Extinction of photo-induced Ti3+ centres in titanium oxide gels and gel-based oxo-PHEMA hybrids

We report on extinction measurements of photo-induced Ti3+ centres in titanium oxide gels and gel-based organic–inorganic hybrids. Simultaneous absorption and EPR experiments have been carried out. Despite of an expected heterogeneous origin of the absorption band, the electronic traps population is found pure statistical: it can be characterised by effective extinction coefficients ε ¯ = 780 cm - 1 M - 1 (gel) and ε ¯ = 340 cm - 1 M - 1 (hybrid) in the maximum of the absorption continua, respectively, at 600 nm and 640 nm. Using these values, an extremely high concentration of long-lived trapped electron exceeding 1020 cm−3 has been evidenced in these materials.