Polycrystalline Optical Material Group | Research Center for Electronic and Optical Materials

MORITA, Koji / Group Leader

MORITA.Koji@nims.go.jp

MORITA's SAMURAI page

Development of complex polycrystalline optical ceramics and its bulk processing

Overview

Optical ceramics are important key components for sensor window and high-brightness light source optical materials for realizing a highly efficient, safe, and secure society. To achieve a breakthrough for realizing next-generation optical functional materials that satisfy those requirements, the challenging approach for developing new materials would be essential. Therefore, in addition to conventional simple component system, we are now conducting research on the development of new complex composite optical materials called as "medium-entropy" and "high-entropy" systems, as a challenging area that will realize breakthroughs in the field of optical ceramics. We are challenging ourselves with the synthesis of functional powders and the development of processes for creating polycrystalline optical devices from powders. This research is aiming to achieve from the synthesis of functional powders to the development of bulk processing of polycrystalline optical devices from the functional powders.
In particular, in order to realizing sensing applications, our research focus on the synthesis of complex compositional fluorescence powders, polycrystalline optical materials that possess broadband emission and transmittance from the visible to near-infrared (>1000 nm) range, as well as the development of its bulking processes for those functional powders.

Characteristics

• Broadband traneparent materials from visible to near-infrared region
• Development of complex polycrystalline optical materials
• Development of a new bulk processing for realizing transparent polycrustalline ceramics
• Optical materials that simultaneously posess optical and structural properties
• Infrared phosphors and its bulk processing

Major reserch

For industrial applications as optical window materials and sensors, excellent mechanical and thermal properties are essential in addition to optical properties. However, it is not easy to realize multiple functional optical materials by simple component system, and hence, composite materials (CMC: Ceramic Matrix Composite) by combining several materials with different functional properties would be necessary. For example, the left figure shows a layered optical CMC ceramic with high strength and broadband transmission properties, which a high-hardness α-Al₂O₃ alumina phase was layered on the surface of the infrared transparent MgAl₂O₄ spinel. This material achieveded excellent broadband transmission properties while superimposing mechanical properties (high hardness) of 2.0 to 2.5 times greater than conventional materials. The realization of this multilayer optical material was achieved by optimizing the synthesis process and achieving a good bonding interface.

In the field of optoceramics, development of new material systems that achieve breakthroughs in the optical ceramics for opening new research areas. Recently, high-entropy ceramics that are fromed by mixing of the elements more than 5 elements has attracted attention. The researches of the high-entropy have firstly been conducted mainly in metallic materials, and new excellent functional properties have been reported. However, in recent years, the optical ceramics has also been confirmed in high-entropy ceramics. We have also succeeded to attain high-entropy broadband transparent polycrystalline ceramics, that posess laser oscillation and fluorescence by using homemade homogeneous and fine high-entropy powders.

Summary

Polycrystalline optical ceramics, that can fabricate from powder materials using sintering techniques, can realize low cost, productivity, and large size, net shaping into the final form, as well as excellent mechanical properties. Furthermore, flexible microstructure design, including composition control, compounding with different phase, and refining the microstructure, enable to improve the properties enough for industrial applications.

LI, Jiguang

LI.Jiguang@nims.go.jp

LI's SAMURAI page

Inorganic optical materials

Overview

Phosphors and transparent ceramics are optically functional materials that are finding wide applications in LED lighting, display, solid state lasers, and scintillation.
The current advances in the above technological fields are imposing a strong need for new materials and fabrication technologies to achieve cost reduction and improved/novel optical properties.

Characteristics

Through rational design of precursors and synthesis technologies, highly sinterable ceramics powders that can be fully densified at significantly reduced temperatures can be produced Through morphology control of the crystallites (size/shape/exposed facets), improved/novel luminescence properties can be attained Through polyhedron design of the activator ion and composition/structure design of the host lattice, high performance new phosphors can be expected

Major reserch

1. Figure shows multicolor emitting (Gd,Ln)₃(Al,M1/M2)₅O₁₂:R³⁺phosphors, where Ln is a lanthanide element, M1 and M2 are 2+ and 4+ charged dopant ions, respectively, and RE³⁺is an activator ion. The compounds were derived by modifying the Gd and Al sites of Gd₃Al₅O₁₂ garnet (GAG), and such a strategy not only stabilized the metastable lattice of GAG but also produced multicolor luminescence by doping different types of activators.
2. Figure shows the (Y,Gd)₂O₃:Eu³⁺transparent ceramics, which were fabricated via vacuum sintering at only 1700 °C for 4 h but are as transparent as the corresponding single crystals. The oxide powders used for sintering were obtained by engineering of layered hydroxide nanosheets, including composition design and thickness control, followed by proper calcination. The derived oxide particles showed high dispersion, high specific surface area and unimodal size distribution, revealing the significant advantages of the synthesis technology.

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Summary

The ultimate goal of research is to develop advanced phosphors and transparent ceramics for application in the important fields of lighting/display, solid laser and scintillation (imaging), which is largely based on controllable processing of powders and rational design of chemical composition and crystal structure of the materials.

VASYLKIV, Oleg

Oleg.VASYLKIV@nims.go.jp

VASYLKIV, Oleg's SAMURAI page

Deformation-resistant multipurpose ultra-hight temperature ceramics

Overview

We are currently conducting research in the chemical structural engineering of deformation-resistant UHTC carbides, borides, nitrides, and composites with ultra-hardness and ultra-high strength.
We have combined the merits of powder synthesis and electric current activated sintering technique for the design of techniques applied on powder body with establishing morpho-structural and compositional features, which lead to the fabrication of bulk ceramics with superior characteristics.

Characteristics

• multipurpose deformation-resistant UHTC carbides, borides, nitrides and composites
• sufficient balance between ultra-high hardness, ultra-strength, toughness and modulus
• morpho-structural and compositional features with superior characteristics
• gas turbine operation in a combined cycle power plants

Major reserch

Summary

The request for new multipurpose deformation-resistant ultra-high temperature ceramics (UHTC), able to act as special engine and vehicle protection, ceramic segmented leading edge components for aerospace, plasma-facing, ceramic parts for solar towers used for gas turbine operation in a combined cycle power plants (grids, superheaters, reheaters, evaporators, steam turbines, condensers, and chimneys) cause the worldwide demand in a new class of ceramic composites of incredible high strength, the sufficient balance between high toughness, hardness, and high-modulus.