Triboluminescence in sodium chloride

The emission of light due to rubbing or impact of two surfaces (Triboluminescence) has been traditionally studied under visible and ultraviolet spectrum. The current study provides an experimental insight into infrared emission occurring during low velocity impact on common salt crystals. The high speed IR imaging done using a whole field IR camera is first of its kind of measurement that provides experimental verification of IR emission occurring in these events. It was observed that the nature of impact surface and the crystalline structure of the material have a marked role in the IR emission. Of the existing theories that explain the origin of light emission in TL, the model provided by Chapman, that TL is a thermal radiation from high temperature regions, which propagate along with the crack, matches closely with the current experimental observations.     

Triboluminescence of nitrate crystals

Triboluminescence (TL) is studied in 22 crystals of common inorganic nitrates. With the exception of Zn(NO₃)₂·6H₂O all of the non-centrosymmetric crystals are triboluminescent and all the crystals which do not exhibit TL are centrosymmetric. The TL spectrum of (UO₂)(NO₃)₂·6H₂O crystals shows that the emission originates from both the uranyl ion and from nitrogen. The TL of the other crystals originates from excited states of nitrogen. TL appears concurrently with the sudden force decrease in the fracture region of the force vs compression curve of the crystals. The motion of cracks and thereby the creation of new surfaces is responsible for the excitation of TL. The mechanisms of the TL excitation in piezoelectric and non-piezoelectric crystals are discussed.     

Triboluminescence in tartrate crystals and simultaneous charge produced at fracture

The variation of triboluminescence intensity in tartaric acid, sodium tartrate, rochelle salt, dipotassium tartrate and ammonium tartrate crystals with the simultaneous charge produced at fracture has been studied. It is found that for the crystals of a given mass, the triboluminescence intensity and the simultaneous charge produced at fracture increase with crushing mass and both of them attain saturation values after particular values of crushing mass, for a given crushing height. The saturation value of the TL intensity increases, but the charge produced at fracture due to shock induced polarization decreases with increase of the crushing height. The TL is higher for those tartrate crystals which develop less charge at fracture. It has been concluded that in impulsive crushing, elastic stress in crystal increases due to the reduction of piezoelectric stress. Hence at higher values of the elastic stress, the moving dislocations are able to interact with more luminescent centres, due to which the TL intensity increases.Thanks are due to the Principal, Government College of Science, Raipur (M.P.) India, for providing the necessary facilities. One of the authors (B.P.C.) is also thankful to C.S.I.R., New Delhi, for the award of a Senior Research Fellowship.     

Triboluminescence,a new tool to investigate fracture-initiation time of crystals under stress

The present paper reports that triboluminescence (TBL) does not appear at the instant of impact of the load but a certain time lag is required for its appearance which depends on the value of the stress applied to the crystal. Since TBL appears in sugar crystals during the creation of new surfaces, the fracture-initiation time of the crystal has been taken to be the delay time in observing TBL pulse after the application of stress. The dependence of fracture-initiation time,t _f ^σ , of crystals on the stress, σ, may be expressed ast _f ^σ =t _o exp (− ασ), wheret _o and α are constants. The values of the lattice energy, and the change in lattice energy per unit stress, of sugar crystals have been calculated from TBL measurements and they have been found to be 21·2 kcal mole⁻¹ and 0·41 × 10⁻⁸ kcal mole⁻¹ dyne⁻¹ cm² respectively.     

Triboluminescence and the mechanism of discharge of gases between the newly-created surfaces of crystals during their fracture

The present paper reports on the mechanism of discharge of the gases between the newly-created surfaces of sugar, tartaric acid and six other crystals during their fracture. It has been shown that the TBL intensity obtained by crushing the crystals inside ths liquid, anhydrous diethylether, diminishes more considerably than when they are crushed in air but it depends on the mode of mechanical crushing in the same manner as the TBL intensity obtained by crushing the crystals in air does. The TBL intensity obtained by crushing the crystal inside the liquid is higher for those crystals which show higher TBL when crushed in air. It has been concluded that some part of TBL is due to the excitation of the TBL centres and the remaining part to the discharge of the gases between the newly-created surfaces, to the exo-emission of the electrons from the TBL centres at the instant of fracture of the crystal.Thanks are due to Dr. J. N.Das, Professor and Head of the Physics Department, Government Science College, Raipur (M. P.) India for his guidance and help. The author also wishes to thank the Director-General, C. S. I. R. New Delhi, for the award of a Post-Doctoral Fellowship during the tenure of the work.     

Crystal Structure,Luminescence, and Triboluminescence of the Complex [Eu2(Quin)42H2O2Dipy]2(NO3)2H2O

Optics and Spectroscopy - An atomic structure of crystals of the complex [Eu2(Quin)42Н2O2Dipy]2 · 2(NO3) · Н2O, (Quin, anion of quinaldic acid; Dipy, 2,2'-dipyridyl),...