Mechanoluminescence of Halides and Other Inorganic Crystals

Abstract

Mechanoluminescence is studied in halides and other inorganic crystals. All the non‐centrosymmetric crystals are mechanoluminescent and all the crystals which do not exhibit mechanoluminescence are centrosymmetric. Certain centrosymmetric crystals also exhibit ML which is comparable in intensity to that of the non‐centrosymmetric crystals. The mechanoluminescence spectra of the crystals are reported. The mechanoluminescence spectra of Cs2[Pt(CN)4] · H2O crystals shift towards higher wavelengths as compared to the photoluminescence spectra. The ML activity per mole of the crystals spans four orders of magnitude. Among the alkali halides generally the harder crystals exhibit ML. The correlation of mechanoluminescence with the hardness of the crystals and the earlier disappearance of mechanoluminescence with increasing temperature suggest that the separation of the charged surfaces during the fracture of the crystals should be responsible for the mechanoluminescence excitation. The appearance or non‐appearance of mechanoluminescence in centrosymmetric alkali halide crystals may be attributed to the respective ability or inability of cracks to pass through the charged directions of the misoriented regions.

Triboluminescence with and without Air

“…Qualitatively, the hardest materials in this study are 1 and 15 , but the triboluminescence of 1 is quenched by liquids. High crack propagation rates might be needed to develop adequate potential for discharge triboluminescence, as hard materials have been shown to exhibit more intense triboluminescence than similar softer materials . Dissipation of crack energy into modes other than charge separation might be responsible for the observed differences in rate, but the possibility that a discharge is not necessary must be retained for those materials whose triboluminescence is not quenched.…”

Survey of the literature on mechanoluminescence from 1605 to 2013

“…In the 17th century, only five papers were published on ML ; in the 18th century, 15 papers were published ; in the 19th century, 19 papers were published ; in the 20th century, ~ 372 papers were published …”

Mechanoluminescence

“…Wolff et al (1952) compiled a list of about 450 ML crystals including inorganic compounds, minerals, and aliphatic and aromatic organic compounds. Chandra and his co-workers reported the spectroscopy, intensity, and crystal structure-ML correlation of some 400 organic and inorganic crystals (Chandra and Elyas, 1979;Chandra and Shrivastava, 1979;Chandra et al, 1980;Chandra and Verma, 1980;Chandra, 1981Chandra, , 1985Chandra and Tutakne, 1981;Chandra and Zink, 1980a,b,c, 1981aChandra et al, 1982a).…”