Charge ordering and optical transitions of ${\mathrm{LiV}}_2{\mathrm{O}}_5$ and ${\mathrm{NaV}}_2{\mathrm{O}}_5$

We present measurements of the polarized optical spectra of ${\mathrm{NaV}}_2{\mathrm{O}}_5$ and ${\mathrm{LiV}}_2{\mathrm{O}}_5.$ In an energy range from 0.5 to 5.5 eV, we observe similar peaks in the $E\Vert a$ spectra of ${\mathrm{NaV}}_2{\mathrm{O}}_5$ and ${\mathrm{LiV}}_2{\mathrm{O}}_5,$ which suggests similar electronic structures along the a axis in both materials. On the other hand, we find an almost complete suppression of the peaks in ${\sigma }_b$ of ${\mathrm{LiV}}_2{\mathrm{O}}_5$ around 1 and 5 eV. We attribute this suppression to the charge localization effect originating from the existence of a double-chain charge-ordering pattern in ${\mathrm{LiV}}_2{\mathrm{O}}_5.$