Titanium Centers Induced in Borate Glasses by Irradiation

The electron paramagnetic resonance of alkali borate glasses containing Ti was observed at 9.1 GHz before and after room-temperature X irradiation. The irradiation-induced spectra can be separated into (1) the well-known complex borate resonance with an average g value greater than that of the free electron (2.0028) and (2) a resonance with a lower g value. The latter resonance consists of two asymmetric ESR lines, one broad and the other narrow, whose characteristics are reported. These lines were not observed in the corresponding Ti-free base glasses; they arise from induced Ti centers. The broad asymmetric line ( T ₁) corresponds to a Ti^3.1 ion in sixfold coordination, whereas the narrow asymmetric line ( T ₂) corresponds to a Ti³⁺ ion in a different structural configuration. Lines T ₁ and T ₂ are stable at room temperature, not easily saturated with microwave power, and exhibit behavior independent of the complex borate resonance. The total relative intensity of these lines depends on the total Ti concentration in the glass, the Ti⁴⁺/Ti³⁺ ratio in the glass before irradiation, and the structure of the glass.