I seem to have some trouble finding a definite answer by searching the following: It is my understanding that when an electron is excited to a higher energy state, it will spontaneously decay back and emit a photon. My questions are: Is the wavelength of light required to excite an electron going to be the same wavelength given off as it decays back? Sort of like a particular freq. for a particular jump going either way? Also, is light the only type of energy that can cause an electron to reach an excited state, it seems that maybe one could be "forced" out simply by a collision or even a bond forming/breaking. I apologize for being such a lay person here in this section, but I was never taught this in school, and am trying to educate myself. Any help would be greatly appreciated.