α-Sialon and β-Sialon phosphors activated by Eu²⁺ are suitable for white LEDs used as LCD backlights and illuminations because of their excellent properties such as long-term reliability and small temperature dependency of photoluminescence emission intensity. α-Sialon phosphor emits yellow/orange fluorescent light and β-Sialon phosphor emits green fluorescent light.

During firing by the gas pressure sintering method, the emission intensity of β-Sialon phosphor was increased with grain growth by Ostwald ripening. We succeeded in improvement of the emission intensity by optimizing synthesis conditions, and the emission intensity can be increased three times more. β-Sialon phosphor is adopted for backlights of LED TV.

The emission wavelength of α-Sialon phosphor can be tuned from yellow to orange by composition tailoring. Amber color LED devices were demonstrated using orange α-Sialon phosphor. It is suitable for winkers of automobiles and adopted for this application.

Size tuning of colloidal Co-Al layered double hydroxide (LDH) nanoparticles has been demonstrated by a dialysis treatment. Starting from colloidal dispersion of LDH nanoparticles with diameter of ~10 nm, dialysis treatment under an ambient condition was found to allow for fine tuning of the particle in the size of 10-20 nm. With an increased time of dialysis treatment, the size of Co-Al LDH nanoparticles increases because of acceleration of dissolution-recrystallization. The colloidal Co-Al LDH nanoparticles exhibit high dispersion stability free from particle aggregation even after the dialysis treatment. Co-Al LDH films oriented on a substrate were successfully prepared by coating the dialyzed crystals with an anisotropic plate-like morphology.

The author received 2019 JSPM Award for Distinguished Achievements in “Development for fundamental research for production of Nd-Fe-B permanent magnet materials.” This paper summarizes the recipient’s works that led to this honor. In the development of isotropic nanocomposite magnets in the Nd－Fe－B－Ti－C system, he developed the concept of the kinetic control of the phases in the rapid solidification process. In addition, the author describes some of the problems that was unsolvable in the early research on the coercive force mechanism of the Nd－Fe－B permanent magnets, and how these problems have been solved as a result of the deepening of the basic science of permanent magnets by many researchers in the “Elements Strategy Research Center for Magnetic Materials,” a project of the Ministry of Education, Culture, Sports, Science and Technology of Japan, of which he has been the directing investigator. These theoretical results are expected to contribute as a basis for future data-driven research to future industry-university collaborative activities.

La-Co co-substituted magnetoplumbite-type ferrite is a base material used for high-performance ferrite magnets. The presence of small amount of Co²⁺ dramatically improves the coercivity. The unquenched angular moment of Co²⁺ must enhance the uniaxial anisotropy of M-type ferrite, however, the Co occupation site, i.e., the oxygen coordination, which is the key of the magnetic anisotropy, has not been revealed. We review the series of works to identify the Co substituted site in La-Co co-substituted magnetoplumbite-type ferrite.

The itinerant ferromagnetism is reported in A₂T₁₂P₇ (A = lanthanoid, Group 2-4 element, T = transition metal) with Zr₂Fe₁₂P₇-type structure. In order to investigate the behavior of electrons in this structure, we have synthesized single crystals of (Ca_1-xMg_x)₂Co₁₂P₇ and measured magnetizations. From magnetic susceptibility, we found that Ca₂Co₁₂P₇ shows a ferromagnetic transition at T_C = 78 K, which is attributed to the Co-3d itinerant electrons. We also found the Curie temperature decreases and eventually disappears around x~0.6, when Ca is substituted by Mg. It has been suggested that the electronic density of states changes and the magnetic state of this system crosses the quantum critical point due to the positive chemical-pressure effect of the Ca substitution by Mg.