  We consider two equations for the filling factor estimation of infiltrated
zinc oxide (ZnO) in silica (SiO_2) opal and gallium nitride in ZnO opal. The
first equation is based on the effective medium approximation, while the second
one - on Maxwell-Garnett approximation. The comparison between two filling
factors shows that both equations can be equally used for the estimation of the
quantity of infiltrated nanocrystals inside opal matrix.
