  The properties of polycrystalline wurtzite Zn_{1-x}Mg_{x}O (0 <= x <= 0.15)
have been studied, by powder X-ray diffraction, including an analysis of the
X-ray line-broadening, and by luminescence, absorption, and Raman
spectroscopies. We have previously established from synchrotron X-ray
difffraction that with increasing Mg-concentration, the c-axis compresses, and
the off-center cation displacement within each tetrahedral (Zn,Mg)O_{4} unit
decreases. Here we perform a size-strain line-broadening analysis of the XRD
peaks, which reveals that the Mg-substitution reduces the coherent crystallite
size and also develops the lattice microstrain. The optical properties of the
samples have been characterized by diffuse-reflectance spectroscopy and
fluorimetry. Both the optical band gap and the band-edge emission energies
gradually increase with the Mg-concentration in Zn_{1-x}Mg_{x}O. The
Mg-substituted samples show broader band tails near the absorption edge, due to
the increase of crystal imperfections. The peak broadening of the E_{2}{high}
Raman mode, upon the Mg-substitution, is also ascribed to the phonon shortening
lifetime mechanism via crystal defects.
