Strong visible photoluminescence from SiO₂ nanotubes at room temperature

The optical studies of SiO] mesoporous materials with hierarchical tubules-within-tubule structure have been investigated by photoluminescence and Fourier-transform infrared transmittance (FTIR). Our results suggest that the radiative intensity can be strongly enhanced by annealing the samples in N₂ environment. From the FTIR spectra, we have pointed out that the origin responsible for the strong emission is Si-OH complexes located on nanotube surface. It has been observed that after turning off the pumping laser, the photoluminescence signal of SiO₂ nanotubes can persist for several seconds, which is much longer than that of most materials performed under similar conditions. We have found that the decay of the photoluminescence signal is due to the quantum tunneling process. These are triplet and singlet states of Si-OH complexes that are responsible for the observed persistent photoluminescence.