Mechanoluminescence of Nanoparticles

Abstract

Certain nanoparticles exhibit intense light emission during their elastic deformation, called the phenomenon of elastico mechanoluminescence (EML).When ZnS:Mn and SrAl2O4:Eu nanoparticles are deformed in the elastic region by the stress initially increasing with time and then attaining a fixed value or by the stress initially increasing and then decreasing with time or by the impact stress, then after a threshold pressure, initially the EML intensity increases with time, attains a maximum value and later on it decreases with time. For the fixed pressure or slowly decreasing pressure, the slow decay time of EML is equal to the lifetime of electrons in the shallow traps lying in the normal piezoelectric region of the crystals.In these cases, sometimes, fast decay of EML also appears and it is related to the machine -constant, that is, the decay time of strain- rate after the power to the cross-head of the machine is switched off. For the fast-deformation caused by impact stress, the fast decay time of EML is controlled by the rise time of impact stress, and the slow decay of EML gives the lifetime of retrapped electrons in the shallow traps. For ZnS:Mn and SrAl2O4:Eu nanoparticles, the total EML intensity increases quadratically with the applied pressure. The diminished EML intensity of SrAl2O4:Eu nanoparticles caused by number of pressings can be recovered by exposing the sample to UV-radiation. The tribo ML of ZnS:Mn nanoparticles increases with increasing value of the load placed on the rotating rod inducing tribo ML. The EML spectra of ZnS:Mn and SrAl2O4:Eu nanoparticles are similar to their photoluminescence and electrolumi- nescence spectra. The piezoelectrically-induced detrapping model is found to be suitable for the EML of nanoparticles and the expressions derived on the basis of this model are able to explain successfully the characteristics of the EML of nanoparticles. The EML of nanoparticles has been found useful in stress sensor and an EML-based safety-management monitoring system has been developed. The EML of nanoparticles can be used for the visualizations of stress distribution in solids, stress field near crack-tip, quasidynamic crack-propagation in solids and internal defect in a pipe. The EML intensity of nanoparticles is so intense that it is able to drive a solar cell system and it can be used as a light-source for specific applications. Furthermore, several parameters of nanoparticles can be determined from their EML measurements.