Many things have glow in the dark properties (glow sticks, paint, toys ..), and I am wondering what is the physics behind them. How do these materials store light energy and emit it later when dark?
What dictates the wavelength(s) of the glow? Is there a limit on how much energy can be stored and recovered in these materials? Do they give out heat as well as light?
Best Answer
This phenomenon is called phosphorescence. Electrons in the material are pushed into excited states by light, and then drop back down, emitting light with a characteristic frequency corresponding to the energy of the transition. It is analogous to fluorescence, however whereas fluorescence is a very rapid process, phosphorescence is delayed due to the electronic transition involved being 'forbidden' (in practice, this means low-probability at non-zero temperatures). As such, the process of all of the atoms or molecules in the material returning to their ground state is a drawn out over minutes or hours.
Note: Glow sticks are a different matter - they employ an organic fluorescent dye and an oxidising agent.
Summary:
Wavelength: determined by the energy of the electronic transition.
Energy limit: You will eventually reach a point of saturation where the material is totally excited.
Heat emission: probably.