Photoexcitation is the mechanism of electron excitation by photon absorption, when the energy of the photon is too low to cause photoionization. The absorption of the photon takes place in accordance with Planck's quantum theory.
Photoexcitation plays role in photoisomerization. Photoexcitation is exploited in dye-sensitized solar cells, photochemistry, luminescence, optically pumped lasers, and in some photochromic applications.