Cleavage Mechanoluminescence in Crystals

Abstract

When a crystal is cleaved, initially the mechanoluminescence (ML) intensity increases linearly with time, attains an optimum‐value Im at a particular value of timetm, and then decays exponentially with time. Cleavage ML provides a new tool to determine the velocity, v of cracks in crystals, and it may be given by v = H/tm, where H is the thickness of the crystal. Both, the peak ML intensity Im and total ML intensity IT increase linearly with the area of newly created surfaces A as well as with the surface charge density γ. The ML intensity decreases with temperature primarily due to the decrease in the surface charge density. Beyond a particular temperature, the surface charge density may decrease to such a value where the breakdown of gases and solids may not be possible and thereby the ML may not appear. Depending on the prevailing conditions either the ML emission resembling gas discharge or other types of the luminescence of solids, or that having these two characters may be obtained. There exists a good correlation between the theoretical and experimental results obtained for cleavage ML in crystals.

Trap-controlled mechanoluminescent materials

“…1) [2]. Correspondingly, applications of fractoluminescent materials are limited to real-time sensing of structural damage in the target structure [43][44][45][46][47][48][49][50][51][52][53][54][55][56]. Fractoluminescence is not discussed in any detail in this review and the reader is directed to the following articles and reviews for further information [57][58][59][60][61][62][63].…”

Transient behaviour of the mechanoluminescence induced by impulsive deformation of fluorescent and phosphorescent crystals

“…The ML decay time of tartaric acid under compression has been reported to be 0.3 ms [7], but under cleavage with better detector time resolution, it has been found to be 20 ms [8]. In air, the lifetimes for the ML of alkali halides after cleavage have been found to be 4 ms [1], but after grinding the lifetimes were 3 and 60 h [9].…”

“…So far as the ML resembling photoluminescence is concerned, after fracture in air, coumarin, triphenylamine, phenanthrene and uranyl nitrate hexahydrate exhibit lifetimes in the range of 25-50 ms, that are not very different from that of the gas discharge ML [8]. These lifetimes are much longer than the PL lifetimes of these crystals, and as such, the time-evolution of their ML may be able to provide information about their deformation and fracture on nanosecond time scales.…”

Triboluminescence and crystal structure of the centrosymmetric complex [Tb(NO3)2(Acac)(Phen)2]·H2O

“…)-C(10)-C(11) 117.6(1) C(9)-C(10)-C(12) 122.8(1) C(11)-C(10)-C(12) 119.6(1) N(2)-C(11)-C(10) 122.7(1) O(4)-C(13)-C(14) 124.9(1) O(4)-C(13)-C(15) 116.0(1) C(14)-C(13)-C(15) 119.2(1)…”