Phase Separation and Fluorescence Properties of Rare-Earth Doped Borosilicate Glasses

• Applicant: Dr.-Ing. Katrin Thieme
• Subject Area: Synthesis and Properties of Functional Materials
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 405862582

Nowadays, there is a high demand for materials possessing excellent optical properties and which are suitable for photonic applications. This proposal focuses on the preparation and characterization of fluorescent borosilicate glasses showing phase separation in borate-rich droplets surrounded by a silicate matrix, using the model system Na2O-B2O3-SiO2. Hence, the borate-rich droplets should be protected against chemical attack and degradation by the silicate matrix. Since the quantity of the droplet phases can be adjusted to be more than 30 %, the concentration of the rare-earth ions incorporated in one of the glassy phases will be significantly higher. The microstructure of the borosilicate glasses shall be adjusted by heat treatments leading to phase separation structures which vary in size, size distribution as well as the elemental distribution. The fluorescence properties, i.e. fluorescence intensity, emission wavelength, and fluorescence lifetimes, will be tailored by controlling size and composition of the respective phases. One of the main purposes of this project is to develop a general understanding of the influence of glass structure and composition of phase separated rare-earth containing borosilicate glasses on the fluorescence properties. Therefore, Na2O will be partially or totally replaced by different alkali or alkaline earth oxides, such as K2O, Cs2O, SrO, or BaO, and the effect on phase separation, especially on the formed structures will be studied. In order to obtain different structural glass parameters, such as network connectivity, structural units, and optical basicity of the glasses, the B2O3/SiO2 ratio shall be also varied. Since the optical basicity directly affects the local sites of the rare-earth ions, the luminescence properties will be influenced. The nano- and microstructure of the as-cast and heat treated samples will be comprehensively studied using electron microscopic analyses. Furthermore, the microstructure will be analyzed regarding size, size distribution, form, and number of droplets as a function of the supplied temperature/time schedule. Special attention will be paid to information about element distributions and chemical gradients. Since in rare-earth doped glasses, the fluorescence properties strongly depend on the coordination, concentration, and spatial distribution of luminescent ions, structural characterization techniques such as Raman, IR, and NMR spectroscopy shall be applied to gain a fundamental understanding of the rare-earth ion incorporation into these glasses and correlate the fluorescence properties to structural arrangements. The combination of structural characterization techniques and luminescence measurements will remarkably enhance the common understanding of the relationship between fluorescence properties and glass structure. These conclusions will help to develop new optical materials.

• DFG Programme: Research Grants