Europium and samarium doped fluorochlorozirconate (FCZ) glasses for optoelectronics applications: thermal and optical properties

Abstract

Fluorochlorozirconate (FCZ) glasses are a member of heavy metal fluoride glasses, and are derived from a well known ZBLAN glass. In this work, halogen salts of europium (Eu2+) and samarium (Sm3+) are used as dopants in FCZ glasses. FCZ glasses doped with Eu2+ and Sm3+ can be used in high resolution x-ray imaging for tissue scanning, and have been shown to behave as storage phosphors and/or x-ray scintillators. Glass transition (Tg), heat capacity (Cp) and glass crystallization (Tc) properties of Eu2+ and Sm3+ doped and undoped FCZ glasses with different amounts of relative Cl concentration, that is, with respect to the total Cl and F concentration have been investigated by conventional differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC) techniques. MDSC experiments were performed at different heating rates to analyze the complex transitions and to get a better resolution of any overlapping transitions. The crystallization kinetics have also been studied by applying the Kissinger technique to multiple DSC scans in order to determine the thermal stability of FCZ glass samples used in this work. The apparent activation energy for the crystallization process was obtained by the crystallization peak temperature shift method in the conventional DSC mode. The specific heat capacity (Cp) has been measured as a function of composition, and the glass transition temperature (Tg) is evaluated from the smooth change in the heat capacity curve during the glass transformation. The observation of two possible glass transitions points to the presence of two phases in these FCZ glasses with higher relative Cl content. Optical transmission spectra of both doped and undoped FCZ glass samples have been measured by infrared spectroscopy and optical band gaps corresponding to an absorption coefficient of 103 cm-1 have been determined. A good correlation between X-ray luminescence and the glass structure is observed. While the integrated photoluminescence intensity increases linearly with the Sm3+ concentration, the integrated X-ray luminescence increases sublinearly. The importance of appropriate annealing conditions, such as temperature, time and ambient atmosphere, and their effect on the X-ray luminescence of rare earth (RE) doped FCZ glass samples have been investigated. Annealing conditions influence the formation of BaCl2 nanocrystals in the glass and the properties of the resulting FCZ glass ceramics.