Yellow tungsten oxide, also known as tungsten trioxide or WO3, can be made into an electrochromic film and used to produce an all-solid-state electrochromic device. Wherein, the discoloration mechanism of the WO3 film can be explained by the Schirmer model, that is, the small polaron model. That is because the scientists found that the small polaron model not only fits well with the WO3 light absorption curve, but also explains the phenomenon of spectral blue shift in the WO3 evaporation process.
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Scientists have discovered that electrons are injected into the crystal and interact with the surrounding lattice to be localized at a certain lattice position, forming a small polaron that destroys the equilibrium position. Small polarons need to absorb photons when they transit at different lattice positions. This kind of light absorption leads to a transition of a polaron, which is called a Franck-Condon transition. During the transition, the energy of the electronic transition is fully converted into the energy of the photon emission.
