Luminescence properties of nonbridging oxygen hole centers at the silica surface

Two variants of the surface-nonbridging oxygen hole center, („Si–O)3Si–O and („Si–O)2(H–O)Si–O , stabilized in porous films of silica nano-particles were investigated by time resolved luminescence excited in the visible and UV spectral range by a tunable laser system. Both defects emit a photoluminescence around 2.0 eV with an excitation spectrum evidencing two maxima at 2.0 and 4.8 eV, this emission decreases by a factor 2 on increasing the temperature from 8 up to 290 K. However, the different local structure influences the emission lineshape, the quantum yield and the deca