  Over the ten past years, various experimental studies of solid solutions A
1-x B x XO 4 (e.g. A = Sr, B = Pb, X = W) with scheelite structures have
evidenced correlations between structural, vibrational modifications due to
chemical substitution, and increasing photoluminescence intensities under UV or
X-ray excitation. We propose a simple semi-empirical approach based on local
zones with different compositions, allowing simulating the variations of
structural, vibrational and photoluminescence characteristics, in the full
composition range 0$\le$x$\le$1. The structural characteristics are cell
parameters, cell distortions or crystallite size effect, Debye-Waller factors,
Raman shifts characterizing vibrations and photoluminescence signals under UV
or X-ray excitations. Each property is assumed to be represented by a
non-linear function Y(x) depending on composition x and on local
microstructural disorder. To illustrate this approach based on the coexistence
of local zones with different compositions, we have fitted the Y(x) function to
experimental data, which allowed us determining the significant parameters
characteristic of the series with A=Sr, B=Pb and X = W. These parameters
deliver a new microstructural interpretation of the increasing
photoluminescence intensities observed for intermediate composition x in solid
solutions. A generalization of this approach to other series of solid solutions
is quite possible.
