Photon upconversion
Encyclopedia
Photon upconversion is a process in which the sequential absorption
of two or more photon
s leads to the emission
of light
at shorter wavelength
than the excitation wavelength. It is a anti-Stokes
type emission. An example is the conversion of infrared light to visible light. Materials by which upconversion can take place often contain ions of d-block
and f-block
elements. Examples of these ions are Ti
2+, Ni
2+, Mo
3+, Re
4+, and Os
4+.
Three basic mechanisms are energy transfer upconversion
, excited-state absorption (ESA) and photon avalanche (PA). Upconversion should be distinguished from two-photon absorption
and second-harmonic generation. An early proposal (a solid-state IR quantum counter) was made by N. Bloembergen
in 1959 The process was first observed by F. Auzel in 1966
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...
of two or more photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s leads to the emission
Emission spectrum
The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted by the element's atoms or the compound's molecules when they are returned to a lower energy state....
of light
Light
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...
at shorter wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
than the excitation wavelength. It is a anti-Stokes
Stokes shift
Stokes shift is the difference between positions of the band maxima of the absorption and emission spectra of the same electronic transition. It is named after Irish physicist George G. Stokes. When a system absorbs a photon, it gains energy and enters an excited state...
type emission. An example is the conversion of infrared light to visible light. Materials by which upconversion can take place often contain ions of d-block
D-block
The d-block is the portion of the periodic table that contains the element groups 3-12. These groups correspond to the filling of the atomic d-orbital subshell, with electron configurations ranging from s2d1 to s2d10...
and f-block
F-block
The f-block of the periodic table of the elements consists of those elements whose atoms or ions have valence electrons in f-orbitals. Actual electronic configurations may be slightly different from what is predicted by the Aufbau principle...
elements. Examples of these ions are Ti
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
2+, Ni
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
2+, Mo
Molybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...
3+, Re
Rhenium
Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-white, heavy, third-row transition metal in group 7 of the periodic table. With an average concentration of 1 part per billion , rhenium is one of the rarest elements in the Earth's crust. The free element has...
4+, and Os
Osmium
Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...
4+.
Three basic mechanisms are energy transfer upconversion
Energy transfer upconversion
Energy Transfer Upconversion or ETU is a physical principle that involves the excitation of a laser-active ion to a level above that which would be achieved by simple absorption of a pump photon, the required additional energy being transferred from another laser-active ion undergoing nonradiative...
, excited-state absorption (ESA) and photon avalanche (PA). Upconversion should be distinguished from two-photon absorption
Two-photon absorption
Two-photon absorption is the simultaneous absorption of two photons of identical or different frequencies in order to excite a molecule from one state to a higher energy electronic state. The energy difference between the involved lower and upper states of the molecule is equal to the sum of the...
and second-harmonic generation. An early proposal (a solid-state IR quantum counter) was made by N. Bloembergen
Nicolaas Bloembergen
Nicolaas Bloembergen is a Dutch-American physicist and Nobel laureate.He received his Ph.D. degree from University of Leiden in 1948; while pursuing his PhD at Harvard, Bloembergen also worked part-time as a graduate research assistant for Edward Mills Purcell at the MIT Radiation Laboratory...
in 1959 The process was first observed by F. Auzel in 1966