Fluorescence Phosphorscence:

Fluorescence is the emission of electromagnetic radiation light by a substance that has absorbed radiation of a different wavelength. However, under conditions in which intense radiation is being absorbed, it is possible for one electron to absorb two photons (multiple photon absorption), which can lead to the emission of radiation having a smaller wavelength than the excitation source. The energy difference between the absorbed and emitted photons is due to thermal losses.

Dissipation of vibrational energy occurs on a much greater time scale than fluorescent emission. The most striking examples of this phenomenon occur when the absorbed photon is in the ultraviolet region of the spectrum, and is thus invisible, and the emitted light is in the visible region. Practical applications of this effect are found in mineralogy, gemology, chemical sensors, fluorescent labelling, dyes, biological detectors etc.

Molecules that are excited through light absorption or via a different process (e.g. as the product of a reaction) can transfer energy to a second 'sensitized' molecule, which is converted to its excited state and can then fluoresce. This process is used in lightsticks to produce different colors.

Fluorescence in the life sciences is used generally as a non-destructive way of tracking or analysis biological molecules by means of the fluorescent emission at a specific frequency where there is no background from the excitation light, as relatively few cellular components are naturally fluorescent (called intrinsic or autofluorescence). In fact, a protein or other component can be "labelled" with a extrinsic fluorophore, a fluorescent dye which can be a small molecule, protein or quantum dot, finding a large use in many biological applications.

Phosphorescence

Phosphorescence is a specific type of photoluminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs. The slower time scales of the re-emission are associated with "forbidden" energy state transitions in quantum mechanics. As these transitions occur less often in certain materials, absorbed radiation may be re-emitted at a lower intensity for up to several hours.

The study of phosphorescent materials led to the discovery of radioactivity in 1896.

Some examples of "glow-in-the-dark" materials do not glow because they are phosphorescent.

For example, "glow sticks" glow due to a chemiluminescent process which is commonly mistaken for phosphorescence. In chemiluminescence, an excited state is created via a chemical reaction. The light emission tracks the kinetic progress of the underlying chemical reaction. The excited state will then transfer to a "dye" molecule, also known as a sensitizer or fluorophor, and subsequently fluoresce back to the ground state.