Researchers have created a new type of transparent ceramics

With good transparency, mechanical properties and thermal conductivity, transparent ceramic materials have become a very important class of "structure function integration" ceramic materials, but they usually need to be prepared by high-temperature sintering above 1000 ℃.
 
The fluorescent conversion material based on inorganic transparent ceramic matrix is used in high-power LED (light emitting diode), light-emitting diode）、 Laser lighting, laser display, scintillator and other optoelectronic devices have the ability that other materials can not replace.
 
However, the high sintering temperature of transparent ceramics on the one hand leads to the fact that many advanced phosphors cannot be burned completely alone; On the other hand, the interface reaction between the phosphor and the transparent ceramic substrate at high temperature will also make the composite ceramics impermeable, which hinders the application of all inorganic fluorescent conversion materials in the field of high-power and high-density laser devices.
 
After taking note of the above situation, Professor fanyuchi of Donghua University set up a project, hoping to solve the above pain points.
 
Through the cooperation with Professor xiazhiguo of South China University of technology, they sintered CaF₂ transparent ceramics with high visible light transmittance at 350 ℃. By using this low-temperature sintering technology, it is easy to realize the composite of transparent ceramic matrix and phosphors such as caalsin3: Eu²⁺with excellent luminescent properties but low thermal stability, and avoid the loss of properties of phosphors due to interface reaction.
 
Due to the optical isotropy of CaF₂ ceramic, the fluorescent converter based on this transparent ceramic shows a color rendering index of 92 and a light effect of 120lmw^-1, and can be developed into a universal matrix material, which can be used in the fields of high-power LED, high-density laser lighting and stimulated fluorescence display.
 
In the research, they prepared fluoride transparent ceramics by cold sintering technology, which can be regarded as a universal platform for the preparation of fluorescent bulk materials, and it can be compatible with most fluorescent powders including rare earth phosphors and semiconductor quantum dots.
 
They have also encountered some problems in the preparation of transparent ceramic matrix. For example, when choosing cold sintering additives at first, they made a lot of attempts and finally found that hydrochloric acid with a certain concentration had better dissolution and precipitation effect.
 
In addition, in the process of making fluorescent ceramics with fluorescent powder, they also encountered the problem of the fragility of ceramic blocks. For a long time, they could not get a complete block material, so they could not carry out subsequent performance tests.
 
After several discussions, the pressure, temperature and solvent concentration were adjusted repeatedly, and it took nearly two months. Finally, the preparation process was improved to obtain a complete block material.
 
Finally, relevant papers were published on advanced functional materials under the title of cold sintering of highly transparent calcium fluoride nano ceramic as a universal platform for high power lighting [1].
 

Figure 1 related papers (source: Advanced Functional Materials)

 
Fanyuchi said, "I think the following factors contributed to the success of this project: first of all, the first author, Dr. Gao Jie, is very diligent. He is the first student in the direction of cold sintering in our research group. He has strong hands-on ability and literature reading ability, and can continue to study in a new direction; second, the accumulation of the team. Professor Jiang Guan of our group has been deeply cultivated in the direction of ceramic sintering for many years, and has made many achievements in the direction of fluorescent ceramics, which has laid a good foundation for this project. Third, the strong alliance. Professor xiazhiguo of South China University of technology is an expert in inorganic luminescent materials, and has provided a lot of help for this project."
 
In addition, the reason why fanyuchi returned to China after studying in Japan was also influenced by Professor Jiang Guan. He said, "Mr. Jiang was my tutor during my graduate school and a returned overseas Chinese from Japan. When the country needed talents most, he gave up the preferential treatment abroad and returned home for development, and made a lot of achievements in powder metallurgy and ceramic preparation technology. The choice of the teacher also deeply infected and educated me. I deeply felt that only when a person combines his knowledge with the needs of the country and national construction can he best reflect his own value."
 
It is also reported that xiazhiguo once served as the spokesperson for europium (EU) in the international periodic table year (IYPT 2019). In response, he said: "I am honored to be the spokesperson for europium (EU) in the international periodic table year (IYPT 2019), because I have been engaged in the research of Eu²⁺ doped rare earth luminescent materials. It is a great encouragement for me to have this opportunity. I think on the one hand, we need to endure loneliness in the research. As for the traditional research field of Eu²⁺ doped rare earth luminescent materials, I have stuck to it for many years and made several very distinctive rare earth phosphors, including the well-known Eu²⁺ doped narrow-band green phosphors, Eu²⁺ doped oxide based red phosphors and Eu²⁺ doped near-infrared phosphors. On the other hand, if I had the opportunity to publicize my work, I should try my best. I submitted an application form for the spokesperson of europium (EU) to the Chinese chemical society at that time. The staff of the Chinese chemical society should have investigated my research background and finally gave me this opportunity. I am particularly grateful to the Chinese chemical society.
 
Reference:

1.Gao, J., Xia, Z., Ding, Q., Liu, Y., Yan, P., Hu, Y., ... & Jiang, W. (2023). Cold Sintering of Highly Transparent Calcium Fluoride Nanoceramic as a Universal Platform for High‐Power Lighting.Advanced Functional Materials, 2302088.

Website:研究人员造出新型透明陶瓷，可用于大功率LED、高密度激光照明领域 - 知乎