Effect of Microscopic Structure and Porosity on the Photoluminescence Properties of Silica Gels

Abstract

We have studied the photoluminescence (PL) characteristics of silica gels with different microscopic morphology, which are prepared by acid- and base-catalyzed hydrolysis of tetraethylorthosilicate in ethanol solution. All the gels show visible PL emission peaking at ∼420 nm after annealing the samples at ∼200 °C in air; however, the PL intensity and decay kinetics are strongly dependent on the microstructure and porosity of the initial gels. The annealing-induced PL intensity increases with decreasing porosity of the initial gels, whereas the PL decay dynamics tends to deviate from a pure exponential trend as the porosity of the initial gels becomes higher. These results indicate that the formation, stabilization, and radiative recombination process of the emission centers that are created during annealing are influenced by the microscopic morphology of the gels. These experimental results are interpreted in terms of the formation mechanism of the visible emission center in silica-based nanostructure materials proposed recently (Uchino, T.; Kurumoto, N.; Sagawa, N. Phys. Rev. B 2006, 73, 233203).