Erasing the Glow in the Dark: Controlling the Trap and Release of Electrons in Phosphorescent Materials

Common phosphors found in readily available glow-in-the-dark products include transition-metal-doped zinc sulfide and transition-metal-doped strontium aluminate compounds. Phosphorescence of these materials is initiated by light with energies that are specific to each phosphor composition. In many cases, the phosphorescence of these materials can also be darkened by further excitation with light that has lower energy than the minimum energy required to produce the initial glow. The visible darkening of the phosphor material produces an effect akin to an "off switch" or "eraser" for the emitted light. The light excitation to produce the phosphorescence and the darkening can be produced by either coherent or noncoherent light sources with the proper energies and intensities. Phosphor darkening caused by low-energy light can be used in visually remarkable chemistry demonstrations. Additionally, since the distributions of electrons in the low- and high-energy states in these phosphors can be controlled and changed by using various wavelengths of light, they can be used to illustrate concepts associated with steady-state distributions of species and reaction kinetics, as well as applications that utilize controlled release of phosphorescence.