Controlled Massively Defective Crystalline Solutions with the Fluorite Structure

Fluorite‐structure compounds form a rare example of ionic species containing vacancies and interstitials in very high concentrations (up to 50 mole‐%). With the formation of substitutional defects incorporating the "half‐breed" derivatives of the type (Ln = lanthanon and yttrium) the possibility of controlling a whole series of properties of fluorite for applications such as lasers is apparent. Crystalline solubility is extensive in binary systems of the type , , and , and in ternary systems . Unit cell dimension, density, and refractive index measurements confirm the existence of interstitial F − as the major defect in and type structures, while simple substitutional defect structures exist between and . Ternary compositions can show a controlled combination of the two types of defect. Certain of the crystalline solutions have been shown to exhibit photoluminescence and cathodoluminescence.