  Both theoretical and experimental analysis are carried out to understand the
underlying physics of the fascinating electronic and optical properties of
antimony tungstate (Sb$_2$WO$_6$). The nanosized ($\sim 40-80 nm$) material is
produced using hydrothermal method followed by the SEM and XRD analysis to find
the structural properties. The density functional calculation using PBEsol and
PBE exchange-correlations are compared with the experimental structural
parameters and PBEsol predicted crystal parameters and simulated XRD are in
excellent agreement with experimental results. The measured absorption spectra
in ultraviolet-visible range indicate the bandgap as $2.42 eV$, while, the
photoluminescence spectra reveal a gap of $2.65 eV$ . Using advanced density
functional theoretical (DFT) technique, the band structure and density of
states for Sb$_2$WO$_6$ are calculated and the calculated bandgap of $2.62 eV$
is in excellent agreement with the experimental finding. From theoretical
partial density of states calculations we identify that the bandgap is formed
between the O$-p_y$ orbitals bonded with Sb at valence band maxima and the
W$-d_{x^2-y^2}$ orbital at conduction band minima. The atomic level transitions
responsible for the peaks of absorption spectra and photoluminescence spectra
are identified as well by the means of DFT calculations. Following the matching
of theoretical and experimental observations, further calculation on optical
properties are carried out to reveal the plasma frequency corresponds to $13.36
eV$.
