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70-466: Lume is a short term for the luminous phosphorescent glowing solution applied on watch dials . There are some people who "relume" watches, or replace faded lume. Formerly, lume consisted mostly of radium ; however, radium is radioactive and has been mostly replaced on new watches by less bright, but less toxic compounds. After radium was effectively outlawed in 1968, tritium became the luminescent material of choice, because, while still radioactive, it

140-401: A substitutional defect occurs, while an interstitial defect occurs when a much smaller atom gets trapped in the "interstices", or the spaces between atoms. In contrast, amorphous materials have no "long-range order" (beyond the space of a few atoms in any direction), thus by definition are filled with defects. When a defect occurs, depending on the type and material, it can create a hole, or

210-441: A "trap". For example, a missing oxygen atom from a zinc oxide compound creates a hole in the lattice, surrounded by unbound zinc-atoms. This creates a net force or attraction that can be measured in electron-volts . When a high-energy photon strikes one of the zinc atoms, its electron absorbs the photon and is thrown out into a higher orbit. The electron may then enter the trap and be held in place (out of its normal orbit) by

280-414: A brighter yet short-lived emission, while lower temperatures produce a dimmer but longer-lasting glow. Temperatures that are too hot or cold, depending on the substance, may not allow the accumulation or release of energy at all. The ideal depth of trap for persistent phosphorescence at room temperature is typically between 0.6 and 0.7 electron-volts. If the phosphorescent quantum yield is high, that is, if

350-787: A combination of different types of glass; each type of glass refracts light in a different way. By using combinations of different types of glass, lens manufacturers are able to cancel out or significantly reduce unwanted characteristics; chromatic aberration being the most important. The best of such lens designs are often called apochromatic (see above). Fluoro-crown glass (such as Schott FK51) usually in combination with an appropriate "flint" glass (such as Schott KzFSN 2) can give very high performance in telescope objective lenses, as well as microscope objectives, and camera telephoto lenses. Fluorite elements are similarly paired with complementary "flint" elements (such as Schott LaK 10). The refractive qualities of fluorite and of certain flint elements provide

420-665: A constituent of sedimentary rocks either as grains or as the cementing material in sandstone . It is a common mineral mainly distributed in South Africa, China, Mexico, Mongolia, the United Kingdom, the United States, Canada, Tanzania, Rwanda and Argentina. The world reserves of fluorite are estimated at 230 million tonnes (Mt) with the largest deposits being in South Africa (about 41 Mt), Mexico (32 Mt) and China (24 Mt). China

490-542: A lower and more uniform dispersion across the spectrum of visible light, thereby keeping colors focused more closely together. Lenses made with fluorite are superior to fluoro-crown based lenses, at least for doublet telescope objectives; but are more difficult to produce and more costly. The use of fluorite for prisms and lenses was studied and promoted by Victor Schumann near the end of the 19th century. Naturally occurring fluorite crystals without optical defects were only large enough to produce microscope objectives. With

560-661: A person or object in front of a phosphorescent screen which temporarily captures the shadow. The screen or wall is painted with a glow-in-the-dark product that contains phosphorescent compounds. Publicly, these shadow walls can be found at certain science museums. Fluorspar Fluorite (also called fluorspar ) is the mineral form of calcium fluoride , CaF 2 . It belongs to the halide minerals . It crystallizes in isometric cubic habit , although octahedral and more complex isometric forms are not uncommon. The Mohs scale of mineral hardness , based on scratch hardness comparison , defines value 4 as fluorite. Pure fluorite

630-449: A phenomenon usually only reported in synthetic materials. One fluorescent variety of fluorite is chlorophane , which is reddish or purple in color and fluoresces brightly in emerald green when heated ( thermoluminescence ), or when illuminated with ultraviolet light. The color of visible light emitted when a sample of fluorite is fluorescing depends on where the original specimen was collected; different impurities having been included in

700-423: A second after the illumination is switched off. Conversely, when the stored energy is due to persistent phosphorescence, an entirely different process occurs without a fluorescence precursor. When electrons become trapped within a defect in the atomic or molecular lattice, light is prevented from reemitting until the electron can escape. To escape, the electron needs a boost of thermal energy to help spring it out of

770-465: A uniquely high transparency at this wavelength. Fluorite objective lenses are manufactured by the larger microscope firms (Nikon, Olympus , Carl Zeiss and Leica). Their transparence to ultraviolet light enables them to be used for fluorescence microscopy . The fluorite also serves to correct optical aberrations in these lenses. Nikon has previously manufactured at least one fluorite and synthetic quartz element camera lens (105 mm f/4.5 UV) for

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840-643: Is associated with quartz and leafy aggregates of baryte. In the Emilio mine, in Loroñe, Colunga , the fluorite crystals, cubes with small modifications of other figures, are colourless and transparent. They can reach 10 cm of edge. In the Moscona mine, in Villabona, the fluorite crystals, cubic without modifications of other shapes, are yellow, up to 3 cm of edge. They are associated with large crystals of calcite and barite. One of

910-566: Is colourless and transparent, both in visible and ultraviolet light, but impurities usually make it a colorful mineral and the stone has ornamental and lapidary uses. Industrially, fluorite is used as a flux for smelting, and in the production of certain glasses and enamels. The purest grades of fluorite are a source of fluoride for hydrofluoric acid manufacture, which is the intermediate source of most fluorine-containing fine chemicals . Optically clear transparent fluorite has anomalous partial dispersion , that is, its refractive index varies with

980-479: Is commonly present. The color of the fluorite is determined by factors including impurities, exposure to radiation, and the absence of voids of the color centers . Fluorite is a major source of hydrogen fluoride , a commodity chemical used to produce a wide range of materials. Hydrogen fluoride is liberated from the mineral by the action of concentrated sulfuric acid : The resulting HF is converted into fluorine, fluorocarbons , and diverse fluoride materials. As of

1050-437: Is created via a chemical reaction. The light emission tracks the kinetic progress of the underlying chemical reaction. The excited state will then transfer to a dye molecule, also known as a sensitizer or fluorophor , and subsequently fluoresce back to the ground state. Common pigments used in phosphorescent materials include zinc sulfide and strontium aluminate . Use of zinc sulfide for safety related products dates back to

1120-412: Is decoration. Stars made of glow-in-the-dark plastic are placed on walls, ceilings, or hanging from strings make a room look like the night sky. Other objects like figurines, cups, posters, lamp fixtures, toys and bracelet beads may also glow. Using blacklights makes these things glow brightly, common at raves , bedrooms, theme parks, and festivals. A shadow wall is created when a light flashes upon

1190-511: Is derived from the Latin verb fluere , meaning to flow . The mineral is used as a flux in iron smelting to decrease the viscosity of slag . The term flux comes from the Latin adjective fluxus , meaning flowing, loose, slack . The mineral fluorite was originally termed fluorspar and was first discussed in print in a 1530 work Bermannvs sive de re metallica dialogus [Bermannus; or dialogue about

1260-610: Is leading the world production with about 3 Mt annually (in 2010), followed by Mexico (1.0 Mt), Mongolia (0.45 Mt), Russia (0.22 Mt), South Africa (0.13 Mt), Spain (0.12 Mt) and Namibia (0.11 Mt). One of the largest deposits of fluorspar in North America is located on the Burin Peninsula , Newfoundland , Canada. The first official recognition of fluorspar in the area was recorded by geologist J.B. Jukes in 1843. He noted an occurrence of "galena" or lead ore and fluoride of lime on

1330-401: Is much less potent than radium, tritium being about as radioactive as an x-ray, the decrease in radioactivity resulting from a diminishment of strength and quantity of the beta waves that are given off by tritium as an element. Common pigments used in lume include the phosphorescent pigments zinc sulfide and strontium aluminate . Use of zinc sulfide for safety related products dates back to

1400-618: Is so common that the motif is called the fluorite structure . Element substitution for the calcium cation often includes strontium and certain rare-earth elements (REE), such as yttrium and cerium . Fluorite forms as a late-crystallizing mineral in felsic igneous rocks typically through hydrothermal activity. It is particularly common in granitic pegmatites. It may occur as a vein deposit formed through hydrothermal activity particularly in limestones. In such vein deposits it can be associated with galena , sphalerite , barite , quartz , and calcite . Fluorite can also be found as

1470-683: Is widely available and was sometimes known by the Eastman Kodak trademarked name "Irtran-3", although this designation is obsolete. Fluorite should not be confused with fluoro-crown (or fluorine crown) glass, a type of low-dispersion glass that has special optical properties approaching fluorite. True fluorite is not a glass but a crystalline material. Lenses or optical groups made using this low dispersion glass as one or more elements exhibit less chromatic aberration than those utilizing conventional, less expensive crown glass and flint glass elements to make an achromatic lens . Optical groups employ

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1540-484: The 1930s. The development of strontium aluminate pigments in 1993 was spurred on by the need to find a substitute for glow-in-the-dark materials with high luminance and long phosphorescence, especially those that used promethium . This led to the discovery by Yasumitsu Aoki (Nemoto & Co.) of materials with luminance approximately 10 times greater than zinc sulfide and phosphorescence approximately 10 times longer. This has relegated most zinc sulfide based products to

1610-463: The 1930s. However, the development of strontium oxide aluminate, with a luminance approximately 10 times greater than zinc sulfide, has relegated most zinc sulfide based products to the novelty category. Strontium oxide aluminate based pigments are now used in exit signs, pathway marking, and other safety related signage. Strontium aluminate based afterglow pigments are marketed under brandnames like Super-LumiNova , Watchlume Co, NoctiLumina, and Glow in

1680-407: The 1950s and 1960s did advances in quantum electronics , spectroscopy , and lasers provide a measure to distinguish between the various processes that emit the light, although in common speech the distinctions are still often rather vague. In simple terms, phosphorescence is a process in which energy absorbed by a substance is released relatively slowly in the form of light. This is in some cases

1750-462: The 1990s, as newer designs using fluoro-crown glass, including triplets, have offered comparable performance at lower prices. Fluorite and various combinations of fluoride compounds can be made into synthetic crystals which have applications in lasers and special optics for UV and infrared. Exposure tools for the semiconductor industry make use of fluorite optical elements for ultraviolet light at wavelengths of about 157 nanometers . Fluorite has

1820-463: The Dark (Phosphorescent) Technologies. Phosphorescence In a general sense, there is no distinct boundary between the emission times of fluorescence and phosphorescence (i.e.: if a substance glows under a black light it is generally considered fluorescent, and if it glows in the dark it is often simply called phosphorescent). In a modern, scientific sense, the phenomena can usually be classified by

1890-501: The Greek suffix -φόρος ( -phoros ), meaning "to bear", combined with the Latin suffix -escentem , meaning "becoming of", "having a tendency towards", or "with the essence of". Thus, phosphorescence literally means "having a tendency to bear light". It was first recorded in 1766. The term phosphor had been used since the Middle Ages to describe minerals that glowed in the dark. One of

1960-594: The Latin terms murrina and myrrhina refer to fluorite. In book 37 of his Naturalis Historia , Pliny the Elder describes it as a precious stone with purple and white mottling, and noted that the Romans prized objects carved from it. Fluorite crystallizes in a cubic motif . Crystal twinning is common and adds complexity to the observed crystal habits . Fluorite has four perfect cleavage planes that help produce octahedral fragments. The structural motif adopted by fluorite

2030-401: The addition of AlF 3 , the majority of which react with excess sodium from the alumina to form Na 3 AlF 6 . Natural fluorite mineral has ornamental and lapidary uses. Fluorite may be drilled into beads and used in jewelry, although due to its relative softness it is not widely used as a semiprecious stone. It is also used for ornamental carvings, with expert carvings taking advantage of

2100-450: The advent of synthetically grown fluorite crystals in the 1950s - 60s, it could be used instead of glass in some high-performance optical telescope and camera lens elements. In telescopes, fluorite elements allow high-resolution images of astronomical objects at high magnifications . Canon Inc. produces synthetic fluorite crystals that are used in their better telephoto lenses . The use of fluorite for telescope lenses has declined since

2170-419: The attraction. To trigger the release of the energy, a random spike in thermal energy of sufficient magnitude is needed to boost the electron out of the trap and back into its normal orbit. Once in orbit, the electron's energy can drop back to normal (ground state) resulting in the release of a photon. The release of energy in this way is a completely random process, governed mostly by the average temperature of

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2240-428: The blue fluorescence seen in fluorites from certain parts of Great Britain responsible for the naming of the phenomenon of fluorescence itself, has been attributed to the presence of inclusions of divalent europium in the crystal. Natural samples containing rare earth impurities such as erbium have also been observed to display upconversion fluorescence , in which infrared light stimulates emission of visible light,

2310-405: The classic Blue John stone. George Gabriel Stokes named the phenomenon of fluorescence from fluorite, in 1852. Many samples of fluorite exhibit fluorescence under ultraviolet light , a property that takes its name from fluorite. Many minerals, as well as other substances, fluoresce. Fluorescence involves the elevation of electron energy levels by quanta of ultraviolet light, followed by

2380-523: The company was planned to develop a new shipping port on the west side of Burin Peninsula as a more affordable means of moving their product to markets, and they successfully sent the first shipload of ore from the new port on July 31, 2021. This marks the first time in 30 years that ore has been shipped directly out of St. Lawrence. Cubic crystals up to 20 cm across have been found at Dalnegorsk , Russia. The largest documented single crystal of fluorite

2450-557: The crystal lattice in different places. Neither does all fluorite fluoresce equally brightly, even from the same locality. Therefore, ultraviolet light is not a reliable tool for the identification of specimens, nor for quantifying the mineral in mixtures. For example, among British fluorites, those from Northumberland , County Durham , and eastern Cumbria are the most consistently fluorescent, whereas fluorite from Yorkshire , Derbyshire , and Cornwall , if they fluoresce at all, are generally only feebly fluorescent. Fluorite also exhibits

2520-1084: The excited triplet state, and, even if T 1 is formed, phosphorescence is most frequently outcompeted by non-radiative pathways. One strategy to enhance the ISC and phosphorescence is the incorporation of heavy atoms, which increase spin-orbit coupling (SOC). Additionally, the SOC (and therefore the ISC) can be promoted by coupling n-π* and π-π* transitions with different angular momenta, also known as Mostafa El-Sayed 's rule. Such transitions are typically exhibited by carbonyl or triazine derivatives, and most organic room-temperature phosphorescent (ORTP) materials incorporate such moieties. In turn, to inhibit competitive non-radiative deactivation pathways, including vibrational relaxation and oxygen quenching and triplet-triplet annihilations, organic phosphors have to be embedded in rigid matrices such as polymers, and molecular solids (crystals, covalent organic frameworks, and others). In 1974 Becky Schroeder

2590-421: The fluorite with sulfuric acid . Internationally, acid-grade fluorite is also used in the production of AlF 3 and cryolite (Na 3 AlF 6 ), which are the main fluorine compounds used in aluminium smelting. Alumina is dissolved in a bath that consists primarily of molten Na 3 AlF 6 , AlF 3 , and fluorite (CaF 2 ) to allow electrolytic recovery of aluminium. Fluorine losses are replaced entirely by

2660-422: The formation of a picture as the electron beam scans the screen, but fast enough to prevent the frames from blurring together. Even substances commonly associated with fluorescence may in fact be prone to phosphorescence, such as the liquid dyes found in highlighter pens, which is a common problem in liquid dye lasers . The onset of phosphorescence in this case can sometimes be reduced or delayed significantly by

2730-505: The glow-in-the-dark toys, stickers, paint, and clock dials that glow after being charged with a bright light such as in any normal reading or room light. Typically, the glow slowly fades out, sometimes within a few minutes or up to a few hours in a dark room. The study of phosphorescent materials led to the discovery of radioactive decay . The term phosphorescence comes from the Ancient Greek word φῶς ( phos ), meaning "light", and

2800-403: The ground state, and 1 the excited state). Transitions can also occur to higher energy levels, but the first excited state is denoted for simplicity. Solid materials typically come in two main types: crystalline and amorphous. In either case, a lattice or network of atoms and molecules form. In crystals, the lattice is a very neat, uniform assembly. However, nearly all crystals have defects in

2870-429: The late 1990s, five billion kilograms were mined annually. There are three principal types of industrial use for natural fluorite, commonly referred to as "fluorspar" in these industries, corresponding to different grades of purity. Metallurgical grade fluorite (60–85% CaF 2 ), the lowest of the three grades, has traditionally been used as a flux to lower the melting point of raw materials in steel production to aid

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2940-435: The material versus the "depth" of the trap, or how many electron-volts it exerts. A trap that has a depth of 2.0 electron-volts would require a great amount of thermal energy (very high temperature) to overcome the attraction, while at a depth of 0.1 electron-volts very little heat (very cold temperature) is needed for the trap to even hold an electron. Generally, higher temperatures cause a faster release of energy, resulting in

3010-579: The mechanism used for glow-in-the-dark materials which are "charged" by exposure to light. Unlike the relatively swift reactions in fluorescence, such as those seen in laser mediums like the common ruby , phosphorescent materials "store" absorbed energy for a longer time, as the processes required to reemit energy occur less often. However, timescale is still only a general distinction, as there are slow-emitting fluorescent materials, for example uranyl salts , and, likewise, some phosphorescent materials like zinc sulfide (in violet) are very fast. Scientifically,

3080-756: The most famous of the older-known localities of fluorite is Castleton in Derbyshire , England , where, under the name of "Derbyshire Blue John", purple-blue fluorite was extracted from several mines or caves. During the 19th century, this attractive fluorite was mined for its ornamental value. The mineral Blue John is now scarce, and only a few hundred kilograms are mined each year for ornamental and lapidary use. Mining still takes place in Blue John Cavern and Treak Cliff Cavern . Recently discovered deposits in China have produced fluorite with coloring and banding similar to

3150-403: The most famous, but not the first, was Bolognian phosphor. Around 1604, Vincenzo Casciarolo discovered a " lapis solaris " near Bologna, Italy. Once heated in an oxygen-rich furnace , it thereafter absorbed sunlight and glowed in the dark. In 1677, Hennig Brand isolated a new element that glowed due to a chemiluminescent reaction when exposed to air, and named it " phosphorus ". In contrast,

3220-513: The nature of metals], by Georgius Agricola , as a mineral noted for its usefulness as a flux. Agricola, a German scientist with expertise in philology , mining , and metallurgy, named fluorspar as a Neo-Latinization of the German Flussspat from Fluss ( stream , river ) and Spat (meaning a nonmetallic mineral akin to gypsum , spærstān, spear stone , referring to its crystalline projections). In 1852, fluorite gave its name to

3290-428: The novelty category. Strontium aluminate based pigments are now used in exit signs, pathway marking, and other safety related signage. Since both phosphorescence (transition from T 1 to S 0 ) and the generation of T 1 from an excited singlet state (e.g., S 1 ) via intersystem crossing (ISC) are spin-forbidden processes, most organic materials exhibit insignificant phosphorescence as they mostly fail to populate

3360-401: The phenomena are classified by the different mechanisms that produce the light, as materials that phosphoresce may be suitable for some purposes such as lighting, but may be completely unsuitable for others that require fluorescence, like lasers. Further blurring the lines, a substance may emit light by one, two, or all three mechanisms depending on the material and excitation conditions. When

3430-438: The phenomenon of fluorescence , which is prominent in fluorites from certain locations, due to certain impurities in the crystal. Fluorite also gave the name to its constitutive element fluorine . Currently, the word "fluorspar" is most commonly used for fluorite as an industrial and chemical commodity, while "fluorite" is used mineralogically and in most other senses. In archeology, gemmology, classical studies, and Egyptology,

3500-406: The phosphor coatings used in fluorescent lamps , where phosphorescence on the order of milliseconds or longer is useful for filling in the "off-time" between AC current cycles, helping to reduce "flicker". Phosphors with faster decay times are used in applications like the pixels excited by free electrons ( cathodoluminescence ) in cathode-ray tube television-sets , which are slow enough to allow

3570-408: The photons involved matches the available energy states and allowed transitions of the substrate. In the special case of phosphorescence, the electron which absorbed the photon (energy) undergoes an unusual intersystem crossing into an energy state of different (usually higher) spin multiplicity ( see term symbol ), usually a triplet state . As a result, the excited electron can become trapped in

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3640-782: The production of ultraviolet images . Konica produced a fluorite lens for their SLR cameras – the Hexanon 300 mm f/6.3. In 2012, the first source of naturally occurring fluorine gas was found in fluorite mines in Bavaria, Germany. It was previously thought that fluorine gas did not occur naturally because it is so reactive, and would rapidly react with other chemicals. Fluorite is normally colorless, but some varied forms found nearby look black, and are known as 'fetid fluorite' or antozonite . The minerals, containing small amounts of uranium and its daughter products, release radiation sufficiently energetic to induce oxidation of fluoride anions within

3710-433: The progressive falling back of the electrons into their previous energy state, releasing quanta of visible light in the process. In fluorite, the visible light emitted is most commonly blue, but red, purple, yellow, green, and white also occur. The fluorescence of fluorite may be due to mineral impurities, such as yttrium and ytterbium , or organic matter, such as volatile hydrocarbons in the crystal lattice. In particular,

3780-512: The property of thermoluminescence . Fluorite is allochromatic, meaning that it can be tinted with elemental impurities. Fluorite comes in a wide range of colors and has consequently been dubbed "the most colorful mineral in the world". Every color of the rainbow in various shades is represented by fluorite samples, along with white, black, and clear crystals. The most common colors are purple, blue, green, yellow, or colorless. Less common are pink, red, white, brown, and black. Color zoning or banding

3850-592: The refractive index of calcium fluoride shows some non-linearity at high power densities, which has inhibited its use for this purpose. In the early years of the 21st century, the stepper market for calcium fluoride collapsed, and many large manufacturing facilities have been closed. Canon and other manufacturers have used synthetically grown crystals of calcium fluoride components in lenses to aid apochromatic design, and to reduce light dispersion . This use has largely been superseded by newer glasses and computer-aided design. As an infrared optical material, calcium fluoride

3920-444: The removal of impurities, and later in the production of aluminium . Ceramic grade fluorite (85–95% CaF 2 ) is used in the manufacture of opalescent glass , enamels , and cooking utensils. The highest grade, "acid grade fluorite" (97% or more CaF 2 ), accounts for about 95% of fluorite consumption in the US where it is used to make hydrogen fluoride and hydrofluoric acid by reacting

3990-437: The stacking sequence of these molecules and atoms. A vacancy defect , where an atom is simply missing from its place, leaving an empty "hole", is one type of defect. Sometimes atoms can move from place to place within the lattice, creating Schottky defects or Frenkel defects . Other defects can occur from impurities in the lattice. For example, when a normal atom is substituted by a different atom of much larger or smaller size,

4060-499: The stone's zonation. In the laboratory, calcium fluoride is commonly used as a window material for both infrared and ultraviolet wavelengths, since it is transparent in these regions (about 0.15 μm to 9 μm) and exhibits an extremely low change in refractive index with wavelength. Furthermore, the material is attacked by few reagents. At wavelengths as short as 157 nm, a common wavelength used for semiconductor stepper manufacture for integrated circuit lithography ,

4130-437: The stored energy becomes locked in by the spin of the atomic electrons , a triplet state can occur, slowing the emission of light, sometimes by several orders of magnitude. Because the atoms usually begin in a singlet state of spin, favoring fluorescence, these types of phosphors typically produce both types of emission during illumination, and then a dimmer afterglow of strictly phosphorescent light typically lasting less than

4200-432: The substance has a large number of traps of the correct depth, this substance will release a significant amount of light over a long period of time, creating a so-called "glow in the dark" material. Some examples of glow-in-the-dark materials do not glow by phosphorescence. For example, glow sticks glow due to a chemiluminescent process which is commonly mistaken for phosphorescence. In chemiluminescence, an excited state

4270-406: The term luminescence (from the Latin lumen for "light"), was coined by Eilhardt Wiedemann in 1888 as a term to refer to "light without heat", while "fluorescence" by Sir George Stokes in 1852, when he noticed that, when exposing a solution of quinine sulfate to light refracted through a prism , the solution glowed when exposed to the mysterious invisible-light (now known to be UV light) beyond

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4340-644: The three different mechanisms that produce the light, and the typical timescales during which those mechanisms emit light. Whereas fluorescent materials stop emitting light within nanoseconds (billionths of a second) after the excitation radiation is removed, phosphorescent materials may continue to emit an afterglow ranging from a few microseconds to many hours after the excitation is removed. There are two separate mechanisms that may produce phosphorescence, called triplet phosphorescence (or simply phosphorescence) and persistent phosphorescence (or persistent luminescence ): Everyday examples of phosphorescent materials are

4410-411: The trap and back into orbit around the atom. Only then can the atom emit a photon. Thus, persistent phosphorescence is highly dependent on the temperature of the material. 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

4480-421: The triplet state with only "forbidden" transitions available to return to the lower energy singlet state. These transitions, although "forbidden", will still occur in quantum mechanics but are kinetically unfavored and thus progress at significantly slower time scales. Most phosphorescent compounds are still relatively fast emitters, with triplet decay-times in the order of milliseconds. Common examples include

4550-401: The use of triplet-quenching agents. S 0 + h ν → S 1 → T 1 → S 0 + h ν ′   {\displaystyle S_{0}+h\nu \to S_{1}\to T_{1}\to S_{0}+h\nu ^{\prime }\ } where S is a singlet and T a triplet whose subscripts denote states (0 is

4620-718: The violet end of the spectrum. Stokes formed the term from a combination of fluorspar and opalescence (preferring to use a mineral instead of a solution), albeit it was later discovered that fluorspar glows due to phosphorescence. There was much confusion between the meanings of these terms throughout the late nineteenth to mid-twentieth centuries. Whereas the term "fluorescence" tended to refer to luminescence that ceased immediately (by human-eye standards) when removed from excitation, "phosphorescence" referred to virtually any substance that glowed for appreciable periods in darkness, sometimes to include even chemiluminescence (which occasionally produced substantial amounts of heat). Only after

4690-420: The wavelength of light in a manner that differs from that of commonly used glasses, so fluorite is useful in making apochromatic lenses , and particularly valuable in photographic optics. Fluorite optics are also usable in the far-ultraviolet and mid-infrared ranges, where conventional glasses are too opaque for use. Fluorite also has low dispersion, and a high refractive index for its density. The word fluorite

4760-597: The west side of St. Lawrence harbour. It is recorded that interest in the commercial mining of fluorspar began in 1928 with the first ore being extracted in 1933. Eventually, at Iron Springs Mine, the shafts reached depths of 970 feet (300 m). In the St. Lawrence area, the veins are persistent for great lengths and several of them have wide lenses . The area with veins of known workable size comprises about 60 square miles (160 km ). In 2018, Canada Fluorspar Inc. commenced mine production again in St. Lawrence; in spring 2019,

4830-437: Was a cube 2.12 meters in size and weighing approximately 16 tonnes. In Asturias ( Spain ) there are several fluorite deposits known internationally for the quality of the specimens they have yielded. In the area of Berbes , Ribadesella , fluorite appears as cubic crystals, sometimes with dodecahedron modifications, which can reach a size of up to 10 cm of edge, with internal colour zoning, almost always violet in colour. It

4900-541: Was given a US patent for her invention of the "Glow Sheet" which used phosphorescent lines under writing paper to help people write in low-light conditions. Glow in the dark material is added to the plastic blend used in injection molds to make some disc golf discs, which allow the game to be played at night. Often clock faces of watches are painted with phosphorescent colours. Therefore, they can be used in absolute dark environments for several hours after having been exposed to bright light. A common use of phosphorescence

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