Fabrication and characterization of highly transparent Er:Y2O3 ceramics with ZrO2 and La2O3 additives

In this study, we report highly transparent Er:Y₂O₃ ceramics (0–10 at% Er) fabricated by a vacuum sintering method using compound sintering additives of ZrO₂ and La₂O₃. The transmittance, microstructure, thermal conductivity and mechanical properties of the Er:Y₂O₃ ceramics were evaluated. The in-line transmittance of all of the Er:Y₂O₃ ceramics (1.2 mm thick) exceeds 83% at 1100 nm and 81% at 600 nm. With an increase in the Er doping concentration from 0 to 10 at%, the average grain size, microhardness and fracture toughness remain nearly unchanged, while the thermal conductivity decreases slightly from 5.55 to 4.89 W/m K. A nearly homogeneous doping level of the laser activator Er up to 10 at% in macro-and nanoscale was measured along the radial direction from the center to the edge of a disk specimen, which is the prominent advantage of polycrystalline over single-crystal materials. Based on the finding of excellent optical and mechanical properties, the compound sintering additives of ZrO₂ and La₂O₃ are demonstrated to be effective for the fabrication of transparent Y₂O₃ ceramics. These results may provide a guideline for the application of transparent Er:Y₂O₃ laser ceramics.     

Fabrication and properties of transparent Tb:YAG fluorescent ceramics with different doping concentrations

Terbium doped yttrium aluminum garnet (Tb:YAG) transparent ceramics with different doping concentrations were fabricated by the solid-state reaction method using commercial Y₂O₃, α-Al₂O₃ and Tb₄O₇ powders as raw materials. Samples sintered at 1750 °C for 20 h were utilized to observe the optical transmittance, microstructure and fluorescence characteristics. It is found that all the Tb: YAG ceramics with different doping concentrations exhibit homogeneous structures with grain size distributions around 22–29 µm. For the 5 at% Tb:YAG transparent ceramics, the grain boundaries are clean with no secondary phases. The photoluminescence spectra show that Tb:YAG ceramics emit predominantly at 544 nm originated from the energy levels transition of ⁵D₄→⁷F₅ of Tb³⁺ ions, and the intensity of the emission peak reaches a maximum value when the Tb³⁺ concentration is 5 at%. The in-line transmittance of the 5 at% Tb:YAG ceramics is 73.4% at the wavelength of 544 nm, which needs to be further enhanced by optimizing the fabrication process. We think that Tb:YAG transparent ceramics may have potential applications in the high-power white LEDs.     

Coating Y2O3 nano-particles with ZrO2-additive via precipitation method for colloidal processing of highly transparent Y2O3 ceramics

In the present work, transparent Y₂O₃ ceramics were prepared via colloidal processing method using ZrO₂-coated nano-sized Y₂O₃ powders. The chemical precipitation method was adopted for the coating of Y₂O₃ raw powder. The evolution of the coated-ZrO₂ layer upon calcination was studied. The rheological behaviors of the slurries of Y₂O₃ powders coated with different content of ZrO₂-additive were investigated. The pH_IEP of ZrO₂-coated Y₂O₃ powders shows intermediate values between that of raw Y₂O₃ and ZrO₂ powders. As the ZrO₂-coating concentration increased from 0 to 5.0 at%, the magnitude of the negative zeta potential at pH > pH_IEP shows a general trend of increment, whereas it decreased at pH < pH_IEP. The viscosity decreases pronouncedly with the increase of ZrO₂ content from 0.5 at% to 3.0 at%. The suspensions with low viscosity and high stability was achieved for a solid loading of 35.0 vol% using Y₂O₃ powders coated with 5.0 at% ZrO₂. The dispersed suspensions were consolidated by centrifugal casting method and the green bodies shown improved homogeneity. Transparent Y₂O₃ ceramics were fabricated by vacuum sintering at 1800 ℃ for 5 h. Transmittance at wavelength 800 nm (1.0 mm thick) reached 80.8%, close to the theoretical value of Y₂O₃.     

The absorption and emission properties of highly transparent ZrO2-doped Yb3+: Y2O3 ceramics

Ultra-highly transparent ZrO₂-doped Yb³⁺: Y₂O₃ ceramics were prepared by slip casting and vacuum pressureless sintering and the transmittance reached the highest value of 80.9% for the sample doped with 8.0 at% Yb³⁺. There are three main absorption peaks at 905, 950, and 976 nm, corresponding to the transition from the lowest level of field splitting of ²F_7/2 crystal to every splitting energy levels of ²F_5/2 crystal field. We analyzed the absorption and emission spectra of transparent Yb³⁺: Y₂O₃ from the energy level structure of Yb³⁺, and the transmission, absorption, and emission spectra were systematically studied. There are three main absorption peaks at 905, 950, and 976 nm and four emission peaks at 1076, 1031, 1013, and 977 nm, respectively. The emission peaks at 977 and 1013 nm broaden and vanish for 8.0 and 10.0 at% Yb³⁺-doped Y₂O₃, which may be related to the change of Y₂O₃ crystal field caused by high concentration.     

Fabrication and magneto-optical property of yttria stabilized Tb2O3 transparent ceramics

(Tb_0.5Y_0.5)₂O₃ transparent ceramics have been prepared by wet chemical co-precipitation route and flowing H₂ atmosphere sintering. The optical quality, microstructure and magneto-optical properties of the ceramics were investigated. No sintering aids or milling were adopted in the ceramic fabrication processing. The cold isostatic pressed green compact could be sintered to be transparent (Tb_0.5Y_0.5)₂O₃ ceramic at 1800 ℃ in flowing H₂ atmosphere. The mechanical polished ceramic showed the good transmittance from visible to near infrared wavelength, corresponding to a 71.9% transmittance at 1400 nm wavelength. The Verdet constant measured at 632.8 nm of the (Tb_0.5Y_0.5)₂O₃ transparent ceramics was -220.19 rad T⁻¹ m^-1, which was 1.64 times that of Tb₃Ga₅O₁₂ single crystal.     

Highly transparent Yb:Y2O3 ceramics obtained by solid-state reaction and combined sintering procedures

(Y_0.87-xLa_0.1Zr_0.03Yb_x)₂O₃ (x?=?0.02, 0.04, 0.05) transparent ceramics were obtained by solid-state reaction and combined sintering procedures with La₂O₃ and ZrO₂ as sintering additives. A method based on two-step intermediate sintering in air followed by vacuum sintering was applied in order to control the densification and grain growth of the samples during the final sintering process. The results indicate that La₂O₃ and ZrO₂ co-additives can improve the microstructure and optical properties of Yb:Y₂O₃ ceramics at relatively low sintering temperature. On the other hand, the addition of Zr⁴⁺ ions leads to the formation of dispersed scattering volumes in the ceramic bodies. Transmittance of 78.8% was measured for the 2.0?at% Yb:Y₂O₃ ceramic sample at the wavelength of 1100?nm. The spectroscopic properties of Yb:Y₂O₃ ceramics were investigated at room temperature. The obtained results show that the absorption cross-section at 978?nm is in the range of 2.08?×?10^–20 to 2.36?×?10^–20 cm², whereas the emission cross-section at 1032?nm is ~1.0?×?10^–20 cm².     

Preparation and luminescent properties of highly transparent Y3Ga5O12:M3+ (M = Dy,Cr) ceramics

YGG:Dy and YGG:Cr polycrystalline ceramics were prepared via a solid-state reaction-two step sintering approach. The crystalline structure, phase evolution, morphologies and luminescence properties of as prepared transparent ceramics were intensively investigated. In-line transmittance of YGG:Dy and YGG:Cr transparent ceramics can reach up to 70.6% and 67.3% at 1200 nm, respectively. For YGG:Dy transparent ceramic, three emission bands centered at 492 nm, 581 nm and 669 nm can be observed under excitation of 353 nm. Its CIE color coordinate is (0.3182, 0.3326) under UV irradiation, which is a promising UV-converting candidate for WLEDs. While the emission peak of YGG:Cr transparent ceramic is at about 709 nm, which can be one of the candidate materials applied in red-emitting LEDs with excellent color rendering index. The experimental results demonstrate that Y₃Ga₅O₁₂:M³⁺ (M = Dy, Cr) transparent ceramics are promising novel luminescent materials for LEDs.     

Structural and Thermo‐Mechanical Properties of Nd: Y2O3 Transparent Ceramics

Various content of neodymia Nd: Y₂O₃ (Nd: 0.5–5.0 at.%) transparent ceramics were fabricated by vacuum sintering. The prepared Nd: Y₂O₃ ceramics exhibit high transmittance (~80%) at the wavelength of 1100 nm. It is found that the increase in Nd concentration enhances the grain size growth, while decreases the phonon energy, which is benefit for improving both the luminescence quantum and up‐conversion efficiency. The thermal conductivity and thermal expansion coefficient of the transparent 1.0 at.% Nd: Y₂O₃ ceramic is 5.51 W·(m·K)^?1 and 8.11 × 10^?6 K^?1, respectively. The hardness and the fracture toughness of the transparent ceramic is 9.18 GPa and 1.03 Mpa·m^1/2, respectively. The results indicate that the Nd: Y₂O₃ transparent ceramic is a potential candidate material for laser.     

Effects of ZrO2 on the photoluminescence of 0.5 at% Eu:(Y0.9La0.1)2O3 transparent ceramics

Zr-codoped 0.5 at% Eu: (Y_0.9La_0.1)₂O₃ ceramics sintered in H₂-reducing atomsphere, together with the ceramics with annealing treatment, were fabricated by solid-state reactions and the effects of Zr codoping on these materials’ photoluminescence examined. The obtained emission spectra showed that Zr codoping adjust the materials’ photoluminescence with UV excitation and a logical explanation was proposed. The results suggested that an Eu-doped, yttrium-lanthanum oxide transparent ceramic with Zr in low concentration appeared to have promising potential in modern lighting applications.     

Fabrication of transparent yttria ceramics by alcoholic slip-casting

Y₂O₃ transparent ceramics were prepared from alcoholic slurries of Y₂O₃ nanopowders via a slip-casting method to avoid the hydrolysis issue. Polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG) and polyethylenimine (PEI) were used as dispersants to improve the rheological properties of the slurries. It was found that PEI is the most effective dispersant in ethanol. The adsorbed amount of PEI was evaluated by infrared absorption and rheology measurements. Y₂O₃ slurry with a solid loading of 20.8 vol% and a viscosity of <0.1 Pa s at the shear rate of 10 s⁻¹ was obtained using 1.5 wt% PEI. The slurry yielded a homogeneous green body, and finally resulted in a high-quality Y₂O₃ ceramic with the in-line transmittance of 80% at 800 nm.     

Fabrication of Er:Y2O3 transparent ceramics for 2.7 μm mid-infrared solid-state lasers

Laser grade 7 at.% Er:Y₂O₃ transparent ceramics with submicron grain size were fabricated by using one-step vacuum sintering followed by hot isostatic pressing (HIPing) technique. Through studying the sintering trajectory of Er:Y₂O₃ ceramics, the sintering temperature zone where sufficient relative density (>96%), no pore-boundary separation, and sub-micron grain size (<1 μm) ceramic samples could be identified. The samples pre-sintered in this zone were readily densified by HIPing. To maximum the densification and achieve high transparency, it is critical to suppress the final-stage grain growth. After HIPing at 1520 °C, the Er:Y₂O₃ ceramics were fully densified without further grain growth, and exhibited in-line transmission of about 81.6% at 2000 nm. Continuous wave (CW) room temperature laser operation of the Er:Y₂O₃ transparent ceramic at 2.7 μm was demonstrated.     

Fabrication,microstructure and spectroscopic properties of Yb:Lu2O3 transparent ceramics from co-precipitated nanopowders

Ytterbium doped lutetium oxide (Yb:Lu₂O₃) transparent ceramics were fabricated by vacuum sintering combined with hot isostatic pressing (HIP) of the powders synthesized by the co-precipitation method. The effects of calcination temperature on the composition and morphology of the powders were investigated. Fine and well dispersed 5?at% Yb:Lu₂O₃ powders with the mean particle size of 67?nm were obtained when calcined at 1100?°C for 4?h. Using the synthesized powders as starting material, we fabricated 5?at% Yb:Lu₂O₃ ceramics by pre-sintering at different temperatures combined with HIP post-treatment. The influence of pre-sintering temperature on the densities, microstructures and optical quality of the 5?at% Yb:Lu₂O₃ ceramics was studied. The ceramic sample pre-sintered at 1500?°C for 2?h with HIP post-treating at 1700?°C for 8?h has the highest in-line transmittance of 78.2% at 1100?nm and the average grain size of 2.6?µm. In addition, the absorption and emission cross sections of the 5?at% Yb:Lu₂O₃ ceramics were also calculated.     

Structural and optical properties of Tm:Y2O3 transparent ceramic with La2O3, ZrO2 as composite sintering aid

The paper reports the use of La₂O₃ and ZrO₂ co-doping as a composite sintering aid for the fabrication of Tm:Y₂O₃ transparent ceramics. Two groups of experiments were conducted for investigating the influences of composite sintering aids on the microstructures and the optical properties of Tm:Y₂O₃ transparent ceramics in contrast to single La³⁺ and single Zr⁴⁺ doped Tm:Y₂O₃. Samples with composite sintering aids could realize fine microstructures and good optical properties at relatively low sintering temperatures. Grain sizes around 10 μm and transmittances close to theoretical value at wavelength of 2 μm were achieved for the 9 at.% La³⁺, 3 at.% Zr⁴⁺ co-doped samples sintered at 1500-1600 °C. The influences of the composite sintering aids on the emission intensities and the phonon energies of Tm:Y₂O₃ ceramics were also investigated.     

Structural-phase state and lasing of 5–15 at% Yb3+:Y3Al5O12 optical ceramics

Yttrium aluminum garnet (Yb³⁺:Y₃Al₅O₁₂) laser ceramics doped by 5, 10 and 15 at% of ytterbium ions were obtained by reactive sintering. Optimal sintering temperature range for the formation of highly-dense transparent Yb³⁺:Y₃Al₅O₁₂ ceramics under normal recrystallization conditions was found to be T = 1750–1800 °C. The influence of Yb³⁺ ions on structural-phase state, phase composition, microstructure, optical and luminescent properties of sintered samples was experimentally investigated. It was shown that lattice parameter a of Yb³⁺:Y₃Al₅O₁₂ ceramics decreases linearly with increasing of Yb³⁺ concentration in a good agreement with L. Vegard’s rule, that indicates to the formation of (Y_1−xYb_x)₃Al₅O₁₂ (х = 0.05–0.15) substitutional solid solutions. No concentration quenching of Yb³⁺ luminescence was observed in Yb³⁺:Y₃Al₅O₁₂ within the 5–15 at% doping range. Quasi-CW lasing of Yb³⁺:Y₃Al₅O₁₂ ceramics was studied under diode-pumping at 970 nm. A highest slope efficiency of about 50% was obtained for 15 at%-doped Yb³⁺:Y₃Al₅O₁₂ ceramics sintered at T = 1800 °C for 10 h.     

Study on the effect and mechanism of zirconia on the sinterability of yttria transparent ceramic

Transparent Y₂O₃ ceramics were fabricated by solid-state reaction using high purity Y₂O₃ and ZrO₂ powder as starting material. The results indicated that ZrO₂ additive can improve the transparency of Y₂O₃ ceramic greatly. The best transmittance appears with 3 at.% ZrO₂ doped Y₂O₃ transparent ceramic with transmittance at 1100 nm of 83.1%, which is up to 98.6% of the theoretical value. The microstructure is uniform and no secondary phase is observed in the ceramic with the average grain size of 15 μm. The mechanism of ZrO₂ improving the transparency of Y₂O₃ ceramic is analyzed in detail. On this basis, Yb³⁺ doped Y₂O₃ transparent ceramic was also fabricated and spectroscopic properties were investigated.     

MgO-Y2O3:Eu composite ceramics with high quantum yield and excellent thermal performance

MgO-Y₂O₃:Eu composite ceramics with high quantum yield and excellent thermal performance were successfully synthesized by vacuum sintering. All samples exhibited uniform composite microstructures and pure binary phase. Eu³⁺ ions were completely incorporated into Y₂O₃ phase, and the optimal Eu concentration is 15 at%. Sintered at 1800 °C, the fluorescent properties of MgO- z vol% Y₂O₃: Eu (z = 30, 40, 50, 60, 70, 100) composites proved to be independent on component proportion, including the similar fluorescence lifetimes (953–983 μs), quantum yield (70%−80%), and activation energy (ΔE) of thermal quenching (0.163 eV). Significantly, thermal conductivity of composites with 30 vol%, 50 vol% and 70 vol% MgO attained 11.58, 17.45, and 29.65 W/(m∙K) at room temperature, which are nearly 2, 3, and 5 times as high as that of 15 at% Eu:Y₂O₃ ceramic (5.90 W/(m∙K)), respectively, demonstrating their potential for application in high-power-density display and lighting technology.     

Plasma etching properties of various transparent ceramics

The etching properties of four types of transparent ceramics: sapphire (a single crystalline α-Al₂O₃), γ-AlON (γ-aluminum oxynitride), Mg-spinel (MgAl₂O₄), and Y₂O₃, as well as a polycrystalline opaque Al₂O₃ were examined using an inductively coupled plasma etcher under an incident plasma power of 2,000 W for up to 3 h. The transparent γ-AlON and opaque Al₂O₃ showed significant surface morphological changes, whereas sapphire, Mg-spinel, and Y₂O₃ revealed a relatively smooth surface upon etching. However, direct correlation between the surface morphological change and the degree of etching could not be drawn because sapphire showed a uniform surface etching despite its significant mass loss. Even though Y₂O₃ was found to be more plasma-resistant than Al₂O₃, overall, Mg-spinel was the most feasible transparent material for monitoring window application in a semiconductor processing chamber because of its minimal degree of erosion (≤0.4g/m²) and the transmittance change (≤2%) upon 3 h of fluorocarbon (CF₄) plasma etching.     

Effects of Ho3+ concentration on the fabrication and properties of Ho: Y2O3-MgO nanocomposite for Mid-infrared laser applications

Infrared transparent Ho: Y₂O₃-MgO nanocomposite ceramics with a volume ratio of 50:50 (RE₂O₃: MgO) were prepared by combining sol-gel powder synthesis and hot-pressing sintering techniques. In order to obtain Ho: Y₂O₃-MgO nanocomposite ceramics with fine grain size, dense microstructure and homogeneous phase domains, the effect of sintering temperature and Ho³⁺ doping concentration were studied. Transmittance and SEM measurement revealed that the grain size of 3 at.% Ho: Y₂O₃-MgO ceramic sintered at 1250 °C is 141 nm, and the transmission is up to 85.2% at 5 μm. The detailed spectroscopic investigation of x at.% Ho: Y₂O₃-MgO (x = 1, 3, 5, 7, 9, 15) ceramics was performed. The nanocomposites exhibited photoluminescence properties similar to that of Ho: Y₂O₃ crystals and ceramics. In addition, the thermal conductivity of 3 at.% Ho: Y₂O₃-MgO ceramic is 13.04 W/m·K, which is superior to that of Ho:Y₂O₃ ceramics. The high transmission, excellent thermal conductivity, and outstanding optical characteristics indicated that Ho: Y₂O₃-MgO ceramics is a promising material for efficient infrared solid-state laser.     

Effect of air annealing on the optical properties and luminescence performance of Ce:YAG ceramics for light-emitting diodes at different Ce concentrations

(Y_1-x%Ce_x%)₃Al₅O₁₂ (x = 0.2,0.4,0.6,0.8,1.0) transparent ceramics were fabricated by vacuum sintering technology, followed by air annealing at different temperatures. Transmittance of ceramics, valence of cerium, and luminescent properties with varying annealing temperatures are studied in detail. The negative effect of Ce³⁺ oxidation induced by annealing gets increasingly evident when Ce concentration increases. Collaborating Ce:YAG ceramics with InGaN blue chips, light-emitting diodes (LEDs) with superior performance were constructed. The relationships between Ce concentration, annealing temperature, and luminous flux of LEDs are elucidated, showing that the optimized annealing temperature of Ce:YAG ceramics decreases from 1200 °C to 900 °C as Ce concentration increases from 0.2 at% to 1.0 at%. The luminous fluxes of optimized LEDs increase by ～10 % compared with that of unannealed LEDs.     

Highly transparent polycrystalline Gd2O3 ceramic attained via ZrO2 stabilization effect

The transition from the cubic to monoclinic phase of Gd₂O₃ at high temperatures poses a significant challenge to the preparation of transparent Gd₂O₃ materials. In this work, we presented a straightforward yet effective method for fabricating transparent Gd₂O₃ ceramics. Via ZrO₂ stabilization effect for phase structure, highly transparent Gd₂O₃ ceramics were successfully fabricated by vacuum sintering at 1850 °C for 8 h. The effect of different Zr (0 ∼ 13 at%) concentrations on phase transition, grain growth, fracture mode and optical properties of Gd₂O₃ transparent ceramics was investigated. As the Zr content increases, the transition from the cubic (C) to monoclinic (M) phase is effectively suppressed, which is crucial for achieving Gd₂O₃ transparent ceramics. Moreover, the results indicate that the addition of ZrO₂ has a significant effect on grain growth by not only impeding the migration of grain boundaries but also affecting the phase composition. In addition, the 11 at% Zr-doped Gd₂O₃ ceramic exhibits the best optical properties, of which transmittance is about 76% at 850 nm and about 80% in the 2.5 µm ∼ 6 µm mid-infrared range. This work provides an illustrative example for the development of other ceramics with phase transition. The obtained Zr-doped Gd₂O₃ transparent ceramics with high optical quality are potential candidates for optical window, scintillator host and mid-infrared transmission materials.