Mid-infrared lasers have been widely used in various fields, such as imaging, detection, diagnostics, environmental monitoring, medicine, industry, defense, etc. For mid-infrared laser systems, low phonon energy gain materials are key factors.

Among these mid-infrared materials, Er³⁺-doped CaF₂ transparent ceramics are promising candidate materials because of their ultra-low phonon energy as well as excellent physical, chemical, and optical properties, which quickly attract the attention of researchers. However, traditional preparation methods can’t obtain high-quality Er³⁺-doped CaF₂ transparent ceramics.

Recently, a research team led by Prof. ZHANG Long from the Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences has developed a high quality Er³⁺-doped CaF₂ transparent ceramics by single crystal ceramization. Their study was published in Journal of the European Ceramic Society.

In this research, the researchers grew the 3 at% Er³⁺-doped CaF₂ single crystal by the temperature gradient technique (TGT). The single crystal was cut into 5*5*3 mm³ cuboid, and put into a graphite mold. It undergoes plastic deformation and hot-pressing sintering in a vacuum hot press furnace, after which Er³⁺-doped CaF₂ transparent ceramic was obtained. The ceramic sample was polished to 1-mm for characterization.

They discovered that the Er3+-doped CaF₂ transparent ceramics possess obvious polycrystalline structure, perfect transmittance, and excellent mid-infrared performance, which are better than that of hot-pressed and hot-formed Er³⁺-doped CaF₂ ceramics.

In addition, the influencing factor for the slight change of Er³⁺-doped CaF₂ transparent ceramics in optical performance was also discussed initially.

This work offers significant and wide-ranging opportunities for obtaining low phonon energy mid-infrared alkaline earth fluoride ceramic for future applications in mid-infrared lasers and amplifiers.