Thermal Evolutions to Glass-Ceramics Bearing Calcium Tungstate Crystals in Borate Glasses Doped with Photoluminescent Eu Ions.

Thermal evolutions of calcium-tungstate-borate glasses were investigated for the development of luminescent glass-ceramics by using Eu dopant in a borate glass matrix with calcium tungstate, which was expected to have a combined character of glass and ceramics. This study revealed that single-phase precipitation of CaWO crystals in borate glass matrix was possible by heat-treatment at a temperature higher than glass transition temperature for (100-) (33CaO-67BO)-CaWO ( = 8-15 mol%). Additionally, the crystallization of CaWO was found by Raman spectroscopy due to the formation of W=O double bondings of WO tetrahedra in the pristine glass despite starting with the higher calcium content of CaWO. Eu ions were excluded from the CaWO crystals and positioned in the borate glass phase as a stable site for them, which provided local environments in higher symmetry around Eu ions.