Hi, I have some very basic questions regarding electron energy levels/states. In the basic atom model when an electron becomes excited (i.e. absorbs a photon or collides with a nearby atom or particle) and moves into an energy state greater than its ground state, must it always eventually return to the ground state? Or are there circumstances where an electron may remain in this higher energy state on a permanent basis? Likewise, is it possible for an electron to drop to a lower state (i.e. after emission of a photon) on a permanent basis, or must it always return to its ground state? Any clarification would be very much appreciated.