Photoluminescence of mesoporous silica molecular sieves

Mesoporous silica molecular sieves (MCM-41), which are a mixture of microtubules and hexagonal prisms, were prepared by a hydrothermal self-organizing method under acidic conditions. The nanostructure of silica was characterized by scanning electron microscope and transmission electron microscope. The composition of the sample was analyzed by Infrared spectra, Raman spectra, and energy-dispersed x-ray spectra. The photoluminescence spectrum shows that a broad emission band appears in the wavelength range from 400 to 800 nm, which consists of two broad emission subbands, one at 477 nm and the other at 512 nm. The visible luminescence appearing in calcined MCM-41 silica is ascribed to significant amounts of the twofold coordinated silicon centers (Si20).