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Photochemical immersion well reactor (50 mL) with a mercury-vapor lamp.. Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 nm), visible (400–750 nm), or infrared radiation (750–2500 nm).
Laundry detergent fluorescing under ultraviolet light. Optical brighteners, optical brightening agents (OBAs), fluorescent brightening agents (FBAs), or fluorescent whitening agents (FWAs), are chemical compounds that absorb light in the ultraviolet and violet region (usually 340-370 nm) of the electromagnetic spectrum, and re-emit light in the blue region (typically 420-470 nm) through the ...
The incoming light excites a polarization that can be described with the semiconductor Bloch equations. [8] [9] Once the photons are absorbed, electrons and holes are formed with finite momenta in the conduction and valence bands, respectively. The excitations then undergo energy and momentum relaxation towards the band-gap minimum.
Various sources define visible light as narrowly as 420–680 nm [7] [8] to as broadly as 380–800 nm. [9] [10] Under ideal laboratory conditions, people can see infrared up to at least 1,050 nm; [11] children and young adults may perceive ultraviolet wavelengths down to about 310–313 nm. [12] [13] [14]
An example of this phenomenon is when clean air scatters blue light more than red light, and so the midday sky appears blue (apart from the area around the Sun which appears white because the light is not scattered as much). The optical window is also referred to as the "visible window" because it overlaps the human visible response spectrum.
Most photoluminescent events, in which a chemical substrate absorbs and then re-emits a photon of light, are fast, in the order of 10 nanoseconds. Light is absorbed and emitted at these fast time scales in cases where the energy of the photons involved matches the available energy states and allowed transitions of the substrate.
Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by absorption of light or photons. It is defined as the interaction of one or more photons with one target molecule that dissociates into two fragments.
However, the intensity of light drops rapidly with the distance to the light source due to adsorption by the reactants. [12] The influence of the radiation on the reaction rate can often be represented by a power law based on the quantum flow density, i.e. the mole light quantum (previously measured in the unit einstein) per area and time. One ...