Nuclear magnetic resonance shows that under certain growth conditions hot-wire CVD a-Si:H grown at high rates contains a large amount of nanovoids. It was found that such nanovoids are filled with H-2 gas and the nanovoids are elongated with the along axis in the growth direction. Measured on the same samples photoluminescence (PL) showed that the tail-to-tail PL peak at 80 K was red-shifted significantly from 1.36 to 1.05 eV when the growth rate increases from 10 to 55 Angstrom/s. These studies indicate that the nanostructure is important to the behavior of PL in a-Si:H. (C) 2003 Elsevier Science B.V. All rights reserved.