  Samples of nitrogen-doped titanium dioxide (anatase, $0.2 \leq N \leq
1.0~wt\%$) prepared by the sol-gel method were investigated using X-band EPR
spectroscopy, photoconductivity and photocatalysis measurements. $N\bullet$ and
$NO\bullet$ paramagnetic defects in N-TiO2 have been observed; their
concentrations and spin-Hamiltonian parameters were calculated. An increase
both in the rate of the generation of free charge carriers and in the rate of
photocatalysis was found in N-TiO2 in contrast with non-doped titania under
visible light. The correlation of the density of the observed radicals with the
photoconductivity and photocatalysis data is discussed.
