非酸化物ガラス-ガラスの形成と構造,およびガラス中の希土類イオンの光学的性質(第60回日本セラミックス協会学術賞受賞研究総説) Nonoxide Glass-Forming Systems-Glass Formation and Structure, and Optical Properties of Rare-Earth Ions in Glasses(Special Article: The 60th CerSJ Awards for Academic Achievements)

Nonoxide glasses composed of halides and/or chalcogenides (sulfides, selenides, and tellurides) as their main components have been extensively investigated due to their characteristic structures and properties. Among them, the present review focuses on glass formation based on nonfluoride-halide (halides other than fluoride) systems and the structure of the glasses as well as the transition properties of rare-earth ions in the nonoxide glasses. Systematic examination of glass formation in nonfluoride-halide systems based on AX_n-MX-M'X_2 with a single halide ion revealed that the systems of A=Zn, Cd, Ag, Cu and Li are vitrified by a conventional melting-cooling method, where X=Cl, Br, or I, M=alkali metal (K, Rb, Cs), and M'=alkaline earth metal (Ba). The coordination structure around the cations, A^<n+>, was investigated by means of X-ray absorption spectroscopy and other methods. The structural model for these halide glasses is also discussed. The studies about the transition properties of rare-earth ions in the nonoxide glasses showed that the multiphonon relaxation rates are strongly suppressed. Detailed analyses on the fluorescent decay curves for Er^<3+>-doped Ga_2S_3-based glasses are presented.