Thermal Evolutions to Glass-Ceramics Bearing Calcium Tungstate Crystals in Borate Glasses Doped with Photoluminescent Eu(3+) Ions

Thermal evolutions of calcium-tungstate-borate glasses were investigated for the development of luminescent glass-ceramics by using Eu(3+) 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(4) crystals in borate glass matrix was possible by heat-treatment at a temperature higher than glass transition temperature T(g) for (100−x) (33CaO-67B(2)O(3))−xCa(3)WO(6) (x = 8−15 mol%). Additionally, the crystallization of CaWO(4) was found by Raman spectroscopy due to the formation of W=O double bondings of WO(4) tetrahedra in the pristine glass despite starting with the higher calcium content of Ca(3)WO(6). Eu(3+) ions were excluded from the CaWO(4) crystals and positioned in the borate glass phase as a stable site for them, which provided local environments in higher symmetry around Eu(3+) ions.