Deformation luminescence

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. 

Lighting. An important appHcation of clear fused quartz is as envelop material for mercury vapor lamps (228). In addition to resistance to deformation at operating temperatures and pressures, fused quartz offers ultraviolet transmission to permit color correction. Color is corrected by coating the iaside of the outer envelope of the mercury vapor lamp with phosphor (see Luminescent materials). Ultraviolet light from the arc passes through the fused quartz envelope and excites the phosphor, produciag a color nearer the red end of the spectmm (229). A more recent improvement is the iacorporation of metal haHdes ia the lamp (230,231). 

The promise of luminescent methodology is based on many types of information that can be derived from mineralogical samples. These include RE from Ce to Yb, identities down to the ppb range, the valence states of the RE, the nature of the sites at which RE reside and the ways of compensating the charge, and features related to the presence of other ions (donors, activators). All this information can be used to determine the chemical, thermal, and deformational history of the material. 

Knowledge of the sample pressure is essential in all high-pressure experiments. It is vital for determinations of equations of state, for comparisons with other experimental studies and for comparisons with theoretical calculations. Unfortunately, one cannot determine the sample pressure directly from the applied force on the anvils and their cross-sectional area, as losses due to friction and elastic deformation cannot be accurately accounted for. While an absolute pressure scale can be obtained from the volume and compressibility, by integration of the bulk modulus [109], the most commonly-employed methods to determine pressures in crystallographic experiments are to use a luminescent pressure sensor, or the known equation of state of a calibrant placed into the sample chamber with the sample. W.B. Holzapfel has recently reviewed both fluorescence and calibrant data with the aim of realising a practical pressure scale to 300 GPa [138]. 

Crystal-field spectroscopy of dn ions is being extended nowadays to the near-infrared region with interesting results. Vibronic structure is nowadays used to obtain information on the deformation of the excited state. Also in case of the closed-shell d° complexes the excited state appears to be strongly distorted. Among the latter class especially the linear species show efficient luminescence. Molecular-orbital calculations are in progress and will probably yield interesting results. 

The theory of relaxation spectra in polarized luminescence for various dynamic models of a flexible polymer chain has been developed by several groups of workers. Wahl has proposed a theory for the model of Gaussian subchains. The authors and coworkers used dynamic chain models consisting of rigid or deformable elements with continuous visco-elastic mechanism of mobility and rotational-isomeric lattice chain... 

When the fluorescence method becomes more generally adopted, it will be necessary to study not only those factors (neutral salt, temperature) which alter the equilibrium relationships, but also those which influence fluorescence (deformation effect, influence of solvent, etc. cf. P. W. Danckwortt, Luminescence Analysis, 2 Ed., Leipzig 1929 F. Weigebt, Optical Methods in Chemistry, 1927). The interesting publication of L. J. Desha should be consulted regarding the quantitative aspects of fluorometry. In quantitative work it is best to use the filtered monochromatic ultraviolet radiation (X = 366 mm) from a quartz lamp. Con-... 

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... 

Sprunt et al. (1978) have studied the cathodoluminescence of two sequences of naturally deformed quartzites. They found that metamorphism appears to homogenize the luminescences and that the color is related to the metamorphic grade, with low temperature causing red luminescence and high temperature causing blue luminescence. They also stated that strain is a factor in the cathodoluminescence of quartz. 

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