The penetration depth of UV monochromatic light into deposited TiO2 anatase powder was investigated. The
light penetration depth was considered in units of numbers of surface hole, Ns, and electron, NO2, centers
activated during irradiation. The numbers of hole centers Ns were obtained from photostimulated oxygen isotope
exchange reaction registered by means of mass spectrometry. The numbers of electron centers NO2 were obtained
from subsequent thermo-programmed desorption spectroscopy of photoadsorbed oxygen O−
2 . It was shown that
the depth D of UV light penetration into UV absorbing TiO2 powder coat depends on the wavelength and intensity I0 of incident UV light and obeys to the equation D(I0) = 1
keff lg(I0/Im) obtained from the Beer–Lambert–Bouguer law with effective extinction coefficient keff and minimal value of light intensity Im, below
which the photoactivation is considered negligible. Commonly, the value Im has an order of a few microwatts/
cm2 for activation of electron and hole type centers except for a case of 334 nm falling into the band of the first
direct band-to-band transition of anatase, where relatively high threshold value Im=0.063 mW/cm2 for photoactivation of hole centers was revealed. Effective extinction coefficient keff may be considered proportional to the
absorption coefficient of TiO2 in the region of fundamental absorption, whereas, in the non-fundamental absorption region, keff exceeds significantly that of TiO2 due to, probably, dominating scattering processes. At small
intensities of the incident light, there is a strong sensitivity of the penetration depth (and activated surface) to the
intensity.