  We report absorption and photoluminescence spectra of Si and SnO$_2$
polycrystalline nanofilms in the UV-Vis-NIR range, featuring discrete bands
resulting from transverse quantum confinement. The film thickness ranged 3.9 nm
to 12.2 nm, depending on the material. The results are interpreted within the
particle-in-a-box model, with the box width equal to the layer mass thickness.
The energy levels and transitions scale as the inverse square of the film
thickness. The calculated values of the effective electron mass are independent
on the film thickness and equal to 0.17m$_o$ (Si) and 0.21m$_o$ (SnO$_2$), with
m$_o$ the mass of the free electron. The uncertainties in the effective mass
values are ca. 2.5%, determined by the film thickness calibration. The second
calculated model parameter, the quantum number $n$ of the HOMO, was also
thickness-independent: 8.00 (Si) and 7.00 (SnO$_2$). This indicates that the
Fermi level should also scale as the inverse square of the film thickness in
these nanofilms. The observed transitions all start at the level $n$ and
correspond to {\Delta}$n$ = 1, 2, 3, etc. The photoluminescence bands exhibit
large Stokes shifts, moving to higher energies with increased excitation
energy. The photoluminescence quantum yields exceed unity, showing evidence of
multiple exciton generation from each absorbed photon. A prototype Si-SnO$_2$
nanofilm photovoltaic cell demonstrated an increase of the photoelectron yield
with the photon energy, showing evidence of multiple exciton generation.
