Spectroscopic assignments of Ti3+ and Ti4+ in titanium-doped OH- free low-silica calcium aluminosilicate glass and role of structural defects on the observed long lifetime and high fluorescence of Ti3+ ions

In this work we present the spectroscopic assignments of Ti3+ and Ti4+ in titanium-doped OH- free low-silica calcium aluminosilicate glass and the influence of structural defects on the observed long lifetime and high fluorescence intensity of Ti3+ ions. Measurements were performed with electron-spin resonance (ESR), time resolved luminescence, ultraviolet-visible (UV-VIS) optical excitation and emission spectra, and conventional optical absorption and photoconductivity. The ESR data showed that the Ti3+/Ti4+ ratio increases with the doping concentration and that the Ti3+ ions are in distorted octahedral sites. The assignment of the Ti3+ and Ti4+ emission bands derived from the spectroscopic results allowed us to propose a model explaining the mechanisms involved in the luminescence processes. The long lifetime of the Ti3+ emission around 650 nm (on the order of 170 mu s) is about two orders of magnitude higher than the values found in the literature and was associated to the trapping of the excited electrons by the glass defects followed by detrapping via defect recombination. In conclusion, the combination of several techniques permitted a comprehensive characterization of the Ti ions in this OH- free glass.