|MLA Citation:||Bloomfield, Louis A. "Question 574"|
How Everything Works 23 Jan 2018. 23 Jan 2018 <http://howeverythingworks.org/print1.php?QNum=574>.
In a typical molecule, the extra energy is released almost immediately, either as light or as the vibrational energy that we associate with heat. But in a few special molecules, this extra energy can become trapped in the molecule. When an electron shifts from one arrangement to another and the total energy of that molecule decreases, the missing energy may leave as a photon of light. But electrons behave as though they were spinning objects and in shifting between arrangements, the electron normally can't change the direction of its spin. In most rearrangements that lead to the emission of light, the electron spins remain unchanged.
However, a glow in the dark molecule is one in which there is an electronically excited state that can only shift to the ground state if one of the electrons changes its direction of spin as the photon of light is being produced. In some molecules, this process is almost totally forbidden by the laws of physics and proceeds so slowly that the molecule may wait for minutes, hours, or even days before it emits the photon and returns to its ground state. When you expose a material containing these molecules to light, its molecules become trapped in these special electronically excited states and they then glow in the dark for a long while afterward.