The W 4f photoemission spectra of NC films that have been electrochemically charged show significant populations of tungsten in more reduced states. All NC films show a doublet (W B ) of varying intensity 1.4-1.5 eV lower in binding energy than the highest energy W 4f doublet (W A ). In addition to W B , films reduced in Li + and Na + electrolytes show another doublet (W C ) 2.2 eV lower in binding energy than W A . The XP spectra of these films also show higher intensity in both low binding energy doublets, indicating a much larger population of both reduced tungsten states compared to the other samples. The more dominant presence of reduced tungsten species could be interpreted as a greater amount of charge stored on tungsten cations in the material. Differing amounts of charge localization helps explain the differences in the electrochromic line shapes between samples. Greater charge localization as a function of lithium-ion intercalation has been used to explain increased visible light electrochromism in niobium oxide NCs as well. This supports our hypothesis that the visible light absorption of Cs:WO3 NCs comes from the localization of charge during the double injection of electrons and cations into the material. The small increase in reduced tungsten species for films reduced in K + and TBA + electrolytes could either be due to a small amount of the reduction of surface tungsten atoms, or it could be the result of final-state effects that become more influential at higher carrier concentrations.