Luminophore
Encyclopedia
A luminophore is an atom or atomic grouping in a chemical compound
that manifests luminescence
. There exist organic and inorganic luminophores. It should be stressed that the correct, textbook terminology is luminophore, not lumophore, although the latter term has been frequently but erroneously used in the chemical literature.
Luminophores can be divided into two subcategories: fluorophore
s and phosphor
s. The difference between luminophores belonging to these two subcategories is derived from the nature of the excited state
responsible for the emission of photon
s. Some luminophores, however, cannot be classified as being exclusively fluorophore
s or phosphors and exist in the gray area in between. Such cases include transition metal
complexes (such as ruthenium
tris-2,2'-bipyridine
) whose luminescence comes from an excited (nominally triplet) metal-to-ligand charge transfer (MLCT) state, but which is not a true triplet-state in the strict sense of the definition; and colloidal quantum dots, whose emissive state does not have either a purely singlet or triplet spin.
Most luminophores consist of conjugated pi systems
or transition metal
complexes. There exist purely inorganic luminophores, such as zinc sulfide
doped with rare earth metal ions, rare earth metal oxysulfides doped with other rare earth metal ions, yttrium oxide doped with rare earth metal ions, zinc orthosilicate doped with manganese ions, etc. Luminophores can be observed in action in fluorescent lights, TV screens, computer monitor screens, organic light-emitting diode
s and bioluminescence
.
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...
that manifests luminescence
Luminescence
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...
. There exist organic and inorganic luminophores. It should be stressed that the correct, textbook terminology is luminophore, not lumophore, although the latter term has been frequently but erroneously used in the chemical literature.
Luminophores can be divided into two subcategories: fluorophore
Fluorophore
A fluorophore, in analogy to a chromophore, is a component of a molecule which causes a molecule to be fluorescent. It is a functional group in a molecule which will absorb energy of a specific wavelength and re-emit energy at a different wavelength...
s and phosphor
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
s. The difference between luminophores belonging to these two subcategories is derived from the nature of the excited state
Excited state
Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state....
responsible for the emission of 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. Some luminophores, however, cannot be classified as being exclusively fluorophore
Fluorophore
A fluorophore, in analogy to a chromophore, is a component of a molecule which causes a molecule to be fluorescent. It is a functional group in a molecule which will absorb energy of a specific wavelength and re-emit energy at a different wavelength...
s or phosphors and exist in the gray area in between. Such cases include transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
complexes (such as ruthenium
Ruthenium
Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element...
tris-2,2'-bipyridine
2,2'-Bipyridine
2,2'-Bipyridine is a organic compound with the formula . This colorless solid, commonly abbreviated bipy or bpy , is an important isomer of the bipyridine family. It is a bidentate chelating ligand, forming complexes with many transition metals...
) whose luminescence comes from an excited (nominally triplet) metal-to-ligand charge transfer (MLCT) state, but which is not a true triplet-state in the strict sense of the definition; and colloidal quantum dots, whose emissive state does not have either a purely singlet or triplet spin.
Most luminophores consist of conjugated pi systems
Conjugated system
In chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in compounds with alternating single and multiple bonds, which in general may lower the overall energy of the molecule and increase stability. Lone pairs, radicals or carbenium ions may be part of the...
or transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
complexes. There exist purely inorganic luminophores, such as zinc sulfide
Zinc sulfide
Zinc sulfide is a inorganic compound with the formula ZnS. ZnS is the main form of zinc in nature, where it mainly occurs as the mineral sphalerite...
doped with rare earth metal ions, rare earth metal oxysulfides doped with other rare earth metal ions, yttrium oxide doped with rare earth metal ions, zinc orthosilicate doped with manganese ions, etc. Luminophores can be observed in action in fluorescent lights, TV screens, computer monitor screens, organic light-emitting diode
Organic light-emitting diode
An OLED is a light-emitting diode in which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. This layer of organic semiconductor material is situated between two electrodes...
s 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...
.