The paper reports that the mechanoluminescence (ML) is not an inherent property of only the non-centrosymmetric crystals. The ML may appear in number of centrosymmetric crystals due to variety of processes. The ML of 82 centrosymmetric crystals are reported and different models are proposed for the ML excitation. The models proposed are: space charge electrificaiton model, triboelectrification model, phase transformation model, gas adsorption model, chemical reaction model, thermal population model, molecular deformation model, cleavage electrification model, defective piezoelectric phase model, dislocation defect stripping model, dislocation unpinning model, dislocation annihilation model, charged dislocation model and incandecent light emission model. It is shown that on the basis of the proposed model, intense mechanoluminescent materials with desired nature and characteristics may be prepared.

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.

The present paper reports the crystalloluminescence (CRL) produced during the polymorphic phase transition of growing crystallites and models the dynamics of the process. The CRL emission may take place during the polymorphic phase transition of crystals due to several processes such as production of micro-fracture of crystallites during the phase transition, thermal population in the over-strained sites and electronic excitation by the energy released during the phase transition. Considering the basic concepts of crystallization from the supersaturation solution, expressions are derived which are able to explain satisfactorily the temporal, thermal, spectral, concentration and other characteristics of the CRL. It is shown that the induction period for crystal nucleation, and the lifetime of supersaturation, may be determined from the CRL measurements.

The present paper reports the mechanoluminescence (ML) produced during fracture of metals. The mechanism of ML in metals is based on the generation of holes during the decay of mobile dislocations on the surface and subsequent electron-hole radiative recombination. The following equation is derived for the transient ML intensity of the fracto-induced ML in metals The spectroscopy of ML in metals is also discussed. A good correlation is found between the theoretical and experimentals results.

Manganese doped cobalt nano ferrites were synthesized by co-precipitation method having general formula Co1-xMnxFe2O4 (x =0.0-1.0). These materials are studied to analyze the structural effects on the associated materials properties. The prepared samples were heat treated at 7500 C for two hours. Sintering effect on the structural properties was investigated. The lattice constants of samples were measured from X-rays diffraction data. The (311) peak was used to find crystallites size by the Scherrer formula. Structural morphology was observed by scanning electron microscopy. Variation with temperature in electrical resistivity (DC) and drift mobility were also investigated. The variations with frequency and composition in AC electrical properties of prepared samples were determined. The structural and electrical properties demonstrated firm association. Saturation magnetization, coercivity and remanence of the samples were discussed with the help of sharing of cations within crystals.