"Excitation energy" refers to the energy required to excite or energize something. It is the energy needed to move an object or system from a lower energy state to a higher energy state. Full definition
Kamaratos, E., 1984: Covalent bonding effect on the mean excitation energy of H2 with the local plasma model. (pubs.giss.nasa.gov)
If the polymers are then exposed to a laser beam, they absorb the light and store it as excitation energy. (sciencedaily.com)
Using this method, we were able to determine the colour of the emitted light and finally the extension of excitation energy over the chain - like polymers,» explained Dr. Richard Hildner, who coordinated the research at the University of Bayreuth. (sciencedaily.com)