was chosen. The constituents of the Y₄Al₂O₉ phase were determined by quantitative phase analysis with the method of inner standards. Corresponding gauge curves for the conditions of the temperatures of sintering were drawn. At low temperatures appears as first in the whole molar range the (2:1) phase, i.e. Y₄Al₂O₉. With increasing temperature and sintering time the yield of this mixed crystal phase depends on the concentration of the oxide components in the powder mixture of the start materials. In flux mixtures of the components PbO, PbF₂, and B₂O₃ and despite suitable nucleation it was not possible to obtain this compound. In the melt the compound Y₄Al₂O₉ was prepared frequently in near molar conditions. Also a glass was prepared with (2:1) stoichiometry. Single crystals were identified by X-rays.     

Specific heats of FCC solid solutions of the Bi2O3-Y2O3 system

For the first time specific heats of the face centered cubic solid solutions (Bi₂O₃)_1−x(Y₂O₃)_x in the temperature range 350–1000 K were measured by means of Differential Scanning Calorimetry. Samples were also investigated with thermal expansion. The results showed the phase transitions for (Bi₂O₃)_0.75 (Y₂O₃)_0.25, which is acsribed to δ → δ* change in lattice mentioned in literature and for (Bi₂O₃)_0.58(Y₂O₃)_0.42, which is connected with a metastable behaviour of this sample.     

New data on the physical properties of Y3Al5O12-based nanocrystalline laser ceramics

Microhardness and fracture toughness of highly transparent Y₃Al₅O₁₂-and Y₃Al₅O₁₂: Nd³⁺-based nanocrystalline ceramics are measured for the first time. For the Y₃Al₅O₁₂: Nd³⁺ laser ceramics, the use of a longitudinal scheme with a diode-laser pumping at a wavelength of 1.3186 mm (⁴ F _3/2 → ⁴ I _13/2 channel) enabled one to attain an output power of continuous-wave lasing of ～3.7 W with 35% efficiency.     

The luminescence of Pr3+ ions doped in Y4Al2O9 by sol–gel synthesis

The Pr³⁺-doped Y₄Al₂O₉ powders were synthesized by sol–gel method. Powder X-ray diffraction and SEM techniques were used to check for Y₄Al₂O₉ powders. The Li⁺ co-doping with Pr³⁺ has an influence on the sintering temperature and morphology of the Y₄Al₂O₉ powders produced from the gel. The emission spectra under different excitations, e.g., the 488 nm line of an argon-ion laser, X-ray and UV light, were investigated. The luminescence intensity of Y₄Al₂O₉:Pr³⁺ could be increased with Li⁺ co-doping. Luminescence properties of Pr³⁺ ions in the two samples have some difference. In the Y₄Al₂O₉:Pr³⁺, the emission at 490 nm from ³P₀ is dominant, while, the Y₄Al₂O₉:(Pr³⁺ + Li⁺) system was characterized by a red emission at 607 and 610 nm corresponding to the ¹D₂ → ³H₄ inner transition of Pr³⁺ ions; and these two emissions show different excitation band from the 4f5d state.     

Lasing and refractive indices of nanocrystalline ceramics of cubic Yttrium Oxide Y2O3 doped with Nd3+ and Yb3+ ions

A continuous-wave lasing at 1 μm was excited by the radiation of semiconductor laser diodes at room temperature in nanocrystalline ceramics Y₂O₃ doped with Nd³⁺ and Yb³⁺ ions. The refractive indices of the undoped nanocrystalline Y₂O₃ ceramics were measured in the wavelength range 0.4–9 μm.     

Y2O3-Al2O3-Nd2O3 phase diagram and the growth of (Y,Nd)3 Al5O12 single crystals

The optimum compositions of the melts used for the growth of yttrium-aluminum garnet (YAG) single crystals with different neodymium contents are determined using the phase diagram of the ternary system Y₂O₃-Al₂O₃-Nd₂O₃ with the binary sections Y₃Al₅O₁₂-Nd₂O₃ and Y₃Al₅O₁₂-Nd₃Al₅O₁₂. A number of melt compositions characterized by one garnet phase, namely, (Y,Nd)₃Al₅O₁₂, are established. Single crystals of yttrium-aluminum garnets with a high content of the activator (up to 2.6 wt % Nd) are grown by the Czochralski method. __________ Translated from Kristallografiya, Vol. 48, No. 5, 2003, pp. 945–949. Original Russian Text Copyright ? 2003 by Soboleva, Chirkin. Dedicated to the 60th Anniversary of the Shubnikov Institute of Crystallography of the Russian Academy of Sciences     

Production and shaping of high performance phosphors by using the sol–gel process: Yttrium aluminum garnet (Y3Al5O12)

Luminescent Y₃Al₅O₁₂:Tb³⁺ (YAG:Tb³⁺) phosphor thin films and powders have been successfully prepared by the sol–gel route from alkoxide precursors. Advanced coatings were produced by spray and dip-coating from stabilized sols. X-ray diffraction (XRD), attenuated total reflectance/Fourier transform infrared spectroscopy (ATR/FTIR) and atomic force microscopy (AFM) were used to investigate the structure and morphology of layers. YAG phases of high purity were obtained for both powders and films. AFM study revealed coatings of homogeneous topography, whatever the deposition technique. However, dip-coated samples exhibited a much smoother topography, characterized by a root mean square (rms) roughness much lower than that of spray-coated ones. Laser induced emission spectra and decay times of Tb³⁺ ions in a spray-coated film were recorded. Measurements exhibit the characteristic green emission of Tb³⁺. Effectiveness of the Tb³⁺ doped coatings under UV excitation is also illustrated by pictures.     

Growth studies of YVO4 crystals (II). Changes in Y?V?O-stoichiometry

Incongruent vanadium oxide vaporization of yttrium orthovanadate (YVO₄) melt generates changes in both oxygen and yttrium-vanadium (Y V) stoichiometry. Slightly modified YVO₄ or YVO₄ + Y₈V₂O₁₇ phases are formed from continuously changing melt systems depending on their starting compositions. The occurrence of Y₈V₂O₁₇ in yttrium orthovanadate crystal fibers grown by laser heated pedestal growth (LHPC) technique can be simply eliminated by utilization of suitable V₂O₅-excess starting compositions. In contrast, the oxygen-deficient YVO_4–x black phase is an inherently oxygen deficient phase with limited solid solution in the YVO₄ YVO₃ subsystem of Y₂O₃ V₂O₅ V₂O₃ complex ternary phase diagram close to the congruent YVO₄ composition (49.3 mol% V₂O₅–50.7 mol% Y₂O₃). The greater oxygen deficiency YVO_4–x specimens have smaller lattice parameters as determined from detailed XRD data. Ceramic feed rod and fiber crystal grown from the feed rod with slight yttrium oxide excess starting composition were characterized by electron microprobe analysis. Changes in both Y V and oxygen stoichiometry were observed along the fiber, due to double limited solid solution system of three dimensional ternary phase diagram. Consequently, both the presence of Y₈V₂O₁₇ phase and change of Y V stoichiometry over oxygen deficiency cause difficulties for YVO₄ crystal growth from yttrium oxide excess melt.     

Effects of yttrium codoping on fluorescence lifetimes of Er3+ ions in SiO2–Al2O3 sol–gel glasses

In order to find a new glass host and optimize erbium doping for IR glass optical amplifiers in photonic applications, a study on the optimization of the emission of erbium ions in the SiO₂–Al₂O₃ glass by codoping with Y₂O₃ is performed. It is first attempted to make a new sol–gel glass host based on SiO₂, Al₂O₃, and Y₂O₃ doped with Er³⁺ ions of the composition (1−x)SiO₂–xAl₂O₃–yY₂O₃:0.65Er₂O₃ (in mol%), x varies from 0 to 65, and y from 0 to 4. The optimal proportion in mol% of SiO₂ and Al₂O₃ for the Er³⁺ emission (at a fixed optimal concentration of 0.65) was 65 – 35. The effect of Y₂O₃ content on photoluminescence, decay curve profiles and lifetime of the ⁴I_13/2 level of Er³⁺ in SiO₂–Al₂O₃ glass is observed. The largest quantum efficiency and the higher emission intensity are observed in the sample with 65Al₂O₃ and 4Y₂O₃. The emission intensity at 1530 nm is two times higher than in glasses without Y₂O₃. A shift of 3 nm to shorter wavelengths is observed. The emission spectral profiles are flatter and broader for the glasses containing Al and Y (bandwidth of 59.5 nm). The decay curves show strong difference profiles for the different samples. The increase of the lifetime value τ (about ms) of the ⁴I_13/2 level of Er³⁺ in the SiO₂–Al₂O₃ with the Y₂O₃ is discussed.     

Colour Centre in Nd3+-doped Yttrium Aluminates

Spectroscopic and laser properties of YAG:Nd and YAP:Nd grown from the nonstoichiometric melts or those containing Mo and Fe impurity were compared. YAG:Nd grown from the melt with surplus of Y₂O₃ and annealed in H₂ at ∼ 1400 °C have an increased laser performance. Mo admixture in hydrogen annealed YAP:Nd laser crystals suppresses effectively the detrimental action of iron impurity.