Fabrication of 3D structures using chemical vapor deposition of the ceramic eutectic system of solid state phosphors.

The eutectic structure of metals and ceramics occurs when several solid phases are separated from the liquid, creating a three-dimensional (3D) structure through spontaneous processes. Traditionally, it was believed that eutectic structures can be obtained by the melting process.

Yokohama National University (YNU) researchers have developed a chemical vapor deposition (CVD) process that allows lead gases to react and create solid materials with controlled properties in the YAG (yttrium alumina garnet)-alumina ceramic eutectic system.

In their study, they observed the growth of rod- and lamellar-shaped crystals in an alumina matrix on sapphire under Al-rich conditions. In contrast, under Y weights, they observed the growth of alumina-dominated crystals with a YAG matrix. The choice of the sapphire seed crystal and the structure of the precursor ensured the 3D structure. Compared to the solvent-solidification process, the CVD process expanded the variety of chemicals that could produce such reactions.

Chemically deposited YAG-alumina eutectics can be composed of other rare earth materials, which act as luminescent surfaces. For example, cerium ions emit yellow light when lit by blue LEDs, producing a white light for strong lighting. Europium ions emit red X-ray radiography light when exposed to X-rays passing through a semiconductor device. “Our experiments show how chemically preserved YAG-alumina eutectics can be used as environmentally friendly LED lighting and X-ray imaging,” says Yuri Mitsuhashi, the lead author of the study, who conducted the experiments as a graduate student at YNU.

Alumina has long been known as a strong ceramic material and is used in the production of optical and optical devices. Aluminum, including the rare earth aluminum garnets and perovskites, has been extensively studied as active ceramic materials, such as lasers, phosphors, and electronic devices. “Among the aluminates, the rare-earth aluminum garnets and perovskites have beautiful properties and fortunately have eutectic systems with aluminum,” says Shogen Matsumoto, who designed the lab’s X-ray machine for his PhD at YNU. He said, “We can make a crystal of matter that combines the advantages of alumina and aluminate.”

This shows that the formation of 3D structures in ceramic eutectic composites can be done not only through the melting process but also through the evaporation process. “CVD is ready to produce ceramic eutectic composites for functional or protective applications in the ground,” says Akihiko Ito, associate professor at YNU and principal investigator. “Contrary to this, the melting process, which requires a high temperature of more than 2,000 degrees Celsius to produce a ceramic coating on the substrate, is not effective. Further research will focus on elucidating the processes that produce chemically produced eutectics.”

Disclaimer: AAAS and EurekAlert! is not responsible for the accuracy of the news posted to EurekAlert! by supporting organizations or using any information through the EurekAlert system.