Phosphorescence is a physical phenomenon in which a substance produces luminescence once it has been illuminated with visible light or ultraviolet radiation. Unlike fluorescence, in which the time from absorption to emission is on the order of nanoseconds, in phosphorescence that time can be from microseconds to hours and even days.

We are going to look at a chemical compound called strontium aluminate (SrAl2O4) that has very good phosphorescence properties. This compound is doped with small amounts of europium, dysprosium, cerium, neodymium, manganese or boron.

We will look at various experiments, including a kind of primitive photography with phosphorescent powder. We will also compare it to copper-doped zinc sulfide. The latter is earlier and with a less lasting phosphorescence, although at first the amount of light it emits is striking.

Phosphorescence - Wikipedia: Phosphorescence is a physical phenomenon that involves the emission of light by a material after it has been exposed to light or another form of electromagnetic radiation. Unlike fluorescence, phosphorescence involves a significant delay between absorption and light emission, meaning the light emission persists even after the excitation source has been removed.

Fluorescence - Wikipedia: Fluorescence is a physical phenomenon in which a material absorbs energy in the form of electromagnetic radiation, such as ultraviolet light, and then emits light of longer wavelength, i.e., lower energy, typically visible light. This process occurs instantaneously, unlike phosphorescence.

Strontium aluminate - Wikipedia: Strontium aluminate is a chemical compound with the formula SrAl2O4. It is a material that exhibits phosphorescence and is used in the manufacture of phosphorescent paints and coatings, as well as in the production of luminous objects such as watches and toys.

Zinc sulfide - Wikipedia: Zinc sulfide is a chemical compound with the formula ZnS. It is a semiconductor material that exhibits fluorescence and phosphorescence under certain conditions. It is used in the manufacture of pigments, as a phosphorescent agent in luminous objects, and in optoelectronic devices such as solar cells and light-emitting diodes (LEDs).

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