These localized electrons on tungsten cations lead to a higher energy optical absorption feature due to polaronic hopping, or charge transfer between different tungsten species in the material. The presence of localized electrons is evidenced by the increase in lower binding energy components in the W 4f photoemission spectra for these films. Complementary experiments to probe the overall change in tungsten oxidation state (e.g. by near-edge X-ray absorption spectroscopy) would help validate these connections between the reduction conditions, the electronic state of the material, and the electrochromic spectral response. The distinct spectral response based on the electrolyte cation used opens new possibilities for tuning the spectral selectivity of smart window devices to overlap with the different regions of solar radiation.