Glass composition dependence of luminescence due to Ge2+ center in germanate glasses

Germanate glasses were prepared by the melt-quenching method using an assembled hot-thermocoupler equipped in a sample chamber of a fluorescence spectrometer, and subsequently their luminescence and excitation spectra were measured. In the GeO2 glass, luminescence bands due to the Ge2+ center appeared at the central wavelengths of 300 and 395 nm, their excitation bands being at 250 and 330 nm, respectively. In the (100 − x)GeO2 − xMmOn glasses, for MmOn = B2O3 (x ≦ 50), SiO2 (x ≦ 40), and Al2O3 (x ≦ 2), the luminescence intensity and therefore the amount of the Ge2+ center increased with increasing the content of MmOn, where M(2n/m)+ ions (B3+, Si4+, and Al3+) have lower basicities than a Ge4+ ion. Contrarily, for MmOn = Li2O (x ≦ 30), Na2O (x ≦ 20), K2O (x ≦ 20), CaO (x ≦ 20), SrO (x ≦ 3), BaO (x ≦ 15), ZnO (x ≦ 20), Ga2O3 (x ≦ 10), Sb2O3 (x ≦ 20), Bi2O3 (15 ≦ x ≦ 25), TiO2 (x ≦ 3), and Nb2O5 (x ≦ 10), the luminescence intensity and the amount of the Ge2+ center rapidly decreased with increasing the amount of additives and disappeared, where M(2n/m)+ ions (Li+, Na+, K+, Ca2+, Sr2+, Ba2+, Zn2+, Ga3+, Sb3+, Bi3+, Ti4+, and Nb5+) have higher basicities than a Ge4+ ion.