Fluorescence of Pd-doped Ti:CMAS glass and glass-ceramics

Room- and low (liquid nitrogen)-temperature fluorescence is measured for novel Pd-doped Ti-containing calcium magnesium aluminosilicate (Ti:CMAS) glasses and glass-ceramics prepared in air and forming gas atmospheres. A broad fluorescence peak at \textasciitilde 560 nm from F$+$ color centers, observed at 77 K in Pd-free and Pd-doped Ti:CMAS parent glasses under the excitation wavelengths of 300-320 nm, suggests the presence of significant concentration of oxygen defects in the vicinity of titanium ions. These defective titanium octahedra (TiOn, n\textless 6) are assumed to be found in close proximity in the structure of parent glasses. Glass-ceramics made in forming gas do not show any fluorescence at all, while the samples ceramized in air show blue emission at \textasciitilde 490 nm at the liquid nitrogen temperature under the excitation wavelengths of 260-280 nm. This fluorescence is associated with a UV-excited charge-transfer transition from the 2p orbits of the surrounding oxygen ion to the vacant outer 3d orbit of Ti4$+$, followed by the radiative annihilation.