Halide glasses

Abstract

An increasing interest is devoted to fluoride, and more generally, to halide glasses because of their potential use for making infra-red optical components and ultra-low-loss optical fibres. This paper presents the main fluoride systems based on ZrF 4, HfF 4, AlF 3, ZnF 2, on transition metals and on actinides and lanthanides, all of which act as glass progenitors. The main chloride glasses based on ZnCl 2, BiCl 3, ThCl 4 and CdCl 2 are also described. The aspects of glass synthesis reviewed include fluorination by NH 4HF 2 and reactive atmosphere processing, which are currently used to prepare and refine fluoride glasses. The manufacturing of glass samples and the drawing of fibres are discussed with the problems of nucleation and crystallization in mind. The characteristic temperatures for the major families of halide glasses are detailed in the text, but, generally speaking, the value of T G lies between 200 and 500° C for fluoride glasses and under 200° C for chloride and mixed halide glasses. The optical transmission range normally encompasses the U.V., visible and medium I.R. spectra. The position of the multiphonon absorption edge depends closely on the glass composition. The main optical characteristics are given and their potential use for making infra-red optical components, low-loss optical fibres, electrochemical barriers and laser hosts are presented and discussed. The occurrence of numerous new halide glasses provides experimental evidence for understanding the glass formation mechanism in non-oxide systems.