Luminescence Triboluminescence

Emission of li t accompanying the crystallization of certain crystals from solution and probably arising from cleavages occurring during the growth of individual crystals. Thus, it is a form of triboluminescence. Luminescence which appears when crystals dissolve is termed lyoluminescence. 

Piezoluminescence is luminescence brought about by pressure (see also triboluminescence). 

The same laboratory describes a group of complexes with a unique property among metal complexes, referred to as luminescence tribochromism [39], which is a substantial change in the emission of the solid upon application of pressure. This phenomenon contrasts with the more common triboluminescence, which refers to the transient emission seen upon sample grinding or crushing. In this case, the effect was observed in a set of complexes of formula [Au2( J.-TU)((j,-dppm)]Y and [Au2( i-MeTU)( i-dppm)]Y (TU = 2-thiouracyl MeTU = 6-methyl-2-thiouracyl Y = CF3COOT NCV, CKV, Au(CN)2 ). 

Since chemiluminescence is a very sensitive method of studying oxidative degradation, it has been used to measure the effect of stress on oxidation of polymers, i.e. stress-induced chemiluminescence (SCL). SCL is by definition a type of triboluminescence, and it is likely that SCL and other forms of tri-boluminescence can occur at the same time. SCL is, however, the only type of tribo-induced luminescence that is oxygen dependent and can therefore be sorted out by measurements in inert and oxidative atmospheres. 

Energy Transfer Processes. Luminescence is a complex sequence of energy transfer processes. Figure 2 is a schematic of the most important of these for photoluminescence, cathodoluminescence, and candoluminescence. The ultimate source of energy is the excitation UV light, electron beam, ion beam, or radical recombination excitation. We are not concerned here about the triggered release of previously trapped energy such as occurs in thermoluminescence and triboluminescence. 

Literature reports of crystal space groups of triboluminescent materials provide evidence for a modest correlation between tribo-luminescence and noncentric space group Q5) of 36 triboluminescent inorganic sulfates (16), 21 are noncentric and 15 are centric of 19 triboluminescent aromatic organic crystals (12) of known crystal structure, 13 are noncentric and 6 are centric. Many compounds crystallize in more than one space group thus the literature crystal structures may not be relevant to the triboluminescent materials. We therefore examined samples from the same batch of crystals for triboluminescence activity and crystal structure. The results are shown in Table II, along with some related compounds (6, 12, 13) whose crystal structures were obtained from the literature. 

The triboluminescence of minerals has been studied visually (see the footnotes to Table I) but only a few minerals have been examined spectroscopically. There are a few clear examples of noncentric crystals, such as quartz, whose emission is lightning, sometimes with black body radiation. Most of the triboluminescent minerals appear to have activity and color which is dependent on impurities, as is the case for kunzite, fluorite, sphalerite and probably the alkali halides. Table I attempts to distinguish between fracto-luminescence and deformation luminescence, but the distinctions are not clear cut. A detailed analysis of the structural features of triboluminescent and nontriboluminescent minerals may make it possible to draw conclusions about the nature and concentration of trace impurities that are not obvious from the color or geological site of the crystals. Triboluminescence could be used as an additional method for characterizing minerals in the field, using only the standard rock hammer, with the sensitive human eye as a detector. 

Triboluminescence Luminescence resulting from the mbbing together of the surface of certain solids. It can be produced, for example, when solids are cmshed. See sonoluminescence. 

Most TL studies are centered on enolate compounds, in particular, rare-earth / -dike-tonates. Present evidence points to morpholinium tetrakis(dibenzoyhnethanato)europate (in) and triethylammonium tetrakis(dibenzoyhnethanato)europate(in) as the first and second most efficient triboluminescent compounds, respectively. In these cases the coexistence of disorder in the chelating ring and the non-centrosymmetric crystal structures may contribute to major charge separation upon cleavage and, consequently, to higher luminescence intensity. 

Other types of luminescence are defined by the source of the energy that causes the light emission. These include chemiluminescence, bioluminescence, electroluminescence, sonoluminescence, triboluminescence, and thermoluminescence. 

Triboluminescence (from the Greek word, tribos, a rubbing) is luminescence that is produced by a mechanical shock to a crystal. It is readily observed in striking or grinding sugar crystals. 

With silicon there are formed the silicide ZrSi2, the natural silicate ZrSiO, and various complex silicates. Native zircon as well as certain other zirconium ores are quite strongly radioactive, and when heated they display luminescence and suffer a change in density and color. Zircon also shows2 the property of triboluminescence. 

The spectrum of the triboluminescence (i.e. emission caused by mechanical stress) of U0a(N03)2,6H20 is similar to that for photo-induced luminescence.167 Possible causes for this effect are electrical excitation (i.e. pressure-induced electrochemiluminescence), intermolecular interactions, and intramolecular deformations. Arguments are presented to show that the third mechanism is not important in this case. Other relevant publications are concerned with electrochemiluminescence of UOa8+ in perchloric acid,168 170 171 173 174 absorption and luminescence spectra of UOa2+ in solution,16 and detailed analyses of the emission spectrum of crystalline UOa2+ salts at low temperatures.170-174... 

Fireflies and many other animals emit radiation by chemiluminescence. In this process, chemicals mix and produce light as one of the products of reaction. Many solids emit light when crushed, a manifestation of triboluminescence. There are no general mechanisms for luminescence, and each type needs to be treated independently. 

The terms Luminescence refers to all other forms of light emission and involves a radiative transition where by a molecule lowers its energy by emission of a photon. In order for the luminescence process to exist for any period of time, energy must be supplied to the system to maintain an excited state population. Different forms of luminescence have been classified based on the source of this energy. While several interesting forms of luminescence exist (eg. Electroluminescence, bioluminescence, radioluminescence, triboluminescence, and sonoluminescence) the type of luminescence, which is of analytical importance is photoluminescence. In photoluminescence the excited state is produced by the absorption of light. 

Luminescence The light emitted by something in response to a stimulus. Specific names are used for different stimuli, e.g., thermoluminescence, optically-stimulated luminescence, photoluminescence, triboluminescence etc. 

Luminescence is the emission of light from excited molecules, ions, or atoms as they relax back to their ground state, which can be further categorized by the mode of excitation. Eor example, in photoluminescence, such as the fluorescence of tonic water, the emitting species is excited by the absorption of light, whereas triboluminescence arises from the structural... 

When comminuting crystalline substances, tri-boluminescence - a special form of luminescence -may be observed, so that the process can be made evident by way of adding triboluminescent substances. 

Habit tetrahedral crystals, granular, coUoform. Color brown, yellow, orange, red, green, or black. Luster resinous, metallic, greasy. Diaphaneity transparent to opaque. Luminescence fluorescent and triboluminescent. Streak brownish white. Geavage 110. Fracture uneven, conchoidal. Twinning 111. Chemical attacked by strong mineral... 

Luminescence includes phenomena such as fluorescence and phosphorescence. It comes from the radiative deactivation of excited matter following an excitation (the mechanism of the excitation, as well as fluorescence and phosphorescence is explained below). The excitation can come from light (photoliuninescence), electricity (electroluminescence), a chemical reaction (chemoluminescence or bioluminescence, if the reaction takes place in a biological system), or a mechanical stress (triboluminescence). We focus on photoluminescence, because most of the other excitation sources require special conditions and are, with the exception of electroluminescence, quite rare, especially when dealing with the luminescence of the lanthanides. 

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