Red and near-infrared photoluminescence from silica-based nanoscale materials: Experimental investigation and quantum-chemical modeling

Experimental study of room temperature photoluminescence (PL) from silica nanoparticles and mesoporous silicas induced by ultraviolet and visible laser light (λEXC=266 and 532 nm or 4.66 and 2.33 eV, respectively) reveals several well-defined PL bands in the red- and near-infrared spectral range, which are peaked at 1.905, 1.78, 1.61, 1.40, 1.27, and 1.14 eV. The relative intensities of the bands depend on the specimen heat pretreatment temperature and excitation wavelength. The band at 1.905 eV shows all conceivable characteristics of nonbridging oxygen (NBO) defects in bulk silica, so it can be assigned to the same species in nanometer-sized SiO2 fragments. The more slowly decayed 1.78-eV band was assigned to NBOs incorporated into distorted SiO4 tetrahedrons on the surface. The 1.14–1.61 eV PL bands can be observed mainly with 2.33-eV excitation for heat-pretreated specimens (Tht=873 and 1173 K) and can also be associated with NBOs. The red shift of these bands is explained in terms of formation of com...