Dy3+-doped Y2Zr2O7 highly transparent ceramics for ultraviolet excitable warm white light-emitting applications

Attaining effective warm white light emitting in functionally advantageous transparent polycrystalline ceramics is vitally important to guarantee the development of both human and botanical systems. In response to this aim, a series of Dy³⁺-doped Y₂Zr₂O₇ (YZO) transparent ceramics were prepared via a solid-state reaction and vacuum sintering approach in this work. These fabricated ceramics show high transparency, where the in-line transmittance at 700 nm is about 76%, which is very close to the theoretical limit (78%). In addition, under the excitation of UV light sources (358 and 384 nm), strong warm white light emissions were observed in these YZO:Dy transparent ceramics. The corresponding photoluminescence characteristics and mechanisms of YZO:Dy ceramics are investigated carefully. The Dy-doped YZO ceramics integrate with high transparency and UV-excitable warm white light emission properties, making them promising light-emitting converter materials for light-emitting source applications.     

Transparent ceramics for lighting

The development of ceramic arc lamps for optical applications requires consideration of materials other than sintered polycrystalline alumina (PCA). Regular PCA is translucent, not transparent. Except small-grained, regular PCA cannot be used for high luminance applications such as required by projection systems. Silica lamps are currently operating close to their limit in highly loaded discharge lamps. These may be replaced with ceramic lamps so the Hg pressure may be elevated and/or higher powers achieved. Cubic materials can be polished to transparency for use as optical sources of short arcs. The current paper surveys the composition, structure, and properties of transparent ceramic lamp tube materials including small-grained PCA, sapphire, aluminum oxynitride, yttrium aluminate garnet, and dysprosium oxide. The challenges beyond the optical transparency are to achieve (1) strong bonding between the transparent ceramic and electrode system to complete the discharge enclosure, (2) satisfactory characteristics including thermo-mechanical properties in order to withstand the rapid heating and cooling cycles encountered in both the discharge tube and seal, (3) durability to resist the attack from lamp chemicals at high temperatures, and (4) stability to maintain the optical quality throughout the life. Performance, energy efficiency, environmental sustainability, and economics are driving the development of ceramic envelopes in lighting products. Transparent ceramics offer opportunities to push the limits of envelope materials for improved lamps. The paradigm used during the course of transparent ceramics research exemplifies advancement of new and improved materials.     

Ho3+-doped (K,Na)NbO3-based multifunctional transparent ceramics with superior optical temperature sensing performance

Ho³⁺-doped (K_0.5Na_0.5)NbO₃-based transparent ceramics have been prepared via pressureless solid-state method. The ceramics possess moderate optical transparency with the energy band gap of ~2.9 eV and submicron-sized grains (<500 nm). The temperature-dependent dielectric properties and ferroelectric polarization-electric field hysteresis loops demonstrate that the ceramics own relaxor-like characteristics. The up-conversion photoluminescence and optical temperature sensing properties of the ceramics have been investigated. The temperature dependence of photoluminescence provides a fluorescent method to detect phase transitions, which can be expanded to other ferroelectric systems. The outstanding optical temperature sensitivity (~0.0075/K at 430 K) of the ceramic is higher than many other rare-earth-doped ceramics or glasses. These results suggest that the Ho³⁺-doped (K_0.5Na_0.5)NbO₃-based transparent ceramics are promising lead-free transparent materials for multifunctional applications, especially in temperature sensing devices.     

Modelling transparent ceramics to improve military armour

The dominant materials solution used for ballistic transparency protection of armoured tactical platforms in commercial and military applications is low cost glass backed by polycarbonate. Development of next generation ceramics is critical to offering enhanced protection capability and extended service performance for future armoured windows to the soldier. Due to the high cost of testing transparent ceramics, a modelling approach has been undertaken in parallel with ballistic testing to validate armour designs based on a transparent magnesium aluminate spinel, MgAl₂O₄, striking-ply backed by polycarbonate. A key purpose is to characterize the influence of defects on the failure of laminates, both statically and dynamically tested. Finite element modelling is used to predict unsuccessful designs and reduce number of laminate configurations in experimental testing. A notional ceramic armour system based on spinel/polycarbonate assemblies is used to report results on the effect of surface and interior, equal area defects on the ballistic behavior of a laminates.     

Influence of composition and microstructure on transparency and diffusivity in ion-exchangeable spinel glass-ceramics

Ion-exchangeable, transparent spinel glass-ceramics are presented and discussed here for the first time. To retain transparency with increasing crystallinity, spinel glass-ceramics must have uniform crystallization of small (~9 nm) crystallites, not large spherulitic structures comprised of small crystallites. To obtain such a uniform microstructure, the amount of total nucleating agents (ZrO₂ + TiO₂) in the precursor glass composition must be greater than 5 mol%. With small changes in composition and significant differences in microstructure, the demarcation between transparent and opaque glass-ceramics is distinct as is the decrease in K diffusivity during ion-exchange from the transparent (14.7 microns²/h) to the opaque (11.2 microns²/h) compositions. Understanding how to retain transparency during ceramming and increase diffusivity during chemical strengthening is critical in designing materials for many real-world applications. Ion-exchangeable, transparent spinel glass-ceramics are presented and discussed here for the first time. To retain transparency with increasing crystallinity, spinel glass-ceramics must have uniform crystallization of small (~9 nm) crystallites, not large spherulitic structures comprised of small crystallites. To obtain such a uniform microstructure, the amount of total nucleating agents (ZrO₂ + TiO₂) in the precursor glass composition must be greater than 5 mol%. With small changes in composition and significant differences in microstructure, the demarcation between transparent and opaque glass-ceramics is distinct as is the decrease in K diffusivity during ion-exchange from the transparent (14.7 microns²/h) to the opaque (11.2 microns²/h) compositions. Understanding how to retain transparency during ceramming and increase diffusivity during chemical strengthening is critical in designing materials for many real-world applications.     

IR transmission prediction,processing, and characterization of dense La2Ce2O7

High-throughput computation, based on density functional theory (HT-DFT), is used to predict the bounds for optical transparency, from the ultraviolet to the infrared, for materials in the pyrochlore family. The HT-DFT approach adopted here uses an initial screening from Materials-Project database, with millions of calculated properties. Band gaps and phonon spectra were calculated from selected pyrochlore crystal structures taken from the Materials Project database. Short and long wavelength bounds for optical transparency were calculated for chemistries with stable, cubic structures. The calculations predict that La₂Ce₂O₇ has one of the broadest range of transparency for the pyrochlore family. Based on these calculations, dense polycrystalline samples of La₂Ce₂O₇ were produced by sintering and hot-isostatic pressing. Transparency was characterized by methods that did not require large samples with high optical quality, obtaining 7.15 and 7.5 µm at 95% and 90% normalized transmittance, respectively. Bandgap calculations suggest a lower bound of UV transparency cut-off of 0.3 µm. The infrared wavelength cut-off is higher than that reported for other pyrochlores, and higher than for yttria, zirconia, or other common infrared transparent ceramics. We discuss our prediction and characterization methods as well as the suitability of pyrochlores for mid- and far-infrared optical applications.     

Fifty Years of Research and Development Coming to Fruition; Unraveling the Complex Interactions during Processing of Transparent Magnesium Aluminate (MgAl2O4) Spinel

The need for materials for demanding optical applications has engendered a resurgent interest in transparent ceramics. Transparent polycrystalline magnesium aluminate spinel is one especially promising and rapidly maturing technology that can fill this niche. Although it has been studied for over 50 yr, it is only recently that highly transparent components with acceptable mechanical properties have been reliably fabricated at reasonable cost. Development has been hindered by the inherent difficulty in sintering spinel to the near‐theoretical density required for transparency, a high sensitivity to powder and processing parameters, variable stoichiometry, and a lack of understanding of the synthesis–processing–property relationships. The driver of recent success is an emerging understanding of complex, multiscale, multivariable interactions that occur during green‐body formation and sintering. In particular, certain key variables play a decisive role in determining compact properties and their evolution must be controlled from synthesis to the finished product. This article features the interactions between these key variables during processing and gives an exposé of the state of the art in transparent polycrystalline spinel fabrication.     

Transparent AlON ceramic combined with VO2 thin film for infrared and terahertz smart window

Transparent AlON ceramics are intriguing window materials with excellent mechanical strength and superb optical transparency from the near ultraviolet to the mid-infrared range. However, previous studies focused their investigations in the visible range; therefore, the application of transparent AlON ceramics to tunable windows has yet to be reported. In this work, a VO₂ thin film with a characteristic semiconductor-metal phase transition (SMT) was fabricated on a transparent AlON ceramic, which exhibited remarkable tunable switching properties in the infrared and terahertz ranges. The transparent AlON ceramic was prepared by a two-step method, which included carbothermal reduction and pressureless sintering. The resulting ceramic exhibited high transparency of over 70% in the visible-infrared range and a notable THz transmission of 64.5–73.9% at 0.1–1.5?THz. The VO₂ thin film was prepared on a transparent AlON ceramic using the sol-gel method and showed excellent optical and electric switching performance. The square resistance variance was close to four orders of magnitude, and an infrared switching ratio of over 40% was obtained. Furthermore, the combined structure showed an efficient THz switching ratio of approximately 70.9%. This study proposes a composite material combined with a transparent ceramic and a phase transition oxide and provides great insights into their application in infrared and terahertz smart windows as well as in switching devices.     

Densification of 8Y‐Tetragonal‐Stabilized Zirconia Optoceramics with Improved Optical Properties by Y Segregation

8% Yttria‐stabilized zironcia (8YSZ) transparent ceramics have a wide technological applications. Segregation of the Y around the grain boundaries is favored by slow heating rate. The optimized sintering parameters helped in obtaining transparent ceramics of 8YSZ with a high percentage of cubic phase in addition to the presence of tetragonal phase. HRTEM was used to verify the grain growth suppression and to observe the presence of the cubic phase. The presence of cubic phase has suppressed the grain growth, which increased the transparency in the visible and infrared region without the addition of dopants or by utilizing high pressure.     

透明氧化铝陶瓷制备的研究进展

氧化铝陶瓷是第一个实现透明化的先进陶瓷材料,拓展了先进陶瓷材料的研究和应用领域;并作为高强度气体放电灯的关键部件一电弧管而获得实际应用.近半个世纪以来,人们在提高透过率的理论研究和优化制备工艺方面取得了众多成果.本文论述了影响透明氧化铝陶瓷透光性的各种因素,并且从氧化铝粉体、烧结助剂的选择及作用和烧结工艺等三方面综述了近年来国内外关于氧化铝陶瓷研究的工作与进展,对氧化铝透明陶瓷的制备进行了较为系统的综述,最后展望了透明氧化铝陶瓷的发展趋势.     

Effect of rare-earth oxide additives on transparency and fluorescence of α-SiAlON ceramics

Recently, novel transparent and fluorescent materials are in demand for various optical applications such as lasers, scintillators, and solid-state lighting. α-SiAlON, which has excellent thermal and mechanical properties, also exhibits photoluminescence depending on the stabilized doped rare-earth ions. Its transparency and fluorescence depend on the rare-earth oxide added as a raw material, particularly in conventional powder processing. In this study, we fabricated α-SiAlON ceramics by adding various rare-earth oxides to elucidate their effects on the transparency and fluorescence of these ceramics. High-transparency α-SiAlON ceramics were fabricated by adding rare-earth oxides whose rare-earth ions have small ionic radii: Y₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, and Lu₂O₃. Because the fraction of α-SiAlON was high, the relative density was high, and the microstructure was composed of fine grains. In particular, α-SiAlON ceramics prepared by adding Ho₂O₃ showed lower light scattering than the other fabricated α-SiAlON ceramics because of the smaller α-SiAlON grains, resulting in higher in-line transmittance (48% at 600 nm). Furthermore, these transparent α-SiAlON ceramics exhibited fluorescence corresponding to the activated rare-earth ions: Ho³⁺, Er³⁺, Tm³⁺, and Yb³⁺ or Yb²⁺.     

雷达波屏蔽隐身与光学透明兼容技术研究进展

雷达波测防与抗电磁干扰在军事和社会生活中需求迫切,基于透明应用的屏蔽隐身与光学透明兼容技术成为该需求牵引的重点研究方向之一。本文概述了近年来透明电磁波屏蔽隐身技术的研究现状,介绍了铟锡氧化物(ITO)及其复合材料、金属网栅、超材料、水基材料等新型透明吸波材料的结构,分析了材料的优势特点及不足,并对这几种材料在透明屏蔽隐身领域的未来发展进行了讨论和展望。     

Phase-separation engineering in fluorozirconate glass for designing and fabricating of transparent perfluorinate glass ceramic

Perfluorinate glass ceramics with ultra-low phonon energy are very important optical and photonic materials. Unfortunately, there is no suitable method to obtain transparent perfluorinate glass ceramics due to poor thermal stability of fluoride glass. As a result, wide applications of glass ceramics in advanced infrared systems are restricted. Here, an effective method based on phase-separation engineering is used to develop transparent perfluorinate glass ceramics. In this article, a novel transparent Er³⁺-doped ZnZrF₆-Ba₆Zn₇F₂₆ perfluorinate glass ceramic was designed and fabricated by phase-separation engineering. The sample exhibits low phonon energy (564 cm⁻¹), ultra-wide transmission range (0.33–8.2 μm, T ≥ 50 %), and strong infrared emission, which is better than that of ZBLAN glass, oxide-, and oxyfluoride-glass ceramics. These good properties of the perfluorinate glass ceramic demonstrate that phase-separation engineering not only offers an effective approach to obtain perfluorinate glass ceramics but also provides wide-ranging opportunities for advanced infrared optical and photonic materials.     

Phase composition,microstructure and luminescent property evolutions in “light-scattering enhanced” Al2O3-Y3Al5O12: Ce3+ ceramic phosphors

Classic transparent ceramics for laser gain medium and window materials may benefit from their distinctive features of structural homogeneity and high transparency at large scales. However, this has restricted the ability of the ceramics for local light management. Herein, a strategy for ceramic-phosphor design was conducted in the present work via introducing light-scattering centers into single phased YAG: Ce³⁺ transparent ceramics, and an enhancement of light extraction was experimentally realized through the control of Al₂O₃ grain size. UV–vis-NIR diffuse reflectance spectra further confirmed the important roles of the excrescent Al₂O₃ grains. More importantly, PL characterization shows orange-white light emission with high brightness at high temperature. The results highlight that the unique configuration enables simultaneous control of light propagation, luminous efficiency and thermal stability of luminescence, and the design strategy may create great opportunities for laser lighting and displays with high laser power density.     

Study on third-order optical nonlinear properties of transparent chalcogenide glass ceramics within Ge–S binary system

transparent chalcogenide glass ceramics (ChGCs) based on a binary germanium-sulfur (Ge–S, GS) chalcogenide system were synthesized by heat treatment method. Compared with the precursor glass, the GS ChGCs embedded with GeS₂ nanocrystals have the same infrared transparency, but smaller optical bandgap energy and higher mechanical strength. Z-scan measurements show that third-order optical nonlinearity in the GS ChGCs was remarkably enhanced, and this material would be suitable for applications in optical limiting.     

First ZnGa2O4 transparent ceramics

Transparent polycrystalline ZnGa₂O₄ ceramics are synthesized, for the first time, by combining high-energy ball milling, solid-state reaction and spark plasma sintering. They appear transparent in both the visible and near infrared (up to 9 μm) ranges after a post-SPS annealing in air converting the raw semiconductor into an electrical insulator. The maximum of transmittance is reached in the near infrared region, at around 2.5 μm, with a value of 78 % (1 mm thick sample) close to the maximum value of transmittance previously measured for single crystals. These transparent ceramics present a classic cubic spinel ZnGa₂O₄ structure and a dense microstructure (> 99 %) attained without sintering aids, with an average grain size of 600 nm and a random orientation of the crystallites. TEM observations performed on thin foils have revealed limited nanometer scale intergranular porosity which does not affect much the transparency. As a proof of interest, red long-lasting luminescence arising from the entire sample volume is observed in these Cr³⁺ doped transparent ceramics. This innovative work is anticipated to further drive the development of transparent ZnGa₂O₄ ceramics towards a wider range of performing optical applications such as laser emission.     

Amelioration on energy storage performance of KNN-based transparent ceramics by optimizing the polarization and breakdown strength

Transparent ceramic capacitors have broad application prospects in electronic devices due to their excellent optical transparency and energy storage properties. However, the low polarizability and high remnant polarization of the existing transparent dielectric ceramics limit the promotion of energy storage performance. Here, Bi(Li_0.5Nb_0.5)O₃ (BLN) was chosen to modify the (K_0.5Na_0.5)NbO₃ (KNN)-based ceramics to optimize the optical transmittance and energy storage characteristics simultaneously. On the one hand, the grain growth is inhibited, contributing to the improved breakdown strength and transmittance. On the other hand, the doping BLN could reduce the polar nanoregions size, which makes them respond more quickly to the external electric field and, thus, improves the energy storage efficiency. As a consequence, 0.95KNN–0.05BLN ceramic possesses the excellent W_rec of 4.39 J/cm³, η of 81.4%, and transparency of 77.9% with an average grain size of ∼109 nm. This work opens up a paradigm to develop a transparent pulse capacitor.     

Optical properties of transparent polycrystalline ruby (Cr:Al2O3) fabricated by high-pressure spark plasma sintering

Doped transparent ceramics with high optical quality can serve as materials for photonic applications such as laser gain media. In that regard, transparent polycrystalline alumina has potential for high-power applications due to its excellent physical and chemical properties, combined with unique doping possibilities. However, optical birefringence of Al₂O₃ crystals make achieving sufficiently high optical transmittance a processing challenge. In the present study, we demonstrated fabrication of highly transparent 0.5 at.% Cr:Al₂O₃ ceramics by high-pressure spark plasma sintering (HPSPS). The optical properties of these polycrystalline ruby ceramics were analyzed in order to assess possible laser operation (at 694.3 nm). The obtained ceramics exhibit high in-line transmittance (～72.5 % at 700 nm), equivalent to a scattering coefficient of 2.15 cm^?1, and characteristic ruby photoluminescence. The theoretically estimated lasing threshold and percentage of absorbed pump power indicate that such ruby ceramic lasers could operate at reasonable thresholds of 80?225 mW with short lengths of 0.5?5 mm. Thus, HPSPS is a promising method for producing laser-quality doped transparent ceramics for compact laser systems.     

Transparent semi-crystalline polymeric materials and their nanocomposites: A review

Optical transparency is an important property for a material, especially in certain fields like packaging, glazing, and displays. Existing commercial transparent polymeric materials are mostly amorphous. Semicrystalline polymers have often-superior chemical resistance and mechanical properties particularly at elevated temperatures or after solid-state drawing but they appear opaque or white in most cases. This review describes the present state-of-the-art of methodologies of fabricating optically transparent materials from semicrystalline polymers. A distinction is made between isotropic, biaxially stretched, and uniaxially stretched semicrystalline polymers. Furthermore, some functionalities of transparent nanocomposites based on semicrystalline polymers are also discussed. This review aims to provide guidelines regarding the principles of manufacturing transparent high-performance semicrystalline polymers and their nanocomposites for potential applications in fields like packaging, building, and construction, aerospace, automotive, and opto-electronics.     

Optical,mechanical and fractographic response of transparent alumina ceramics on erbium doping

Alumina ceramics found their utilisation in many applications which can be further extend by attaining functional properties; in our case the transparency obtained through precise processing and photoluminescence due to erbium (Er) doping. In order to examine the optical, mechanical and fractographic response of transparent alumina on Er doping, slip casted samples containing 0–0.15 at.% of erbium nano-oxide were pre-sintered by two-step sintering regime and then hot isostatically pressed. Prepared samples exhibited fully dense submicron microstructure and corresponding high transparency (RIT up to 60%). Positive influence of doping on the Vickers hardness resulted in values up to 27 GPa (at 10 N load). Moreover, the comparison of the Vickers hardness determined at different loadings with literature data showed that the Er doped alumina is one of the hardest material in this category. The samples were characterised also in terms of fracture toughness and fractographic behaviour.