| A new approach for studying thermal phase separation in sodium borosilicate glasses using Mn('2+) as a luminescent probe is investigated. Seventy-one samples of glasses activated by Mn('2+) inside and around the Na(,2)O(.)B(,2)O(,3)(.)SiO(,2) miscibility gaps were prepared. These samples were then phase separated by dry thermal treatment.;It is shown that on addition of MnO, the ternary Na(,2)O(.)B(,2)O(,3)(.)SiO(,2) system behaved like other quaternary systems of the type X(,2)O(.)MO(.)B(,2)O(,3)(.)SiO(,2) (X = Na, K; M = Mg, Ca, Ba, Zn). Scanning electron microscopy and X-ray microanalysis demonstrated that manganese concentrates preferentially in the boron-rich phase. This analysis, in conjunction with a comparison of Mn('2+) emission spectra of unheated and heat-treated glasses shows that the glasses are submicroscopically phase separated when prepared. The decay-time analysis of Mn('2+) luminescence indicates that the low energy emission band arises from Mn('2+) in the boron-rich phase while the high energy emission is due to Mn('2+) in the silica-rich phase. The difference in the crystal field parameters obtained from the excitation spectra of the two emission bands shows that the high energy emission band is from Mn('2+) in tetrahedral sites while the low energy emission band is from Mn('2+) in an octahedral environment. |
