B P Chandra
Articles written in Pramana – Journal of Physics
Volume 8 Issue 5 May 1977 pp 395-401 Solids
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,
Volume 13 Issue 6 December 1979 pp 611-615 Solids
Mechanoluminescence spectra of triglycine sulfate, guanidine aluminium sulfate, rochelle salt, diglycine manganous chloride dihydrate, lithium ammonium tartate monohydrate and potassium dihydrogen phosphate crystals resemble the discharge spectra of nitrogen gases. Glycine silver nitrate, thiourea, ammonium sulfate and azobenzene crystals, the structure of which is centrosymmetric at room temperature, do not show mechanoluminescence. Following the role of crystal structure, the mechanoluminescence excitation is discussed on the basis of the piezo-electrification of the new surfaces created during fracture of the crystals.
Volume 18 Issue 2 February 1982 pp 127-135 Solid State Physics
Crystalloluminescence and temporary mechanoluminescence of As2O3 crystals are investigated. The crystalloluminescence spectra are similar to the photoluminescence and mechanoluminescence (of fresh crystals, in CO2 atmosphere) spectra. The mechanoluminescence spectra of freshly grown crystals taken in air consist of the superposition of the photoluminescence and nitrogen emissions. The mechanoluminescence spectra of old crystals of As2O3 consist of only the nitrogen emission. The total number of crystalloluminescence flashes is linearly related to the total mass of the crystals grown. The mechanoluminescence intensity increases with the mass of the crystals. The mechanoluminescence intensity decreases with the age of the crystals and the rate of decrease increases with increasing temperature of the crystals. Different possibilities of crystalloluminescence and mechanoluminescence excitations in As2O3 crystals are explored and it is concluded that crystalloluminescence and mechanoluminescence are of different origins.
Volume 19 Issue 5 November 1982 pp 455-465 Solid State Physics
The mechanoluminescence spectra of (Zn, Cd)S phosphors shift towards shorter wavelength side as compared to the photoluminescence spectra, however, the photoluminescence spectra shift towards shorter wavelength side with increasing pressure with less pressure coefficient. This finding eliminates the thermal population mechanism and suggests the electrical excitation mechanism for the mechanoluminescence excitation. The decay of mechanoluminescence after the deformation (Zn, Cd)S phosphors may be controlled by the recombination rate of holes and electrons, i.e. by the finite times required for the liberation of the electrons from the traps and for the electron transport, and consequently the decay of mechanoluminescence may be similar to the decay of photoluminescence.
Volume 21 Issue 3 September 1983 pp 159-169 Solid State Physics
The gamma-irradiated KCl crystals exhibit mechanoluminescence during elastic, plastic and fracture deformation. The mechanoluminiscence (
Volume 25 Issue 6 December 1985 pp 723-731 Liquids
The mechanoluminescence (
Volume 29 Issue 4 October 1987 pp 399-407 Condensed Matter Physics
Intense and unique type of mechanoluminescence (ML) is found in tetrahedral manganese (II) complexes. During the excitation of ML by the impact of a piston onto the crystal, the ML intensity initially increases with time, attains a maximum value and then decreases. After retardation of the piston, the decay rate of ML is faster during crystal deformation; however, its value decreases after cessation of the deformation and becomes equal to the decay rate of phosphorescence. The ML disappears below the melting point. Since the crystals of tetrahedral manganese (II) complexes are centrosymmetric, the local non-centrosymmetric sites near the defects are attributed to be responsible for the mechanoluminescence excitation.
Volume 36 Issue 4 April 1991 pp 407-421 Research Articles
During the process of deforming a crystal, a high pressure is developed near the tip of mobile cracks, which may in turn produce a new ground state by thermal electron transfer. Upon sudden release of pressure, the electron can either relax to one atmosphere ground state or remain in the excited state potential well long enough to relax to one atmosphere and radiatively transfer back to the ground state. For analysing the pressure induced thermal population of the excited state, the mechanoluminescence(ML) and high pressure photoluminescence(PL) of several organic and inorganic crystals were measured. The study indicated that usual pressure coefficient of energy shift of the order of 50–100 cm−1/kbar and the stress at the crack-tip of the order of 5–10 kbar, are not sufficient to cause the thermal population of the excited state. If by any means the product of pressure coefficient and stress at the mobile crack-tip can be increased by 50 to 100 times, then the thermal population of the excited states may take place. Using the pressure coefficient of energy shift and the difference in ML and PL spectra, and using independently the change in relative intensities of the vibronic peaks, the pressure at the emitting mechanoluminescent crystal sites is evaluated and it is found to be of the order of several kbar which varies from crystal to crystal.
Volume 46 Issue 2 February 1996 pp 127-143
A theoretical study is made on the mobile interstitial and mobile electron models of mechano-induced luminescence in coloured alkali halide crystals. Equations derived indicate that the mechanoluminescence intensity should depend on several factors like strain rate, applied stress, temperature, density of F-centres and volume of crystal. The equations also involve the efficiency and decay time of mechanoluminescence. Results of mobile interstitial and mobile electron models are compared with the experimental observations, which indicated that the latter is more suitable as compared to the former. From the temperature dependence of ML, the energy gaps between the dislocation band and ground state of F-centre is calculated which are 0.08, 0.072 and 0.09 eV for KCl, KBr and NaCl crystals, respectively. The theory predicts that the decay of ML intensity is related to the process of stress relaxation in crystals.
Volume 48 Issue 6 June 1997 pp 1135-1143
A new field emission theory of dislocation-sensitized photo-stimulated exo-electron emission (DSPEE) is proposed, which shows that the increase in the intensity of photo emission from
Volume 54 Issue 2 February 2000 pp 287-303 Research Articles
The present paper reports the correlation between deformation bleaching of coloration and mechanoluminescence (ML) in coloured alkali halide crystals. When the
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