Table of Content

15 November 2024, Volume 53 Issue 11

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Research Progress on High-Melting-Point Rare Earth Oxides Laser Crystals

REN Yongchun, LI Jianda, CAO Xiao, HUANG Yi, ZHANG Fan, ZHANG Ning, XUE Yanyan, WANG Qingguo, TANG Huili, XU Xiaodong, DONG Yongjun, XU Jun

2024, 53(11):  1829-1839. 

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High-melting-point rare earth oxides, due to their advantages of high thermal conductivity, high mechanical strength, low phonon energy, and high cation site density, exhibit characteristics such as large segregation coefficients, strong electron-phonon coupling, and multiple lattice sites. These properties have made them a hot topic of research in high-power, ultrafast, and infrared laser crystals. However, their high-melting-points, particularly for sesquioxides (~2 450 ℃), pose significant challenges for crystal growth. Though being reported decades ago, the development of sesquioxide crystals remains in its early stage. In recent years, breakthroughs in various crystal growth techniques have been achieved, leading to a diversification of rare earth ion-doped laser research. This paper reviews the advantages of high-melting-point rare earth oxides, recent advancements in crystal growth, and the progress in laser performance across the infrared 1, 2 and 3 μm wavelength bands.

Research Progress of 3D Printing Yttrium Aluminum Garnet-Based Laser Ceramics

JI Haohao, CHEN Nianjiang, ZHANG Jian, YANG Yuhan, LIU Yu, WANG Shiwei

2024, 53(11):  1840-1867. 

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The development direction of advanced solid-state lasers is higher output power and better beam quality. Rare earth ion doped yttrium aluminum garnet transparent ceramics are preferred materials for solid-state laser gain media, but thermal effects during the pumping process deteriorate the beam quality and hinder further increase in output power. The heat generation and dissipation of laser ceramics with complex configurations are more uniform during the pumping process, which can significantly reduce thermal effects. Compared with traditional preparation methods, 3D printing is able to form more complex design structures, suppress thermal effects, and achieve integration and miniaturisation of multi-module devices, driving lasers towards a wider range of applications. In this paper, several traditional methods for the preparation of laser ceramics with complex configurations are introduced firstly, and the advantages and limitations are analyzed. Then, the research status and problems in 3D printing yttrium aluminum garnet-based laser ceramics are systematically reviewed. Common 3D printing methods include direct ink writing, stereolithography, digital light processing, material jet printing, two-photon polymerization and micro-continuous liquid interface printing. Among them, there are interlayer defects in the samples printed by stereolithography and digital light processing, resulting in severe scattering losses. Material jetting printing combined with dry pressing can be used to manufacture planar waveguides. Two-photon polymerization and micro-continuous liquid interface printing are suitable for the fabrication of highly complex structures at micrometer scales. Direct ink writing not only enables the fabrication of laser ceramics for the first time, but also has the most extensive relevant research and is still the most promising method for the preparation of laser ceramics with complex configuration. At the end of this paper, the current problems and research prospects of yttrium aluminum garnet-based laser ceramics prepared by 3D printing are summarized.

Spectral and Laser Properties of Er³⁺-Doped CaYAlO₄ Crystals

ZHANG Zhiheng, HOU Wentao, LIU Jian, LI Dongzhen, XUE Yanyan, WANG Qingguo, LYU Shasha, XU Xiaodong, XU Jun

2024, 53(11):  1868-1876. 

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Er³⁺-doped CaYAlO₄ crystals with the doping concentration (atomic fraction) of 15% and 30% were successfully grown by Czochralski method. The polarized spectral and laser properties of Er∶CaYAlO₄ crystals were studied. The polarized absorption spectra, polarized emission spectra and fluorescence decay curves were measured at room temperature. The disorder of CaYAlO₄ crystal results in broadband characteristics of absorption and emission spectra. The emission cross section of 15% Er∶CaYAlO₄ is determined to be 1.22×10^-20 cm² at 2 712 nm for σ polarization and 0.71×10^-20 cm² at 2 754 nm for π polarization, with a full width at half maximum (FWHM) of 152 and 167 nm, respectively. As Er³⁺ concentration increases, fluorescence lifetime of ⁴I_11/2 and ⁴I_13/2 energy levels decreases in different degrees, and lifetime ratio (τ_lower/τ_upper) greatly reduces. The energy transfer upconversion ETU1 not only suppresses self-termination effect but also improves quantum efficiency of 2.7 μm radiative transition. Under 974 nm LD excitation, laser property for output couple mirror with a transmittance of 1.5% is best. The maximum output power is 358 mW at 2 720 nm with a slope efficiency of 15.4% in c-cut 15%Er∶CaYAlO₄ crystal.

Growth, Spectroscopic Properties and Laser Performance of Nd∶ASL Single Crystal Fibers

GUO Jun, LIU Jian, WANG Zebin, CHEN Peng, SONG Qingsong, MA Jie, WANG Qingguo, XU Xiaodong, XU Jun

2024, 53(11):  1877-1883. 

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Nd³⁺-doped Sr_0.7La_0.3Mg_0.3Al_11.7O₁₉ (Nd∶ASL) single crystal fibers with different Nd³⁺ concentration were successfully grown by the micro-pulling-down (μ-PD) method. The crystal structure, polarized spectroscopic properties and continuous wave laser performance were studied. The Judd-Ofelt parameters Ω₂, Ω₄ and Ω₆ are obtained to be 1.093×10^-20, 2.285×10^-20 and 2.117×10^-20 cm², respectively. The fluorescence lifetime of 0.5%, 1.0%, 3.0% and 5.0%Nd∶ASL single crystal fibers are 375,398,384 and 363 μs, respectively. A continuous wave laser is obtained by pumping with a commercial laser diode of 800 nm emission wavelength. The maximum output power is 1.08 W at 1 055 nm with a slope efficiency of 18.5%. All the results indicate that Nd³⁺-doped ASL single crystal fiber grown by the μ-PD method has potential as a laser gain medium for laser system.

Fabrication and Laser Performance of Yb∶Lu₂O₃ Transparent Ceramics

LI Qing, JIANG Zhenxing, WANG Ying, MA Jie, WANG Jun, LIU Peng, ZHANG Jian, FAN Jintai, YU Haohai, ZHANG Huaijin, TANG Dingyuan

2024, 53(11):  1884-1891. 

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Rare-earth ions doped sesquioxide ceramics exhibit notable advantages, including high thermal conductivity, low phonon energy, and high laser damage threshold, thereby demonstrating significant potential for solid-state laser applications. Powders with high purity and low agglomeration were synthesized by chemical co-precipitation method, then 5% (atomic fraction) Yb∶Lu₂O₃ transparent ceramics with high density and high transparency were obtained through oxygen pre-sintering and hot isostatic pressing (HIP) sintering. The samples have an average grain size of less than 1 μm, and exhibit an in-line transmittance of above 81% at 1 100 nm. The absorption cross-section at 974 nm is ~0.97×10^-20 cm², and the emission cross-section at 1.08 μm is ~0.39×10^-20 cm². Using a 976 nm laser diode as the pump source, a continuous-wave (CW) laser output at 1 080.1 nm is achieved from the fabricated Yb∶Lu₂O₃ ceramics at room temperature, with a output power of 11.67 W and slope efficiency of 55.3%.

Fabrication and Properties of Er∶Lu₂O₃ Transparent Ceramics with Different Doping Concentrations

LIU Ziyu, ZHENG Wenwen, FENG Yagang, YE Junhao, LIU Peng, YANG Xianfeng, LI Jiang

2024, 53(11):  1892-1900. 

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Er∶Lu₂O₃ transparent ceramics are one of the candidate solid-state gain media for high efficiency and high power laser in the near and mid-infrared bands due to the advantages of high thermal conductivity, high thermal shock resistance, good spectral properties and low preparation temperature. Exploring the influence of Er³⁺ doping concentration (atomic number fraction) on the preparation and properties of Er∶Lu₂O₃ transparent ceramics for the related laser application is crucial for achieving high-quality Er∶Lu₂O₃ ceramics. In this paper, Er∶Lu₂O₃ transparent ceramics were fabricated using vacuum pre-sintering combined with hot isostatic pressing (HIP) post-treatment from the nano-powders synthesized by the coprecipitation method. The results show that the phases of all Er∶Lu₂O₃ nano-powders calcined at 1 100 ℃ with different Er³⁺ concentrations are almost consistent with that of the pure cubic Lu₂O₃ and the 10%Er∶Lu₂O₃ nano-powder shows better dispersibility. The average grain sizes of 0.3% and 10%Er∶Lu₂O₃ ceramics pre-sintered at 1 500 ℃ are 0.86 and 0.87 μm with the relative densities of 95.1% and 96.2%, respectively. The corresponding pre-sintered ceramics were HIP-ed at 1 750 ℃ show the in-line transmittance of 71.6% and 78.0% (thickness 2.9 mm) at 2 400 nm, respectively. Especially, the in-line transmittance of the 0.3%Er∶Lu₂O₃ ceramics sharply decreases in the short wave range due to the numerous remained residual pores. The absorption and emission spectra of 0.3% and 10%Er∶Lu₂O₃ transparent ceramics were calculated. 0.3%Er∶Lu₂O₃ ceramics possesses higher absorption and emission cross-sections around the band centered at 1.55 μm.

Fabrication and Properties of Layer-Structured YAG/Yb∶YAG Transparent Ceramics

FENG Yagang, TIAN Feng, LIU Ziyu, LIU Yiyang, WU Lexiang, LI Tingsong, LI Jiang

2024, 53(11):  1901-1908. 

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Using high-purity commercial oxide powders as raw materials, the layered composite ceramic green bodies that meet the design requirements were obtained by dry pressing combined with cold isostatic pressing. Two-layered and three-layered composite YAG/10%Yb∶YAG (atomic number fraction) transparent ceramics with high optical quality were successfully fabricated by vacuum pre-sintering at 1 750 ℃ for 30 h combined with hot isostatic pressing at 1 750 ℃ for 3 h under 200 MPa Ar. The optical transparency, microstructure and elemental distribution of the composite ceramics were analyzed. The results show that, the in-line transmittance values of two-layered and three-layered composite YAG/Yb∶YAG transparent ceramics with the thickness of 4 mm are 83.6% and 84.1% at 1 100 nm, respectively. Both YAG and Yb∶YAG ceramic regions have dense microstructure, and the average grain sizes are 29.0 and 34.5 μm, respectively. The element analysis of surface scanning images and linear scan images for the central section reveal that the boundary between YAG and Yb∶YAG ceramic region is straight, with Yb element mainly existing in the Yb∶YAG ceramic region, indicating that the actual structure of the layer-structured transparent ceramics is consistent with the initial design.

Valence Regulation and Optical Properties of Cr-Doped YAG Transparent Ceramics

HUANG Qiufeng, DENG Zhiqiang, CHEN Jian, GUO Wang, DENG Zhonghua, LIU Zhuguang, HUANG Jiquan

2024, 53(11):  1909-1917. 

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Cr⁴⁺∶YAG crystal materials have been proved to be an ideal passive Q-switched material in recent years. Using MgO and CaO as sintering aid and charge compensation agent, 0.25%Cr⁴⁺∶YAG (molar concentration) transparent ceramics with high optical quality were successfully prepared by low-temperature vacuum sintering combined with hot isostatic pressing (HIP) sintering. Effect of MgO, CaO, and MgO-CaO co-added divalent oxides on the transmittance, absorption spectra, and fluorescent properties of Cr⁴⁺∶YAG ceramics were investigated. It is found that, compared with CaO and MgO-CaO series, MgO exhibits the most significant effect on the densification of Cr⁴⁺∶YAG ceramics when the vacuum-sintering temperature is 1 550 ℃. Especially when the molar concentration of MgO is 0.25%, the relative density reaches 98%. After HIP sintering at 1 680 ℃, the corresponding in-line transmittance of the densified Cr⁴⁺∶YAG ceramics reaches as high as 84.4% at the wavelength of 1 400 nm. Moreover, by annealing at 1 400 ℃ for 20 h, the absorption coefficient of Cr⁴⁺ at 1 030 nm reaches the highest value of 3.0 cm^-1, though some Cr³⁺ still remain in the Cr⁴⁺∶YAG ceramics.

Pressure-Assisted Sintering and Properties of Yb∶CaF₂ Transparent Ceramics

LIU Qiang, LI Xiang, GUO Lihao, TOCI Guido, PIRRI Angela, PATRIZI Barbara, VANNINI Matteo, WU Junlin, LI Jiang

2024, 53(11):  1918-1926. 

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The 5%(atomic fraction) Yb∶CaF₂ nano-powders were synthesized by chemical co-precipitation method. Following freeze-drying, the agglomeration degree of the powders reduces, and the powders exhibit cubic lamellar structures with an average particle size of approximately 40 nm. High optical quality 5%Yb∶CaF₂ transparent ceramics were subsequently fabricated through hot pressing, supplemented by hot isostatic pressing (HIP) sintering as a post-treatment, utilizing the freeze-dried powders. The densification behaviour of the samples during the hot pressing process was investigated. The microstructure, in-line transmittance, absorption spectra, and laser performance of the ceramics were assessed and analyzed. The findings indicate that activation threshold of densification driving force occurs during the holding stage of the hot pressing process, and the HIP post-treatment effectively compresses and removes residual pores within the hot pressed ceramics, thereby significantly enhancing their optical quality. The in-line transmittance of the 5%Yb∶CaF₂ transparent ceramics, produced through hot pressing (625 ℃×2 h, 50 MPa) followed by HIP post-treatment (600 ℃×3 h, 100 MPa Ar), is 72.6% and 92.2% at 400 and 1 200 nm, respectively, with a thickness of 2 mm. Additionally, the absorption cross-section at 976 nm is determined to be 0.52 ×10^-20 cm². A fiber-coupled diode laser (LD) with a wavelength of 930 nm served as the pumping source for end-face pumping of the Yb∶CaF₂ transparent ceramics, obtaining a quasi-continuous laser output with a peak power of 0.81 W and a slope efficiency of 9.7%.

Research Progress on Vacuum Solid-State Reaction Preparation and Lattice Substitution of TAG Magneto-Optic Ceramics

CHEN Jie, SHEN Shiji, TIAN Yanna, ZHOU Shengming

2024, 53(11):  1927-1935. 

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As a typical garnet transparent ceramic used in high-energy solid-state laser systems, terbium aluminum garnet (Tb₃Al₅O₁₂, TAG) magneto-optic ceramics have become a focal point of research due to their excellent magneto-optic properties and high-power performance. This paper focuses on TAG magneto-optic ceramics prepared by vacuum solid-state reaction, with particular emphasis on the optimization of sintering aids and lattice doping modifications. By comparison, the most suitable additives for TAG ceramics were identified. The study highlights the longstanding challenge in improving the quality of TAG ceramics, which arises from the reliance on large doses of sintering aids and the resulting compositional inhomogeneity caused by sintering aid residues. To address these issues, we present our latest research, which involves co-doping the lattice with Mg²⁺ and Si⁴⁺. This approach enables the preparation of higher optical quality TAG ceramics via a one-step vacuum solid-state sintering process, without reducing the absolute amount of MgO and TEOS. The best sample achieve a transmittance of 82.48% at 1 064 nm, which, to our knowledge, is the highest value reported using a similar sintering method based on domestic powders. This lattice doping strategy, rather than the traditional mass-ratio addition of sintering aids, offers a promising new approach for further improving the quality of garnet transparent ceramics used in high-energy laser systems.

Growth and Properties of Nd∶TSAG Crystal

DOU Renqin, HUANG Lei, WANG Xiaofei, GAO Jinyun, LIU Wenpeng, LUO Jianqiao, ZHANG Qingli

2024, 53(11):  1936-1943. 

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Nd∶TSAG magneto-optical crystal with the size of ϕ50 mm×100 mm were grown by Czochralski method for the first time. The structure, spectra, magneto-optical, and thermal properties of the crystal were studied in detail. Spectral parameters, such as oscillator strength, line strength, intensity parameter Ω_t, transition probability between ⁴F_3/2→⁴I_J energy levels, radiation lifetime, and fluorescence branching ratio were calculated. The doping concentration of Nd∶TSAG polycrystalline samples was optimized, and the best doping concentration of Nd³⁺(atomic fraction) is 1%. The results of X-ray diffraction analysis of crystal and powder show that the crystal has a pure phase and good crystal quality. The separation coefficient of Nd³⁺ in TSAG crystal is 0.64. In the visible and near infrared bands, the transmittance of Nd∶TSAG crystals is over 80%, except for the characteristic absorption of Tb³⁺and Nd³⁺. With 808 nm excitation, the strongest fluorescence peak of Nd∶TSAG is around 1 070 nm. The refractive indices of Nd∶TSAG crystals at 473, 532, 632.8, and 1 064 nm are 1.925 9, 1.915 3, 1.903 8, and 1.885 2, respectively. The four-parameter Sellmeier refractive index equation is fitted. The Verdet constants of Nd∶TSAG measured by extinction method at 405, 532, 635, and 1 064 nm are 599.8, 202.8, 152.3, and 46.8 rad·m^-1·T^-1, respectively, which are higher than that of TGG crystals. At room temperature, the thermal conductivity of Nd∶TSAG crystals is 3.95 W/(m·K). The results show that Nd∶TSAG is an excellent magneto-optical crystal and a potential excellent laser crystal. Meanwhile, it is promising to realize the synergistic effect of magneto-optic and laser.

Preparation and Properties of Rare Earth Ion Over-Doped TSAG and YAG/TSAG Composite Structural Transparent Ceramics

FENG Guiqing, XU Liuwei, YUAN Yazhou, ZHENG Yi, HUANG Xin, CHEN Min, WANG Shuaihua, WU Shaofan

2024, 53(11):  1944-1955. 

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In this paper, the effects of over-doping of Nd³⁺, Ho³⁺, Dy³⁺ and Ce³⁺ rare earth ions on the preparation and related properties of TSAG ceramics were investigated, and the results show that over-doping of rare earth ions has a certain effect on the micro-defects and transmittance of TSAG ceramics. The existence of a small number of fine particles which are not in the secondary phase on the grain surface, led to the decrease of the transmittance of the ceramic samples. The Verdet constant of rare earth ion over-doped TSAG ceramics is better than that of pure phase TSAG ceramics at the same test wavelength. In addition, YAG/TSAG-based bilayer composite structural ceramics were explored. The YAG/TSAG and YAG/2.0%Ce∶TSAG bilayer composite structural ceramics were successfully prepared, with sub-micron thickness transition layer formed on the contact surface, and the transmittance of the YAG/TSAG ceramics at 1 064 nm reaches 71.0%. The successful preparation of YAG/TSAG-based composite ceramics broadens the application prospects of TSAG materials in high-power lasers.

Electro-Optical Properties of PLZT Transparent Ceramics with Composition Regulating in Micro-Regions and Gradient Designing

WU Wenjie, HE Daihua, CHENG Siyuan, HE Xiyun

2024, 53(11):  1956-1963. 

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Lanthanide-doped lead zirconate titanate (PLZT) transparent ceramics have significant potential for application in modern optical communication and high energy laser technology due to their exceptional optical transparency and electro-optical effects. However, the electro-optical (E-O) properties of PLZT transparent ceramics are highly sensitive to changes of ambient temperature, which presents a significant challenge in their application in E-O modulators across a wide temperature range. The objective of this study was to investigate the effects of temperature on the ferroelectric, dielectric and E-O properties of PLZT (10/65/35) transparent ceramics, and optimize the material E-O properties and their temperature stability by regulating the distribution of the key doping element La³⁺ in micro regions. A series of PLZT ceramic samples with pure perovskite structures were obtained by a conventional hot-press sintering process in oxygen atmosphere. The resulting microstructures are uniform and dense, and the optical transmittances of the samples are 52%~60% at a wavelength of 632.8 nm. The broadened dielectric peaks of PLZT ceramics indicate the relaxation characteristics of the materials, and it is promoted as La³⁺ content increasing, and enhance obviously by the enlarged La³⁺ fluctuation in micro-regions in the 0-3 and 2-2 composite PLZT ceramics with a more broadened dielectric peak and higher dielectric constant. The ferroelectric hysteresis loops (P-E) of the PLZT ceramics all exhibit a gradual decrease in maximum polarization value (P_max), residual polarization value (P_r), and coercivity field strength (E_c) with the temperature increasing. P_max values of 0-3 and 2-2 composite PLZT (10/65/35) ceramics are obviously higher than that of the well-distributed PLZT (10/65/35) ceramics, and their equivalent secondary E-O coefficients are significantly increased near the temperature of diffuse phase transition.

Preparation and Opto-Electric Properties of Lead-Free 0.96KNNTS_x-0.04BNKZ Transparent Piezoelectric Ceramics

WANG Yaqi, FU Dashi, WANG Yanan, QIN Yalin, ZHANG Yongcheng

2024, 53(11):  1964-1971. 

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In this study, 0.96(K_0.48Na_0.52)(Nb_0.95-xTa_0.05Sb_x)O₃-0.04Bi_0.5(Na_0.82K_0.18)_0.5ZrO₃ (0.96KNNTS_x-0.04BNKZ, x=0.03, 0.04, 0.06, 0.07) lead-free transparent piezoelectric ceramics were prepared, and the effects of Sb doping levels on their piezoelectric properties and optical transparency were examined. All samples exhibit a perovskite structure. With increasing Sb content, both piezoelectric performance and transparency improve. Notably, at x=0.04, the piezoelectric coefficient reaches 240 pC/N, with an optical transmittance of 31.5% at 780 nm. This study demonstrates that compositional design can achieve enhanced transparency and high piezoelectric performance in KNN-based lead-free ceramics, offering significant potential for applications in optoacoustic imaging and transparent transducers.

Kinetic Study on the Sintering Process of Zn_1.1Ga_1.8Ge_0.1O₄ Transparent Ceramics

WANG Kaiqiang, YANG Kang, JING Zhengyang, CHEN Bowen, TU Bingtian, WANG Hao

2024, 53(11):  1972-1980. 

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Spinel-type Zn_1.1Ga_1.8Ge_0.1O₄ is an excellent host material for dielectric and long-persistent luminescent ceramics. It is helpful to expand application when the transparent ceramics is fabricated. In this paper, the pressureless sintering kinetics of Zn_1.1Ga_1.8Ge_0.1O₄ ceramics were studied. The results show that both densification and grain growth are controlled by the grain boundary diffusion of O^2-. The activation energy for densification in the intermediate sintering stage is determined as (426±35) kJ/mol, while the activation energy for grain growth in the final sintering stage is calculated as (439±14) kJ/mol. When the combination of sintering parameters is optimized to enter into the so-called “sintering window”, the favorable microstructure of the pressureless-sintered body is obtained. After hot isostatic pressed at high temperature, Zn_1.1Ga_1.8Ge_0.1O₄ transparent ceramics with optical transmission ranging from 0.3 μm to 9 μm and in-line transmittance of 81.2% at 2.5 μm are prepared.

Preparation of Y₂O₃ Transparent Ceramics by Colloidal Forming Method Based on the Synergistic Effect of Double Dispersants

QU Shengxiao, MU Haojie, YANG Liang, LI Xiaodong, SHI Shujun, SUN Xudong

2024, 53(11):  1981-1989. 

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The preparation of a well-dispersed, high solids content suspension is the foundation for colloidal forming methods to achieve ceramic green bodies with a uniformly microstructure, and meet the application requirements of various optical window materials. This article aims to enhance the dispersion stability of Y₂O₃ suspension by utilizing the synergistic effect of two dispersants, namely triammonium citrate (TAC) and ammonium polyacrylate (A40). The influence of the mixing ratio of two dispersants on the stability of Y₂O₃ suspension and the microstructure of formed green bodies were mainly investigated, and the advantages of the dual dispersant system in improving the solid content and stability of Y₂O₃ suspension were determined. The results show that the solid content of Y₂O₃ suspension could reach 38% (volume fraction) under the condition of TAC to A40 mass ratio of 7∶3. A uniformly microstructure and densely packed particle was achieved. Y₂O₃ transparent ceramics with a diameter of 9 mm and a thickness of 1 mm were obtained by vacuum sintering at 1 800 ℃, with a transmittance of 70.34% at 800 nm.

Influence of Acid-Washing Treatment of Y₂O₃ Nanopowder on the Optical Properties of Transparent Ceramics

LIU Xiaolong, FU Zhongchao, WU Nan, LONG Haibo, SHAO Cen, REN Yi, HOU Zhaoxia, ZHANG Le

2024, 53(11):  1990-1996. 

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Y₂O₃ transparent ceramics have broad applications including solid-state lasers, transparent windows, etc., owing to its excellent optical and physical-chemical properties. The dispersity of the powder among the fabrication process of transparent ceramics has attracted much attention from researchers for decades. In this paper, domestic commercial nanopowder was adopted as the starting material, and the dispersion of the powder was improved through mechanical force combined with HF acid-washing. Y₂O₃ transparent ceramics with high transmittance were achieved by slip casting and vacuum sintering. The results show that ultrasonic combined with HF acid-washing is an effective way to improve the dispersibility and sinterability of the powder, the D₅₀ of the powder reduces from 3.5 μm to 1.4 μm. The transmittance of the Y₂O₃ ceramic at 400 nm is improved from 65.5% to 71.5% for the sample after ultrasonic combined with HF acid-washing process. The results lay a solid foundation of preparation technology and theoretical basis for the application of Y₂O₃ transparent ceramics on solid-state lasers and transparent window materials.

Fabrication and Microstructure of Y³⁺∶CaF₂ Transparent Ceramics

LIU Zuodong, PAN Qiyue, LIU Rui, CAO Yue, LI Siya, WANG Jiashun, YU Yongsheng, LIU Peng, JING Qiangshan

2024, 53(11):  1997-2003. 

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Y³⁺∶CaF₂ powders were synthesized by chemical coprecipitation method, and transparent ceramics were fabricated by vacuum hot pressing sintering method. Characteristics of the as-synthesized powders were investigated by XRD, SEM and TEM techniques, the relationship between microstructure and transmittance of transparent ceramics were also analyzed. Crystal structures of as-synthesized Y³⁺∶CaF₂ powders belong to single fluorite phase. With the Y³⁺ doping content increases, the average particles sizes decrease and the lattice constants increase from 5.452 1 Å to 5.465 5 Å. The 5%Y³⁺∶CaF₂ transparent ceramics sintered at 900 ℃ for 3 h exhibits the highest transmittance, and the transmittance at 500 and 1 500 nm are 73.1% and 86.4%, respectively. Microstructure of ceramics are modified by the Y³⁺ doping content and sintering temperatures. For a low growth velocity, it is not easy to eliminate the residual pores, while for a higher growth velocity, residual pores are easily embedded within grains. Both cases will reduce the transmittance of transparent ceramics. This work provides a reference for the preparation of high-quality composite CaF₂ transparent ceramics.

Effects of Calcining Temperature in the Preparation of Y₂O₃ by Pechini Method on the Transparency of Pressureless Sintered AlON Ceramics

GUO Haoran, YAN Hui, SHAN Yingchun, GAO Mingze, XU Jiujun, LI Jiangtao

2024, 53(11):  2004-2012. 

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Using Y(NO₃)₃·6H₂O as yttrium source, nano-sized Y₂O₃ powder was obtained by calcining the precursor prepared by Pechini method. This Y₂O₃ powder was then used as a sintering additive to fabricate transparent AlON ceramics via pressureless sintering at 1 880 ℃ for 2.5 h. The effects of precursor calcination temperature on the composition, morphology and particle size of Y₂O₃ powder, as well as on the transparency of AlON ceramics were thoroughly studied. The results indicate that increasing calcination temperature of the precursor can promote the decomposition of organic compounds, but it also leads to the growth of Y₂O₃ particles. Residual organic compounds and excessive growth of Y₂O₃ powders are unfavorable for fabrication of AlON ceramics with high transmittance and high relative density. The nano-sized Y₂O₃ powder prepared by calcining the precursor at 900 ℃ for 2 h is favorable for the fabrication of highly transparent AlON ceramics via rapid pressureless sintering. The infrared transmittance of the obtained AlON ceramics reaches up to 83.4% at ~3 750 nm.

Absorption Coefficient of Magnesium Aluminate Spinel Transparent Ceramics

LEI Muyun, LI Zhen, WANG Ying, HE Jinghui, WANG Lidi, PANG Zhenli

2024, 53(11):  2013-2021. 

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With the increase of laser power, high-energy laser systems have increasingly demanding requirements for laser exit aperture windows. Magnesium aluminate spinel (MgAl₂O₄) transparent ceramics exhibit excellent optical, thermal, and mechanical properties, making them widely used in infrared guidance windows, high Mach aircraft radomes, and windows for optoelectronic equipment in extreme environments. However, there are relatively few reports on their use as laser exit aperture windows. This article briefly introduces the current state of research and development of magnesium aluminate spinel transparent ceramics for laser exit aperture window applications. Focusing on the most critical performance aspects for this application, the absorption coefficient of magnesium aluminate spinel transparent ceramics currently used in transparent bulletproof armor and aircraft windows are tested. The purity of magnesium aluminate spinel powders prepared by the bimetallic alcoholate method and the magnesium aluminate spinel transparent ceramics produced using hot pressing combined with hot isostatic pressing techniques are analyzed. Furthermore, the factors affecting the absorption coefficient of the ceramics are discussed.