Chromism
Encyclopedia
In chemistry
, chromism is a process that induces a change, often reversible, in the color
s of compounds
. In most cases, chromism is based on a change in the electron
states of molecule
s, especially the π- or d-electron state, so this phenomenon is induced by various external stimuli which can alter the electron density of substances. It is known that there are many natural compounds that have chromism, and many artificial compounds with specific chromism have been synthesized to date.
Chromism is classified by what kind of stimuli are used. The major kinds of chromism are as follows.
interacts with material
s in a variety of ways. These can be categorized under the following five headings:
, which is involved. Many of these phenomena are reversible. The following list includes all the classic chromisms plus others of increasing interest in newer outlets.
Commercial applications of color change materials are very common and include photochromics in ophthalmics
, fashion
/cosmetics
and optical memory and optical switch
es, thermochromics in paint
s, plastic
s and textile
s and architecture
, electrochromics in car mirrors
and smart windows
, and solvatochromics in biological probes.
s and pigment
s produce color by the absorption and reflection of light; these are the materials that make a major impact on the color of our daily lives. In 2000, world production of organic
dyes was 800,000 tonnes and of organic pigments, 250,000 tonnes. There is also a very large production of inorganic pigments. Organic dyes are used mainly to color textile fibers
, paper
, hair
, leather
, while pigments are used largely in ink
s, paint
s and plastic
s.
Dyes are also made using the properties of chromic substances:
Photochromic dyes and
Thermochromic dyes
. The exact term used is based on the energy source responsible for the luminescence as in color-change phenomena.
Many of these phenomena are widely used in consumer product
s and other important outlets. Cathodoluminescence
is used in cathode ray tube
s, photoluminescence
in fluorescent lighting and plasma display panels, phosphorescence
in safety signs and low energy lighting, fluorescence
in pigments, inks, optical brightener
s, safety clothing, and biological and medicinal analysis and diagnostics, chemoluminescence
and bioluminescence
in analysis, diagnostics and sensors, and electroluminescence
in the burgeoning areas of light-emitting diode
s (LEDs/OLEDs), displays and panel lighting. Important new developments are taking place in the areas of quantum dots and metallic nanoparticles.
light source, to other molecules in another form of energy, such as thermal or electrical. These laser addressable colorants are used in optical data storage
, organic photoconductors, in photomedicine
(such as photodynamic therapy
of cancer, photodiagnosis and photoinsecticides). The absorption of natural sunlight solar energy by chromophores is exploited in solar cells for the production of electrical energy by inorganic photovoltaics and dye sensitized solar cell (DSSC) and also in the production of useful chemicals via artificial photosynthesis
.
s, by interference and diffraction
as in lustre pigments and holography
, and by modifying the movement of light through materials by electrical means as in organic lasers, or in conjunction with light, opto-electronics, or by purely optical means photonics
for instance by using photonic crystals made by colloidal synthesis and other methods.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
, chromism is a process that induces a change, often reversible, in the color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...
s of compounds
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
. In most cases, chromism is based on a change in the electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
states of molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s, especially the π- or d-electron state, so this phenomenon is induced by various external stimuli which can alter the electron density of substances. It is known that there are many natural compounds that have chromism, and many artificial compounds with specific chromism have been synthesized to date.
Chromism is classified by what kind of stimuli are used. The major kinds of chromism are as follows.
- thermochromismThermochromismThermochromism is the ability of substance to change color due to a change in temperature. A mood ring is an excellent example of this, but it has many other uses such as baby bottles and kettles. Thermochromism is one of several types of chromism.The two basic approaches are based on liquid...
is chromism that is induced by heat, that is, a change of temperature. This is the most common chromism of all. - photochromismPhotochromismPhotochromism is the reversible transformation of a chemical species between two forms by the absorption of electromagnetic radiation, where the two forms have different absorption spectra. Trivially, this can be described as a reversible change of colour upon exposure to light...
is induced by light irradiation. This phenomenon is based on the isomerization between two different molecular structures, light-induced formation of color centers in crystals, precipitation of metal particles in a glass, or other mechanisms. - electrochromismElectrochromismElectrochromism is the phenomenon displayed by some materials of reversibly changing color when a burst of charge is applied. Various types of materials and structures can be used to construct electrochromic devices, depending on the specific applications....
is induced by the gain and loss of electronElectronThe electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s. This phenomenon occurs in compoundsChemical compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with redoxRedoxRedox reactions describe all chemical reactions in which atoms have their oxidation state changed....
active sites, such as metal ionIonAn ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s or organic radicalsRadical (chemistry)Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...
. - solvatochromismSolvatochromismSolvatochromism is the ability of a chemical substance to change color due to a change in solvent polarity. Negative solvatochromism corresponds to hypsochromic shift with increasing solvent polarity and positive solvatochromism corresponds to bathochromic shift with increasing solvent polarity...
depends on the polarityChemical polarityIn chemistry, polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in...
of the solventSolventA solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
. Most solvatochromic compounds are metal complexesComplex (chemistry)In chemistry, a coordination complex or metal complex, is an atom or ion , bonded to a surrounding array of molecules or anions, that are in turn known as ligands or complexing agents...
. - cathodochromism is induced by electron beam irradiation.
Chromic phenomena
Chromic phenomena are those phenomena in which color is produced when lightLight
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
interacts with material
Material
Material is anything made of matter, constituted of one or more substances. Wood, cement, hydrogen, air and water are all examples of materials. Sometimes the term "material" is used more narrowly to refer to substances or components with certain physical properties that are used as inputs to...
s in a variety of ways. These can be categorized under the following five headings:
- Stimulated (reversible) color change
- The absorptionAbsorption (electromagnetic radiation)In physics, absorption of electromagnetic radiation is the way by which the energy of a photon is taken up by matter, typically the electrons of an atom. Thus, the electromagnetic energy is transformed to other forms of energy for example, to heat. The absorption of light during wave propagation is...
and reflectionReflection (physics)Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
of light - The absorption of energy followed by the emission of light
- The absorption of light and energy transfer (or conversion)
- The manipulation of light.
Color changing phenomena
Phenomena which involve the change in color of a chemical compound take their name from the type of external influence, either chemical or physicalPhysics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, which is involved. Many of these phenomena are reversible. The following list includes all the classic chromisms plus others of increasing interest in newer outlets.
- PhotochromismPhotochromismPhotochromism is the reversible transformation of a chemical species between two forms by the absorption of electromagnetic radiation, where the two forms have different absorption spectra. Trivially, this can be described as a reversible change of colour upon exposure to light...
- color change caused by lightLightLight or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
. - ThermochromismThermochromismThermochromism is the ability of substance to change color due to a change in temperature. A mood ring is an excellent example of this, but it has many other uses such as baby bottles and kettles. Thermochromism is one of several types of chromism.The two basic approaches are based on liquid...
- color change caused by heatHeatIn physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
. - ElectrochromismElectrochromismElectrochromism is the phenomenon displayed by some materials of reversibly changing color when a burst of charge is applied. Various types of materials and structures can be used to construct electrochromic devices, depending on the specific applications....
- color change caused by an electrical currentElectricityElectricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
. - GasochromismGasochromismGasochromism is closely related to electrochromism. The process involves the interaction of an electrochrome, usually a metal oxide, such as tungsten oxide, with an oxidizing or reducing gas, commonly oxygen and hydrogen, producing reversible color changes...
- color change caused by a gas - hydrogen/oxygen redoxRedoxRedox reactions describe all chemical reactions in which atoms have their oxidation state changed....
. - SolvatochromismSolvatochromismSolvatochromism is the ability of a chemical substance to change color due to a change in solvent polarity. Negative solvatochromism corresponds to hypsochromic shift with increasing solvent polarity and positive solvatochromism corresponds to bathochromic shift with increasing solvent polarity...
- color change caused by solventSolventA solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
polarityChemical polarityIn chemistry, polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in...
. - VapochromismVapochromismVapochromism strongly overlaps with solvatochromism since vapochromic systems are ones in which dyes change colour in response to the vapour or aroma of an organic compound or gas...
- color change caused by vapour of an organic compound due to chemical polarity/polarisation. - IonochromismIonochromismIonochromic materials, similar to photochromic, thermochromic and other chromic materials, alter colour in the presence of a factor and reverse to their initial state when the factor is removed. The factor which causes colour change in ionochromic substances are ions. A flow of ions through an...
- color change caused by ionIonAn ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s. - HalochromismHalochromismA halochromic material is a material which changes colour when pH changes occur. The term ‘chromic’ is defined as materials that can change colour reversibly with the presence of a factor. In this case, the factor is pH...
- color change caused by a change in pHPHIn chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
. - MechanochromismMechanochromismThe change of colour which occurs when chemicals are put under stress in the solid state by mecahnical grinding, crushing and milling; by friction and rubbing; or in the solid or solution state by high pressure or sonification is covered by the generic term mechanochromism...
- color change caused by mechanical actions. - TribochromismTribochromismTribochromism refers to a change in colour of a material caused by mechanical friction.Tribochromatic materials are used when friction has to be detected. These materials generally change colour under mechanical stress conditions and then the colour gradually fades once the stress is removed....
- color change caused by mechanicalMechanicsMechanics is the branch of physics concerned with the behavior of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment....
frictionFrictionFriction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
. - PiezochromismPiezochromismPiezochromism describes the tendency of certain materials to change color with the application of pressure. This effect is particularly pronounced in plastics.-External links:*...
- color change caused by mechanical pressurePressurePressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
. - Cathodochromism - color change caused by electron beam irradiation.
- Radiochromism - color change caused by ionising radiation.
- Magnetochromism - color change caused by magnetic fieldMagnetic fieldA magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
. - Biochromism - color change caused by interfacing with biological entity.
- Chronochromism - color change indirectly as a result of the passage of timeTimeTime is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....
. - Aggregachromism - color change on dimerisation/aggregation of chromophores.
- Crystallochromism - color change due to changes in crystal structureCrystal structureIn mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
of a chromophore.
Commercial applications of color change materials are very common and include photochromics in ophthalmics
Ophthalmology
Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...
, fashion
Fashion
Fashion, a general term for a currently popular style or practice, especially in clothing, foot wear, or accessories. Fashion references to anything that is the current trend in look and dress up of a person...
/cosmetics
Cosmetics
Cosmetics are substances used to enhance the appearance or odor of the human body. Cosmetics include skin-care creams, lotions, powders, perfumes, lipsticks, fingernail and toe nail polish, eye and facial makeup, towelettes, permanent waves, colored contact lenses, hair colors, hair sprays and...
and optical memory and optical switch
Optical switch
In telecommunication, an optical switch is a switch that enables signals in optical fibers or integrated optical circuits to be selectively switched from one circuit to another....
es, thermochromics in paint
Paint
Paint is any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. One may also consider the digital mimicry thereof...
s, plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
s and textile
Textile
A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...
s and architecture
Architecture
Architecture is both the process and product of planning, designing and construction. Architectural works, in the material form of buildings, are often perceived as cultural and political symbols and as works of art...
, electrochromics in car mirrors
Rear-view mirror
A rear-view mirror is a mirror in automobiles and other vehicles, designed to allow the driver to see rearward through the vehicle's backlight ....
and smart windows
Smart windows
Smart glass, EGlass, or switchable glass, also called smart windows or switchable windows in its application to windows or skylights, refers to electrically switchable glass or glazing which changes light transmission properties when voltage is applied.Certain types of smart glass can allow users...
, and solvatochromics in biological probes.
Dyes and pigments
Classical dyeDye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
s and pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
s produce color by the absorption and reflection of light; these are the materials that make a major impact on the color of our daily lives. In 2000, world production of organic
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
dyes was 800,000 tonnes and of organic pigments, 250,000 tonnes. There is also a very large production of inorganic pigments. Organic dyes are used mainly to color textile fibers
Textile
A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...
, paper
Paper
Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
, hair
Hair
Hair is a filamentous biomaterial, that grows from follicles found in the dermis. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class....
, leather
Leather
Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...
, while pigments are used largely in ink
Ink
Ink is a liquid or paste that contains pigments and/or dyes and is used to color a surface to produce an image, text, or design. Ink is used for drawing and/or writing with a pen, brush, or quill...
s, paint
Paint
Paint is any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. One may also consider the digital mimicry thereof...
s and plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
s.
Dyes are also made using the properties of chromic substances:
Photochromic dyes and
Thermochromic dyes
Luminescence
The absorption of energy followed by the emission of light is often described by the term luminescenceLuminescence
Luminescence is emission of light by a substance not resulting from heat; it is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a...
. The exact term used is based on the energy source responsible for the luminescence as in color-change phenomena.
- Electrical - electroluminescenceElectroluminescenceElectroluminescence is an optical phenomenon and electrical phenomenon in which a material emits light in response to the passage of an electric current or to a strong electric field...
GalvanoluminescenceGalvanoluminescenceGalvanoluminescence Is the emission of light produced by the passage of an electrical current through an appropriate electrolyte in which an electrode, made of certain metals such as aluminium or tantalum, has been immersed. An example being the electrolysis of sodium bromide ....
SonoluminescenceSonoluminescenceSonoluminescence is the emission of short bursts of light from imploding bubbles in a liquid when excited by sound.-History:The effect was first discovered at the University of Cologne in 1934 as a result of work on sonar. H. Frenzel and H. Schultes put an ultrasound transducer in a tank of...
. - Photons (light) - PhotoluminescencePhotoluminescencePhotoluminescence is a process in which a substance absorbs photons and then re-radiates photons. Quantum mechanically, this can be described as an excitation to a higher energy state and then a return to a lower energy state accompanied by the emission of a photon...
FluorescenceFluorescenceFluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
PhosphorescencePhosphorescencePhosphorescence 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...
Biofluorescence. - Chemical - Chemiluminescence BioluminescenceBioluminescenceBioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...
ElectrochemiluminescenceElectrochemiluminescenceElectrochemiluminescence or electrogenerated chemiluminescence is a kind of luminescence produced during electrochemical reactions in solutions. In electrogenerated chemiluminescence, electrochemically generated intermediates undergo a highly exergonic reaction to produce an electronically excited...
. - ThermalThermalA thermal column is a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and are an example of convection. The sun warms the ground, which in turn warms the air directly above it...
- ThermoluminescenceThermoluminescenceThermoluminescence is a form of luminescence that is exhibited by certain crystalline materials, such as some minerals, when previously absorbed energy from electromagnetic radiation or other ionizing radiation is re-emitted as light upon heating of the material...
Pyroluminescence Candololuminescence. - Electron Beam - CathodoluminescenceCathodoluminescenceCathodoluminescence is an optical and electrical phenomenon whereby a beam of electrons is generated by an electron gun and then impacts on a luminescent material such as a phosphor, causing the material to emit visible light. The most common example is the screen of a television...
Anodoluminescence RadioluminescenceRadioluminescenceRadioluminescence is the phenomenon by which luminescence is produced in a material by the bombardment of ionizing radiation such as beta particles.-Tritium:...
. - MechanicalMechanicsMechanics is the branch of physics concerned with the behavior of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment....
- TriboluminescenceTriboluminescenceTriboluminescence is an optical phenomenon in which light is generated when material is pulled apart, ripped, scratched, crushed, or rubbed through the breaking of chemical bonds in the material. The phenomenon is not fully understood, but appears to be caused by the separation and reunification...
Fractoluminescence MechanoluminescenceMechanoluminescenceMechanoluminescence is light emission resulting from any mechanical action on a solid. It can be produced through ultrasound, or through other means.* Fractoluminescence is caused by stress that results in the formation of fractures....
CrystalloluminescenceCrystalloluminescenceCrystalloluminescence is the effect of luminescence produced during crystallization.The abstract of an article by B. P. Chandra, V. Kalia and S. C. Datt of Rani Durgavati University , entitled Crystalloluminescence: a new tool to determine the critical size of a crystal nucleus, states:-Sources:*...
LyoluminescenceLyoluminescenceLyoluminescence refers to the emission of light while dissolving a solid into a liquid solvent. It is actually a form of chemoluminescence. The most common lyoluminescent effect is seen when solid samples which have been heavily irradiated by ionizing radiation are dissolved in water...
Elasticoluminescence.
Many of these phenomena are widely used in consumer product
Consumer product
A consumer product is generally any tangible personal property for sale and that is used for personal, family, or household for non-business purposes. The determination whether a good is a consumer product requires a factual finding, on a case-by-case basis...
s and other important outlets. Cathodoluminescence
Cathodoluminescence
Cathodoluminescence is an optical and electrical phenomenon whereby a beam of electrons is generated by an electron gun and then impacts on a luminescent material such as a phosphor, causing the material to emit visible light. The most common example is the screen of a television...
is used in cathode ray tube
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
s, photoluminescence
Photoluminescence
Photoluminescence is a process in which a substance absorbs photons and then re-radiates photons. Quantum mechanically, this can be described as an excitation to a higher energy state and then a return to a lower energy state accompanied by the emission of a photon...
in fluorescent lighting and plasma display panels, phosphorescence
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...
in safety signs and low energy lighting, fluorescence
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
in pigments, inks, optical brightener
Optical brightener
Optical brighteners, optical brightening agents , fluorescent brightening agents or fluorescent whitening agents are dyes that absorb light in the ultraviolet and violet region of the electromagnetic spectrum, and re-emit light in the blue region...
s, safety clothing, and biological and medicinal analysis and diagnostics, chemoluminescence
Chemoluminescence
Chemiluminescence is the emission of light with limited emission of heat , as the result of a chemical reaction...
and bioluminescence
Bioluminescence
Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...
in analysis, diagnostics and sensors, and electroluminescence
Electroluminescence
Electroluminescence is an optical phenomenon and electrical phenomenon in which a material emits light in response to the passage of an electric current or to a strong electric field...
in the burgeoning areas of light-emitting diode
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...
s (LEDs/OLEDs), displays and panel lighting. Important new developments are taking place in the areas of quantum dots and metallic nanoparticles.
Light and energy transfer
Absorption of light and energy transfer (or conversion) involves colored molecules that can transfer electromagnetic energy, usually from a laserLaser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
light source, to other molecules in another form of energy, such as thermal or electrical. These laser addressable colorants are used in optical data storage
Optical disc
In computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data in the form of pits and lands on a special material on one of its flat surfaces...
, organic photoconductors, in photomedicine
Photomedicine
Photomedicine is an interdisciplinary branch of medicine that involves the study and application of light with respect to health and disease. Photomedicine may be related to the practice of various fields of medicine including dermatology, surgery, interventional radiology, optical diagnostics,...
(such as photodynamic therapy
Photodynamic therapy
Photodynamic therapy is used clinically to treat a wide range of medical conditions, including malignant cancers, and is recognised as a treatment strategy which is both minimally invasive and minimally toxic...
of cancer, photodiagnosis and photoinsecticides). The absorption of natural sunlight solar energy by chromophores is exploited in solar cells for the production of electrical energy by inorganic photovoltaics and dye sensitized solar cell (DSSC) and also in the production of useful chemicals via artificial photosynthesis
Artificial photosynthesis
Artificial photosynthesis is a chemical process that replicates the natural process of photosynthesis, a process that converts sunlight, water, and carbon dioxide into carbohydrates and oxygen. The term is commonly used to refer to any scheme for capturing and storing the energy from sunlight in...
.
Light manipulation
Materials may be used to manipulate light via a variety of mechanisms. For instance, a change of orientation of molecules as in liquid crystal displayLiquid crystal display
A liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....
s, by interference and diffraction
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
as in lustre pigments and holography
Holography
Holography is a technique that allows the light scattered from an object to be recorded and later reconstructed so that when an imaging system is placed in the reconstructed beam, an image of the object will be seen even when the object is no longer present...
, and by modifying the movement of light through materials by electrical means as in organic lasers, or in conjunction with light, opto-electronics, or by purely optical means photonics
Photonics
The science of photonics includes the generation, emission, transmission, modulation, signal processing, switching, amplification, detection and sensing of light. The term photonics thereby emphasizes that photons are neither particles nor waves — they are different in that they have both particle...
for instance by using photonic crystals made by colloidal synthesis and other methods.