Effect of Yttrium and Erbium Ions on Epitaxial Phase Transformations in Alumina

The effect of low concentrations of Y, Er, and Cr solutes on the amorphous-to-γ transformation and on the γ-to-α transformation in aluminum oxide has been studied in situ by time-resolved reflectivity. The activation energies of the two transformations with these dopants are the same as in undoped alumina, being 4.1 ± 0.1 and 5.2 ± eV, respectively. Although not affecting the activation energies, Y, Er, and Cr do affect the transformation kinetics. Y and Cr ions decrease the γ-to-α transformation velocity and, over the limited range studied, do so in proportion to their concentration. Concentrations of Er as low as ∼6 ppm retard the γ-to-α transformation and concentrations of 32 ppm essentially stop the transformation occurring within the times and temperatures accessible within the present experiment, thereby preventing quantification of the effect of Er on the α-phase transformation. Erbium also retards the amorphous-to-γ transformation relative to undoped alumina whereas yttrium and chromium accelerate it.     

Effect of Composition and Crystallization Temperature on Microstructure of Y- and Er-SiAlON Iw-Phase Glass-Ceramics

Glass-ceramics were produced from Y- and Er-SiAlON compositions containing the I_w phase as the only detectable crystalline phase. TEM analysis showed that these materials had fine-scale glass-ceramic microstructures with crystallite sizes <1 μm and glass contents between 20% and 40%, depending on the starting powder composition: Increased yttrium or erbium content of the starting material resulted in a reduced glass content. The I_w-phase crystals in all specimens were found by EDX analysis in TEM to display a solid-solution range with a clear anticorrelation between the yttrium or erbium content and the silicon content: A possible explanation for this effect was suggested. The average crystal composition approximated a cation ratio of Y:Si:Al = 3:2:1. The composition of the residual glass was also similar in all specimens. Some small silicon-rich amorphous features were found in the microstructures, and it was believed that these had occurred because of phase separation in the glass during the crystallization process.     

Spectroscopic Properties of Er3+-Doped Na2O–La2O3–Al2O3–SiO2 Glasses

Er³⁺-doped sodium lanthanum aluminosilicate glasses with compositions of (90− x )(0.7SiO₂·0.3Al₂O₃)· x Na₂O·8.2La₂O₃· 0.6Er₂O₃·0.2Yb₂O₃·1Sb₂O₃ (in mol%) ( x = 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ω _t ( t = 2, 4, 6) decreases with increasing Na₂O. Ω₂ decreases rapidly with increasing Na₂O while Ω₄ and Ω₆ decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na₂O. Fluorescence spectra of the ⁴ I _13/2 to ⁴ I _15/2 transition have been measured and the change with Na₂O content is discussed. It is found that the full width at half-maximum decreases with increasing Na₂O.     

Synthesis of GAGG:Ce3+ powder for ceramics using mechanochemical and solution combustion methods

Gadolinium aluminum gallium garnet doped with cerium (Gd_2.99Al_2.00Ga_3.00O_12.00:Ce_0.01, or GAGG:Ce) powders has been synthesized with high‐energy ball milling (HEBM) and solution combustion synthesis (SCS) techniques. The structures and morphologies of the powders were characterized through use of powder X‐ray diffraction (PXRD), photoluminescence (PL) measurements, dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV‐decay time measurements. Changes in the mechanochemically produced powders were monitored over time, while the solution combustion synthesis of GAGG:Ce was conducted using various ratios and types of fuels. In both production methods, particle sizes on the order of microns gave evidence of agglomeration.     

Near-Field Optical Characterization of Nanocomposite Materials

We present a near-field optical technique which makes use of the strongly enhanced optical field at a laser-illuminated metal tip. The enhanced field is used to locally excite the sample under investigation by multiphoton absorption. An optical scan image with spatial resolutions down to 20 nm is established by detecting the emitted fluorescence. The principle of the method is described and experimental results are demonstrated for samples of J-aggregates of PIC dye molecules. Ongoing experiments on nanocomposite, Er³⁺-doped oxyfluoride glass-ceramics are discussed.     

Complement to “Optical and Judd-Ofelt spectroscopic study of Er3+-doped strontium gadolinium gallium garnet single-crystal”

In the previous paper “Optical and Judd-Ofelt spectroscopic study of Er³⁺-doped strontium gadolinium gallium garnet single-crystal” (J Am Ceram Soc. 2019;102:873–878), we have reported optical and Judd-Ofelt spectroscopic properties of Er³⁺-doped strontium gadolinium gallate (SrGdGa₃O₇) single-crystal, and the Judd-Ofelt study was performed on the basis of unpolarized absorption spectrum of the crystal. Present work reports the corrected unpolarized absorption spectrum and Er³⁺ concentration in the crystal, and hence corrected Judd-Ofelt spectroscopic properties and cross-section data. In addition, the polarization effect was considered in the Judd-Ofelt analysis on the basis of polarization-resolved absorption spectra. Effective Judd-Ofelt parameters are presented and discussed in comparison with the results from the unpolarized spectrum, and consistent results have been obtained. This study also considers the effects of some other factors on the Judd-Ofelt parameters. These include Er³⁺ concentration and selection of Er³⁺ absorption bands for the Judd-Ofelt analysis.     

Incorporation of Er3+ into BaTiO3

The incorporation of Er³⁺ into BaTiO₃ ceramics was investigated on samples containing 0.25, 0.5, 1, 2, 8, and 10 at.% of dopant, after sintering at 1350–1550°C in air. For Er³⁺ concentrations ≤1 at.%, dense and large-grained ceramics with low room-temperature resistivity (10²–10³Ω·cm) were obtained. The observed properties are largely independent of stoichiometry. Simultaneous substitution of Er³⁺ at both cation sites, with higher preference for the Ba site, is proposed. The behavior of heavily doped ceramics depends on stoichiometry. When Ba/Ti < 1, the electrical properties change from slightly semiconducting to insulating as Er concentration increases from 2 to 8 at.%. The ceramics have tetragonal perovskite structure and contain a large amount of Er₂Ti₂O₇ pyrochlore phase. On the other hand, when Ba/Ti > 1, the ceramics are insulating, fine-grained, and single phase. In this case, incorporation of Er³⁺ predominantly occurs at the Ti site, with oxygen vacancy compensation. Incorporation is accompanied by a significant reduction of tetragonality and by expansion of the unit cell. The different results indicate that Er³⁺ solubility at the Ba site does not exceed 1 at.%, whereas solubility at the Ti site is at least 10 at.%. However, the incorporation of Er³⁺ and the resulting properties are also strongly affected by sintering conditions.     

Vibrational Spectra of Water- and Ammonium-Chloride-Related Residues and Upconversion Fluorescence of Er3+ in ZnCl2-Based Glasses

Chloride glasses of the ZnCl₂ and 20KCl-20BaCl₂-60ZnCl₂-0.5ErCl₃ systems were prepared using NH₄Cl as a dehydrating and chlorinating agent, under the melt-quenching method. Water- and ammonium-chloride-related residues in ZnCl₂ glasses were investigated by infrared and near-infrared absorption spectra. Water, Zn—OH, ClO, ClO₂⁻, Zn²⁺-coordinated water, free NH₃, NH₄⁺, and Zn²⁺-coordinated NH₃ were identified in ZnCl₂ glasses. 20KCl-20BaCl₂-60ZnCl₂-0.5ErCl₃ glasses prepared by melting at 500°C for 20 min, under reduced pressure, contained the smallest amounts of water, Zn—OH, and Zn²⁺-coordinated NH₃ and showed strong Er³⁺ upconversion fluorescence.     

Heat-Resistant Silicon Carbide with Aluminum Nitride and Erbium Oxide

Fully dense SiC ceramics with high strength at high temperature were obtained by hot-pressing and subsequent annealing under pressure, with AlN and Er₂O₃ as sintering additives. The ceramics had a self-reinforced microstructure consisting of elongated SiC grains and a grain-boundary glassy phase. The strength of these ceramics was ∼550 MPa at 1600°C, and the fracture toughness was ∼6 MPa·m^1/2 at room temperature. The beneficial effect of the new additive composition on high-temperature strength might be attributable to the introduction of aluminum from the liquid composition into the SiC lattice, resulting in a refractive grain-boundary glassy phase.     

Glass-forming regions and enhanced 2.7 μm emission by Er3+ heavily doping in TeO2–Ga2O3–R2O (or MO) glasses

Er³⁺-doped fiber lasers operating at 2.7 μm have attracted increasing interest because of their various important applications; however, the intrinsic self-terminating effect of Er³⁺ and the reliability of glass hosts hindered the development of Er³⁺-doped fiber lasers. Herein, the glass-forming regions of a series TeO₂–Ga₂O₃–R₂O (or MO) (R = Li, Na, and Rb; M = Mg, Sr, Ba, Pb, and Zn) glasses are predicted by the thermodynamic calculation method. On this basis, the physical and optical properties of TeO₂–Ga₂O₃–ZnO (TGZ) glass are investigated in detail as an example. Under the excitation of 980 nm laser diode, the fluorescence intensity at 2.7 μm reaches a maximum in the heavily Er³⁺-doped TGZ glass. By contrast, the accompanying near-infrared fluorescence at 1.5 μm and upconversion green emissions at 528 nm and 546 nm are all effectively weaken. Furthermore, the lifetime gap between the ⁴I_11/2 upper laser level and ⁴I_13/2 lower laser level is sharply narrowed from 2.81 ms to 0.59 ms, which is beneficial to overcome the population conversion bottleneck. All results demonstrate that these newly developed ternary tellurite glass systems are promising candidates for near-/mid-infrared laser glass fiber, fiber amplifiers, and fiber lasers.     

Microwave-Assisted Combustion Synthesis of Tantalum Nitride in a Fluidized Bed

Combustion synthesis experiments in a fluidized bed have been conducted using nitrogen as the fluidizing gas for the formation of transition-metal nitrides that are potential replacements for traditional hydrodenitrogenation and hydrodesulfurization catalysts. The microwave-assisted ignition of reaction has been investigated for its potential to produce nitride overlayers on two different sizes of tantalum particle substrates. Various characterization techniques—X-ray diffractometry, energy dispersive spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy—have been used to study the presence of nitride overlayers. The results indicate that microwave assistance can permit controlled formation of tantalum nitride (Ta₂N) overlayers.     

Nonlinear negative transmittance at a CW 980‐nm laser diodes pumping in Yb3+:CaF2 nanocrystals‐embedded glass ceramics

Cooperative upconversion luminescence (CUCL) occurs in spectral regions in which single ions do not have energy levels. However, all results reported so far are concentrated on luminescence properties from Yb³⁺ ions‐doped various hosts. Here, we report the observation of nonlinear negative transmittance (NNT) at continuous‐wavelength (CW) 980‐nm laser diodes (LDs) pumping in silicate oxyfluoride glass ceramics (GCs)‐containing CaF₂:Yb³⁺ nanocrystals. The unique optical nonlinearity is analyzed based on energy‐level transitions, dynamic evolution, rate equation, and power transmission equation, which can be explained as the cooperative optical absorption for the intense CUCL of Yb³⁺ ions. The NNT in the CaF₂:Yb³⁺ nanocrystals‐embedded GCs can be tailored with the power of a CW 980‐nm LDs, which possesses potential for the development of future optical limiters and switches.     

Rare‐earth‐doped SiO2‐CaF2 glass ceramic nano‐particle with upconversion properties

Rare‐earth‐doped upconversion nano‐phosphor shows new possibilities in the field of bioimaging because of its unique properties like higher penetration depth, low signal to noise ratio (SNR), good photo stability, and zero auto fluorescence. The oxyfluoride glass system is the combination of both fluoride and oxide where fluoride host offers high optical transparency due to low phonon energy and oxide network offers high physical stability. Thus, in the present work, an attempt has been made to synthesize 1 mol% Er³⁺ doped SiO₂‐CaF₂ glass ceramic nano‐particles through sol‐gel route. The synthesized glass ceramic particles were heat treated at 4 different temperatures starting from 600°C to 900°C.The X‐ray diffraction (XRD) analysis and Transmission electron microscopy (TEM) analysis confirmed the formation of CaF₂ nano‐crystals in the matrix which is 20‐30 nm in size. The vibrational spectroscopic analysis of the glass ceramics sample has been investigated by Fourier transform infrared (FTIR) spectroscopy. The UV‐Visible‐NIR spectroscopy analysis was carried out to analyze the absorption intensity in the near infrared region. Upon 980 nm excitation, the sample shows red emission corresponds to ⁴F_9/2→⁴I_15/2 energy level transition. The prepared nano‐particles showed excellent biocompatibility when tasted on MG‐63 osteoblast cells.     

Er3+掺杂氧氟锗硅酸盐玻璃的频率上转换研究

研究了基质玻璃成分对Er^3 掺杂氧氟锗硅酸盐玻璃上转换光谱和Raman光谱的影响,分析了氧氟锗硅酸盐玻璃中Er^3 的上转换发光机理。结果表明：通过975nm的激光二极管激发,在室温下同时观察到强烈的绿光(529,545nm)和红光(657nm)发射,分别是由于Er^3 的。H11/2→^4I15/2,^4S3/2→^4I15/2,和^4F9/2→^4I15/2跃迁,且均为双光子吸收过程。与545nm的绿光发射相比,657nm的红光发光强度比较微弱。随GeO2浓度的增加,基质玻璃的最大声子能量下降,导致无辐射跃迁几率降低,因此绿光和红光的发光强度都增强,但是其对绿光的影响大于红光。     

Yb3+/Er3+共掺碲钨酸盐玻璃的能量传递与频率上转换发光

在970nm LD激发和Er^3 离子浓度几乎不变情况下,研究了Yb^3 ／Er^3 共掺碲钨酸盐玻璃中的能量传递和其上转换发光特性。结果表明：随掺Yb^3 浓度的增加,Yb^3 ／Er^3 间能量传递效率也增加,其值在0．52到0．60之间。在Yb^3 ／Er^3 共掺碲钨酸盐玻璃中观察到峰值分别位于533,547nm和668nm的上转换绿光和红光,它们分别来源于Er^3 离子^2H11/2→^4I15／2(533nm),^4S3／2→^4I15／2(547nm)和^4F9/2→^4I15／2(668nm)辐射跃迁。上转换红光和绿光均为双光子过程,且随Yb^3 离子掺杂浓度的增加,上转换红绿光强度和其强度比值Ic／Ig也增加,这被认为是与激发态Er^3 与激发态Yb^3 之间的能量传递过程有关。