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Photoelectrochemical process

Photoelectrochemical processes are processes in photoelectrochemistry; they usually involve transforming light into other forms of energy.[1] These processes apply to photochemistry, optically pumped lasers, sensitized solar cells, luminescence, and photochromism.

Electron excitation edit

 
After absorbing energy, an electron may jump from the ground state to a higher energy excited state.

Electron excitation is the movement of an electron to a higher energy state. This can either be done by photoexcitation (PE), where the original electron absorbs the photon and gains all the photon's energy or by electrical excitation (EE), where the original electron absorbs the energy of another, energetic electron. Within a semiconductor crystal lattice, thermal excitation is a process where lattice vibrations provide enough energy to move electrons to a higher energy band. When an excited electron falls back to a lower energy state again, it is called electron relaxation. This can be done by radiation of a photon or giving the energy to a third spectator particle as well.[2]

In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state. The excited state, in general, is in relation to the ground state, where the excited state is at a higher energy level than the ground state.

Photoexcitation edit

Photoexcitation is the mechanism of electron excitation by photon absorption, when the energy of the photon is too low to cause photoionization. The absorption of the photon takes place in accordance with Planck's quantum theory.

Photoexcitation plays role in photoisomerization. Photoexcitation is exploited in dye-sensitized solar cells, photochemistry, luminescence, optically pumped lasers, and in some photochromic applications.

 
Military laser experiment

Photoisomerization edit

 
Photoisomerization of azobenzene

In chemistry, photoisomerization is molecular behavior in which structural change between isomers is caused by photoexcitation. Both reversible and irreversible photoisomerization reactions exist. However, the word "photoisomerization" usually indicates a reversible process. Photoisomerizable molecules are already put to practical use, for instance, in pigments for rewritable CDs, DVDs, and 3D optical data storage solutions. In addition, recent interest in photoisomerizable molecules has been aimed at molecular devices, such as molecular switches,[3] molecular motors,[4] and molecular electronics.

Photoisomerization behavior can be roughly categorized into several classes. Two major classes are trans-cis (or 'E-'Z) conversion, and open-closed ring transition. Examples of the former include stilbene and azobenzene. This type of compounds has a double bond, and rotation or inversion around the double bond affords isomerization between the two states. Examples of the latter include fulgide and diarylethene. This type of compounds undergoes bond cleavage and bond creation upon irradiation with particular wavelengths of light. Still another class is the di-π-methane rearrangement.

Photoionization edit

Photoionization is the physical process in which an incident photon ejects one or more electrons from an atom, ion or molecule. This is essentially the same process that occurs with the photoelectric effect with metals. In the case of a gas or single atoms, the term photoionization is more common.[5]

The ejected electrons, known as photoelectrons, carry information about their pre-ionized states. For example, a single electron can have a kinetic energy equal to the energy of the incident photon minus the electron binding energy of the state it left. Photons with energies less than the electron binding energy may be absorbed or scattered but will not photoionize the atom or ion.[5]

For example, to ionize hydrogen, photons need an energy greater than 13.6 electronvolts (the Rydberg energy), which corresponds to a wavelength of 91.2 nm.[6] For photons with greater energy than this, the energy of the emitted photoelectron is given by:

 

where h is the Planck constant and ν is the frequency of the photon.

This formula defines the photoelectric effect.

Not every photon which encounters an atom or ion will photoionize it. The probability of photoionization is related to the photoionization cross-section, which depends on the energy of the photon and the target being considered. For photon energies below the ionization threshold, the photoionization cross-section is near zero. But with the development of pulsed lasers it has become possible to create extremely intense, coherent light where multi-photon ionization may occur. At even higher intensities (around 1015 - 1016 W/cm2 of infrared or visible light), non-perturbative phenomena such as barrier suppression ionization[7] and rescattering ionization[8] are observed.

Multi-photon ionization edit

Several photons of energy below the ionization threshold may actually combine their energies to ionize an atom. This probability decreases rapidly with the number of photons required, but the development of very intense, pulsed lasers still makes it possible. In the perturbative regime (below about 1014 W/cm2 at optical frequencies), the probability of absorbing N photons depends on the laser-light intensity I as IN .[9]

Above threshold ionization (ATI) [10] is an extension of multi-photon ionization where even more photons are absorbed than actually would be necessary to ionize the atom. The excess energy gives the released electron higher kinetic energy than the usual case of just-above threshold ionization. More precisely, the system will have multiple peaks in its photoelectron spectrum which are separated by the photon energies, this indicates that the emitted electron has more kinetic energy than in the normal (lowest possible number of photons) ionization case. The electrons released from the target will have approximately an integer number of photon-energies more kinetic energy. In intensity regions between 1014 W/cm2 and 1018 W/cm2, each of MPI, ATI, and barrier suppression ionization can occur simultaneously, each contributing to the overall ionization of the atoms involved.[11]

Photo-Dember edit

In semiconductor physics the Photo-Dember effect (named after its discoverer H. Dember) consists in the formation of a charge dipole in the vicinity of a semiconductor surface after ultra-fast photo-generation of charge carriers. The dipole forms owing to the difference of mobilities (or diffusion constants) for holes and electrons which combined with the break of symmetry provided by the surface lead to an effective charge separation in the direction perpendicular to the surface.[12]

Grotthuss–Draper law edit

The Grotthuss–Draper law (also called the principle of photochemical activation) states that only that light which is absorbed by a system can bring about a photochemical change. Materials such as dyes and phosphors must be able to absorb "light" at optical frequencies. This law provides a basis for fluorescence and phosphorescence. The law was first proposed in 1817 by Theodor Grotthuss and in 1842, independently, by John William Draper.[5]

This is considered to be one of the two basic laws of photochemistry. The second law is the Stark–Einstein law, which says that primary chemical or physical reactions occur with each photon absorbed.[5]

Stark–Einstein law edit

The Stark–Einstein law is named after German-born physicists Johannes Stark and Albert Einstein, who independently formulated the law between 1908 and 1913. It is also known as the photochemical equivalence law or photoequivalence law. In essence it says that every photon that is absorbed will cause a (primary) chemical or physical reaction.[13]

The photon is a quantum of radiation, or one unit of radiation. Therefore, this is a single unit of EM radiation that is equal to the Planck constant (h) times the frequency of light. This quantity is symbolized by γ, , or ħω.

The photochemical equivalence law is also restated as follows: for every mole of a substance that reacts, an equivalent mole of quanta of light are absorbed. The formula is:[13]

 

where NA is the Avogadro constant.

The photochemical equivalence law applies to the part of a light-induced reaction that is referred to as the primary process (i.e. absorption or fluorescence).[13]

In most photochemical reactions the primary process is usually followed by so-called secondary photochemical processes that are normal interactions between reactants not requiring absorption of light. As a result, such reactions do not appear to obey the one quantum–one molecule reactant relationship.[13]

The law is further restricted to conventional photochemical processes using light sources with moderate intensities; high-intensity light sources such as those used in flash photolysis and in laser experiments are known to cause so-called biphotonic processes; i.e., the absorption by a molecule of a substance of two photons of light.[13]

Absorption edit

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 often called attenuation. Usually, the absorption of waves does not depend on their intensity (linear absorption), although in certain conditions (usually, in optics), the medium changes its transparency dependently on the intensity of waves going through, and the Saturable absorption (or nonlinear absorption) occurs.

Photosensitization edit

Photosensitization is a process of transferring the energy of absorbed light. After absorption, the energy is transferred to the (chosen) reactants. This is part of the work of photochemistry in general. In particular this process is commonly employed where reactions require light sources of certain wavelengths that are not readily available.[14]

For example, mercury absorbs radiation at 1849 and 2537 angstroms, and the source is often high-intensity mercury lamps. It is a commonly used sensitizer. When mercury vapor is mixed with ethylene, and the compound is irradiated with a mercury lamp, this results in the photodecomposition of ethylene to acetylene. This occurs on absorption of light to yield excited state mercury atoms, which are able to transfer this energy to the ethylene molecules, and are in turn deactivated to their initial energy state.[14]

Cadmium; some of the noble gases, for example xenon; zinc; benzophenone; and a large number of organic dyes, are also used as sensitizers.[14]

Photosensitisers are a key component of photodynamic therapy used to treat cancers.

Sensitizer edit

A sensitizer in chemiluminescence is a chemical compound, capable of light emission after it has received energy from a molecule, which became excited previously in the chemical reaction. A good example is this:

When an alkaline solution of sodium hypochlorite and a concentrated solution of hydrogen peroxide are mixed, a reaction occurs:

ClO(aq) + H2O2(aq) → O2*(g) + H+(aq) + Cl(aq) + OH(aq)

O2*is excited oxygen – meaning, one or more electrons in the O2 molecule have been promoted to higher-energy molecular orbitals. Hence, oxygen produced by this chemical reaction somehow 'absorbed' the energy released by the reaction and became excited. This energy state is unstable, therefore it will return to the ground state by lowering its energy. It can do that in more than one way:

  • it can react further, without any light emission
  • it can lose energy without emission, for example, giving off heat to the surroundings or transferring energy to another molecule
  • it can emit light

The intensity, duration and color of emitted light depend on quantum and kinetical factors. However, excited molecules are frequently less capable of light emission in terms of brightness and duration when compared to sensitizers. This is because sensitizers can store energy (that is, be excited) for longer periods of time than other excited molecules. The energy is stored through means of quantum vibration, so sensitizers are usually compounds which either include systems of aromatic rings or many conjugated double and triple bonds in their structure. Hence, if an excited molecule transfers its energy to a sensitizer thus exciting it, longer and easier to quantify light emission is often observed.

The color (that is, the wavelength), brightness and duration of emission depend upon the sensitizer used. Usually, for a certain chemical reaction, many different sensitizers can be used.

List of some common sensitizers edit

Fluorescence spectroscopy edit

Fluorescence spectroscopy aka fluorometry or spectrofluorometry, is a type of electromagnetic spectroscopy which analyzes fluorescence from a sample. It involves using a beam of light, usually ultraviolet light, that excites the electrons in molecules of certain compounds and causes them to emit light of a lower energy, typically, but not necessarily, visible light. A complementary technique is absorption spectroscopy.[15][16]

Devices that measure fluorescence are called fluorometers or fluorimeters.

Absorption spectroscopy edit

Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating field. The intensity of the absorption varies as a function of frequency, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum.[15][16]

See also edit

References edit

  1. ^ Gerischer, Heinz (1985). "Semiconductor electrodes and their interaction with light". In Schiavello, Mario (ed.). Photoelectrochemistry, Photocatalysis and Photoreactors Fundamentals and Developments. Springer. p. 39. ISBN 978-90-277-1946-1.
  2. ^ Madden, R. P.; Codling, K. (1965). "Two electron states in Helium". Astrophysical Journal. 141: 364. Bibcode:1965ApJ...141..364M. doi:10.1086/148132.
  3. ^ Mammana, A.; et al. (2011). "A Chiroptical Photoswitchable DNA Complex" (PDF). Journal of Physical Chemistry B. 115 (40): 11581–11587. doi:10.1021/jp205893y. PMID 21879715. S2CID 33375716.
  4. ^ Vachon, J.; et al. (2014). "An ultrafast surface-bound photo-active molecular motor". Photochemical and Photobiological Sciences. 13 (2): 241–246. doi:10.1039/C3PP50208B. PMID 24096390. S2CID 23165784.
  5. ^ a b c d "Radiation". Encyclopædia Britannica Online. Retrieved 9 November 2009.
  6. ^ Carroll, B. W.; Ostlie, D. A. (2007). An Introduction to Modern Astrophysics. Addison-Wesley. p. 121. ISBN 978-0-321-44284-0.
  7. ^ Delone, N. B.; Krainov, V. P. (1998). "Tunneling and barrier-suppression ionization of atoms and ions in a laser radiation field". Physics-Uspekhi. 41 (5): 469–485. Bibcode:1998PhyU...41..469D. doi:10.1070/PU1998v041n05ABEH000393. S2CID 250763981.
  8. ^ Dichiara, A.; et al. (2005). "Cross-shell multielectron ionization of xenon by an ultrastrong laser field". Proceedings of the Quantum Electronics and Laser Science Conference. Vol. 3. Optical Society of America. pp. 1974–1976. doi:10.1109/QELS.2005.1549346. ISBN 1-55752-796-2.
  9. ^ Deng, Z.; Eberly, J. H. (1985). "Multiphoton absorption above ionization threshold by atoms in strong laser fields". Journal of the Optical Society of America B. 2 (3): 491. Bibcode:1985JOSAB...2..486D. doi:10.1364/JOSAB.2.000486.
  10. ^ Agostini, P.; et al. (1979). "Free-Free Transitions Following Six-Photon Ionization of Xenon Atoms". Physical Review Letters. 42 (17): 1127–1130. Bibcode:1979PhRvL..42.1127A. doi:10.1103/PhysRevLett.42.1127.
  11. ^ Nandor, M.; et al. (1999). "Detailed comparison of above-threshold-ionization spectra from accurate numerical integrations and high-resolution measurements". Physical Review A. 60 (3): 1771–1774. Bibcode:1999PhRvA..60.1771N. doi:10.1103/PhysRevA.60.R1771.
  12. ^ Dekorsy, T.; et al. (1996). "THz electromagnetic emission by coherent infrared-active phonons" (PDF). Physical Review B. 53 (7): 4005–4014. Bibcode:1996PhRvB..53.4005D. doi:10.1103/PhysRevB.53.4005. PMID 9983955.
  13. ^ a b c d e "Photochemical equivalence law". Encyclopædia Britannica Online. Retrieved 7 November 2009.
  14. ^ a b c "Photosensitization". Encyclopædia Britannica Online. Retrieved 10 November 2009.
  15. ^ a b Hollas, J. M. (2004). Modern Spectroscopy (4th ed.). John Wiley & Sons. ISBN 978-0-470-84416-8.
  16. ^ a b Harris, D. C.; Bertolucci, M. D. (1978). Symmetry and Spectroscopy: An introduction to vibrational and electronic spectroscopy (Reprint ed.). Dover Publications. ISBN 978-0-486-66144-5.


photoelectrochemical, process, processes, photoelectrochemistry, they, usually, involve, transforming, light, into, other, forms, energy, these, processes, apply, photochemistry, optically, pumped, lasers, sensitized, solar, cells, luminescence, photochromism,. Photoelectrochemical processes are processes in photoelectrochemistry they usually involve transforming light into other forms of energy 1 These processes apply to photochemistry optically pumped lasers sensitized solar cells luminescence and photochromism Contents 1 Electron excitation 2 Photoexcitation 3 Photoisomerization 4 Photoionization 4 1 Multi photon ionization 5 Photo Dember 6 Grotthuss Draper law 7 Stark Einstein law 8 Absorption 9 Photosensitization 10 Sensitizer 10 1 List of some common sensitizers 11 Fluorescence spectroscopy 12 Absorption spectroscopy 13 See also 14 ReferencesElectron excitation edit nbsp After absorbing energy an electron may jump from the ground state to a higher energy excited state Electron excitation is the movement of an electron to a higher energy state This can either be done by photoexcitation PE where the original electron absorbs the photon and gains all the photon s energy or by electrical excitation EE where the original electron absorbs the energy of another energetic electron Within a semiconductor crystal lattice thermal excitation is a process where lattice vibrations provide enough energy to move electrons to a higher energy band When an excited electron falls back to a lower energy state again it is called electron relaxation This can be done by radiation of a photon or giving the energy to a third spectator particle as well 2 In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state The excited state in general is in relation to the ground state where the excited state is at a higher energy level than the ground state Photoexcitation editSee also Photoelectric effect Photoexcitation is the mechanism of electron excitation by photon absorption when the energy of the photon is too low to cause photoionization The absorption of the photon takes place in accordance with Planck s quantum theory Photoexcitation plays role in photoisomerization Photoexcitation is exploited in dye sensitized solar cells photochemistry luminescence optically pumped lasers and in some photochromic applications nbsp Military laser experimentPhotoisomerization edit nbsp Photoisomerization of azobenzeneIn chemistry photoisomerization is molecular behavior in which structural change between isomers is caused by photoexcitation Both reversible and irreversible photoisomerization reactions exist However the word photoisomerization usually indicates a reversible process Photoisomerizable molecules are already put to practical use for instance in pigments for rewritable CDs DVDs and 3D optical data storage solutions In addition recent interest in photoisomerizable molecules has been aimed at molecular devices such as molecular switches 3 molecular motors 4 and molecular electronics Photoisomerization behavior can be roughly categorized into several classes Two major classes are trans cis or E Z conversion and open closed ring transition Examples of the former include stilbene and azobenzene This type of compounds has a double bond and rotation or inversion around the double bond affords isomerization between the two states Examples of the latter include fulgide and diarylethene This type of compounds undergoes bond cleavage and bond creation upon irradiation with particular wavelengths of light Still another class is the di p methane rearrangement Photoionization editSee also Ultraviolet photoelectron spectroscopy Photoionization is the physical process in which an incident photon ejects one or more electrons from an atom ion or molecule This is essentially the same process that occurs with the photoelectric effect with metals In the case of a gas or single atoms the term photoionization is more common 5 The ejected electrons known as photoelectrons carry information about their pre ionized states For example a single electron can have a kinetic energy equal to the energy of the incident photon minus the electron binding energy of the state it left Photons with energies less than the electron binding energy may be absorbed or scattered but will not photoionize the atom or ion 5 For example to ionize hydrogen photons need an energy greater than 13 6 electronvolts the Rydberg energy which corresponds to a wavelength of 91 2 nm 6 For photons with greater energy than this the energy of the emitted photoelectron is given by m v 2 2 h n 13 6 e V displaystyle mv 2 over 2 h nu 13 6eV nbsp where h is the Planck constant and n is the frequency of the photon This formula defines the photoelectric effect Not every photon which encounters an atom or ion will photoionize it The probability of photoionization is related to the photoionization cross section which depends on the energy of the photon and the target being considered For photon energies below the ionization threshold the photoionization cross section is near zero But with the development of pulsed lasers it has become possible to create extremely intense coherent light where multi photon ionization may occur At even higher intensities around 1015 1016 W cm2 of infrared or visible light non perturbative phenomena such as barrier suppression ionization 7 and rescattering ionization 8 are observed Multi photon ionization edit See also Fluorescence spectroscopy Fluorescence and Photoionization mode Several photons of energy below the ionization threshold may actually combine their energies to ionize an atom This probability decreases rapidly with the number of photons required but the development of very intense pulsed lasers still makes it possible In the perturbative regime below about 1014 W cm2 at optical frequencies the probability of absorbing N photons depends on the laser light intensity I as IN 9 Above threshold ionization ATI 10 is an extension of multi photon ionization where even more photons are absorbed than actually would be necessary to ionize the atom The excess energy gives the released electron higher kinetic energy than the usual case of just above threshold ionization More precisely the system will have multiple peaks in its photoelectron spectrum which are separated by the photon energies this indicates that the emitted electron has more kinetic energy than in the normal lowest possible number of photons ionization case The electrons released from the target will have approximately an integer number of photon energies more kinetic energy In intensity regions between 1014 W cm2 and 1018 W cm2 each of MPI ATI and barrier suppression ionization can occur simultaneously each contributing to the overall ionization of the atoms involved 11 Photo Dember editMain article Photo Dember In semiconductor physics the Photo Dember effect named after its discoverer H Dember consists in the formation of a charge dipole in the vicinity of a semiconductor surface after ultra fast photo generation of charge carriers The dipole forms owing to the difference of mobilities or diffusion constants for holes and electrons which combined with the break of symmetry provided by the surface lead to an effective charge separation in the direction perpendicular to the surface 12 Grotthuss Draper law editThe Grotthuss Draper law also called the principle of photochemical activation states that only that light which is absorbed by a system can bring about a photochemical change Materials such as dyes and phosphors must be able to absorb light at optical frequencies This law provides a basis for fluorescence and phosphorescence The law was first proposed in 1817 by Theodor Grotthuss and in 1842 independently by John William Draper 5 This is considered to be one of the two basic laws of photochemistry The second law is the Stark Einstein law which says that primary chemical or physical reactions occur with each photon absorbed 5 Stark Einstein law editThe Stark Einstein law is named after German born physicists Johannes Stark and Albert Einstein who independently formulated the law between 1908 and 1913 It is also known as the photochemical equivalence law or photoequivalence law In essence it says that every photon that is absorbed will cause a primary chemical or physical reaction 13 The photon is a quantum of radiation or one unit of radiation Therefore this is a single unit of EM radiation that is equal to the Planck constant h times the frequency of light This quantity is symbolized by g hn or ħw The photochemical equivalence law is also restated as follows for every mole of a substance that reacts an equivalent mole of quanta of light are absorbed The formula is 13 D E mol N A h n displaystyle Delta E text mol N text A h nu nbsp where NA is the Avogadro constant The photochemical equivalence law applies to the part of a light induced reaction that is referred to as the primary process i e absorption or fluorescence 13 In most photochemical reactions the primary process is usually followed by so called secondary photochemical processes that are normal interactions between reactants not requiring absorption of light As a result such reactions do not appear to obey the one quantum one molecule reactant relationship 13 The law is further restricted to conventional photochemical processes using light sources with moderate intensities high intensity light sources such as those used in flash photolysis and in laser experiments are known to cause so called biphotonic processes i e the absorption by a molecule of a substance of two photons of light 13 Absorption editMain article Absorption 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 often called attenuation Usually the absorption of waves does not depend on their intensity linear absorption although in certain conditions usually in optics the medium changes its transparency dependently on the intensity of waves going through and the Saturable absorption or nonlinear absorption occurs Photosensitization editPhotosensitization is a process of transferring the energy of absorbed light After absorption the energy is transferred to the chosen reactants This is part of the work of photochemistry in general In particular this process is commonly employed where reactions require light sources of certain wavelengths that are not readily available 14 For example mercury absorbs radiation at 1849 and 2537 angstroms and the source is often high intensity mercury lamps It is a commonly used sensitizer When mercury vapor is mixed with ethylene and the compound is irradiated with a mercury lamp this results in the photodecomposition of ethylene to acetylene This occurs on absorption of light to yield excited state mercury atoms which are able to transfer this energy to the ethylene molecules and are in turn deactivated to their initial energy state 14 Cadmium some of the noble gases for example xenon zinc benzophenone and a large number of organic dyes are also used as sensitizers 14 Photosensitisers are a key component of photodynamic therapy used to treat cancers Sensitizer editFor the particulate material used to create voids that aid in the initiation or propagation of an explosive s detonation wave see Explosive sensitiser A sensitizer in chemiluminescence is a chemical compound capable of light emission after it has received energy from a molecule which became excited previously in the chemical reaction A good example is this When an alkaline solution of sodium hypochlorite and a concentrated solution of hydrogen peroxide are mixed a reaction occurs ClO aq H2O2 aq O2 g H aq Cl aq OH aq O2 is excited oxygen meaning one or more electrons in the O2 molecule have been promoted to higher energy molecular orbitals Hence oxygen produced by this chemical reaction somehow absorbed the energy released by the reaction and became excited This energy state is unstable therefore it will return to the ground state by lowering its energy It can do that in more than one way it can react further without any light emission it can lose energy without emission for example giving off heat to the surroundings or transferring energy to another molecule it can emit lightThe intensity duration and color of emitted light depend on quantum and kinetical factors However excited molecules are frequently less capable of light emission in terms of brightness and duration when compared to sensitizers This is because sensitizers can store energy that is be excited for longer periods of time than other excited molecules The energy is stored through means of quantum vibration so sensitizers are usually compounds which either include systems of aromatic rings or many conjugated double and triple bonds in their structure Hence if an excited molecule transfers its energy to a sensitizer thus exciting it longer and easier to quantify light emission is often observed The color that is the wavelength brightness and duration of emission depend upon the sensitizer used Usually for a certain chemical reaction many different sensitizers can be used List of some common sensitizers edit Violanthrone Isoviolanthrone Fluorescein Rubrene 9 10 Diphenylanthracene Tetracene 13 13 Dibenzantronile Levulinic AcidFluorescence spectroscopy editFluorescence spectroscopy aka fluorometry or spectrofluorometry is a type of electromagnetic spectroscopy which analyzes fluorescence from a sample It involves using a beam of light usually ultraviolet light that excites the electrons in molecules of certain compounds and causes them to emit light of a lower energy typically but not necessarily visible light A complementary technique is absorption spectroscopy 15 16 Devices that measure fluorescence are called fluorometers or fluorimeters Absorption spectroscopy editAbsorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation as a function of frequency or wavelength due to its interaction with a sample The sample absorbs energy i e photons from the radiating field The intensity of the absorption varies as a function of frequency and this variation is the absorption spectrum Absorption spectroscopy is performed across the electromagnetic spectrum 15 16 See also editPhotoelectrochemistry Ionization energy Isomerization Photoionization mode Photochromism Photoelectric effect Photoionization detectorReferences edit Gerischer Heinz 1985 Semiconductor electrodes and their interaction with light In Schiavello Mario ed Photoelectrochemistry Photocatalysis and Photoreactors Fundamentals and Developments Springer p 39 ISBN 978 90 277 1946 1 Madden R P Codling K 1965 Two electron states in Helium Astrophysical Journal 141 364 Bibcode 1965ApJ 141 364M doi 10 1086 148132 Mammana A et al 2011 A Chiroptical Photoswitchable DNA Complex PDF Journal of Physical Chemistry B 115 40 11581 11587 doi 10 1021 jp205893y PMID 21879715 S2CID 33375716 Vachon J et al 2014 An ultrafast surface bound photo active molecular motor Photochemical and Photobiological Sciences 13 2 241 246 doi 10 1039 C3PP50208B PMID 24096390 S2CID 23165784 a b c d Radiation Encyclopaedia Britannica Online Retrieved 9 November 2009 Carroll B W Ostlie D A 2007 An Introduction to Modern Astrophysics Addison Wesley p 121 ISBN 978 0 321 44284 0 Delone N B Krainov V P 1998 Tunneling and barrier suppression ionization of atoms and ions in a laser radiation field Physics Uspekhi 41 5 469 485 Bibcode 1998PhyU 41 469D doi 10 1070 PU1998v041n05ABEH000393 S2CID 250763981 Dichiara A et al 2005 Cross shell multielectron ionization of xenon by an ultrastrong laser field Proceedings of the Quantum Electronics and Laser Science Conference Vol 3 Optical Society of America pp 1974 1976 doi 10 1109 QELS 2005 1549346 ISBN 1 55752 796 2 Deng Z Eberly J H 1985 Multiphoton absorption above ionization threshold by atoms in strong laser fields Journal of the Optical Society of America B 2 3 491 Bibcode 1985JOSAB 2 486D doi 10 1364 JOSAB 2 000486 Agostini P et al 1979 Free Free Transitions Following Six Photon Ionization of Xenon Atoms Physical Review Letters 42 17 1127 1130 Bibcode 1979PhRvL 42 1127A doi 10 1103 PhysRevLett 42 1127 Nandor M et al 1999 Detailed comparison of above threshold ionization spectra from accurate numerical integrations and high resolution measurements Physical Review A 60 3 1771 1774 Bibcode 1999PhRvA 60 1771N doi 10 1103 PhysRevA 60 R1771 Dekorsy T et al 1996 THz electromagnetic emission by coherent infrared active phonons PDF Physical Review B 53 7 4005 4014 Bibcode 1996PhRvB 53 4005D doi 10 1103 PhysRevB 53 4005 PMID 9983955 a b c d e Photochemical equivalence law Encyclopaedia Britannica Online Retrieved 7 November 2009 a b c Photosensitization Encyclopaedia Britannica Online Retrieved 10 November 2009 a b Hollas J M 2004 Modern Spectroscopy 4th ed John Wiley amp Sons ISBN 978 0 470 84416 8 a b Harris D C Bertolucci M D 1978 Symmetry and Spectroscopy An introduction to vibrational and electronic spectroscopy Reprint ed Dover Publications ISBN 978 0 486 66144 5 Retrieved from https en wikipedia org w index php title Photoelectrochemical process amp oldid 1189334999, wikipedia, wiki, book, books, library,

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