The Stern–Volmer relationship, named after
Otto Stern
:''Otto Stern was also the pen name of German women's rights activist Louise Otto-Peters (1819–1895)''.
Otto Stern (; 17 February 1888 – 17 August 1969) was a German-American physicist and Nobel laureate in physics. He was the second most n ...
and
Max Volmer
Max Volmer (; 3 May 1885 – 3 June 1965) was a German physical chemist, who made important contributions in electrochemistry, in particular on electrode kinetics. He co-developed the Butler–Volmer equation. Volmer held the chair and direct ...
, allows the kinetics of a photophysical ''intermolecular'' deactivation process to be explored.
Processes such as
fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, ...
and
phosphorescence
Phosphorescence is a type of photoluminescence related to fluorescence. When exposed to light (radiation) of a shorter wavelength, a phosphorescent substance will glow, absorbing the light and reemitting it at a longer wavelength. Unlike fluo ...
are examples of ''intramolecular'' deactivation (
quenching
In materials science, quenching is the rapid cooling of a workpiece in water, oil, polymer, air, or other fluids to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as ...
) processes. An ''intermolecular'' deactivation is where the presence of another chemical species can accelerate the decay rate of a chemical in its excited state. In general, this process can be represented by a simple equation:
:
or
:
where A is one chemical species, Q is another (known as a quencher) and * designates an excited state.
The kinetics of this process follows the Stern–Volmer relationship:
:
Where
is the intensity, or rate of fluorescence, without a quencher,
is the intensity, or rate of fluorescence, with a quencher,
is the quencher rate coefficient,
is the lifetime of the emissive excited state of A without a quencher present, and