科研之友
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摘要
When a composite of suitable dimension formed by mixing the microcrystalline or nanocrystalline persistent luminescent materials in epoxy resin is deformed at a fixed pressing rate, then the elastico mechanoluminescence (EML) emission takes place after a threshold pressure, in which the EML intensity increases linearly with the applied pressure. When the applied pressure is kept constant or decreased linearly, then the EML intensity decreases with time, in which depending on the prevailing condition, the EML intensity initially decreases at a fast rate and then at a slow rate or sometimes it decreases exponentially having only one decay time. When a small ball is dropped from a low height onto the film of a persistent luminescent material, then initially the EML intensity increases with time, attains a peak value and then it decreases initially at a fast rate and later on at a slow rate. In this case, both the peak EML intensity and the total EML intensity increase linearly with the height through which the ball is dropped onto the film. Considering the piezoelectrically induced detrapping model based on successive detrapping of exponentially distributed traps a theoretical approach is made to the dynamics of light emission induced by elastic deformation of persistent luminescent crystals and thin films. It is shown that the EML intensity depends on several parameters such as pressure, pressing rate or strain rate, temperature, density of filled electron traps, piezoelectric constant near defect centers, etc. Both, in the case of slow deformation and impact stress, the fast decay time is related to the time-constant for the decrease of pressing rate of the samples and the slow decay time of EML is related to the lifetime of electrons in the shallow traps lying in the normal piezoelectric region of the crystals. Both, the EML produced during the release of pressure and the EML produced during the successive applications of pressure take place due to the detrapping of retrapped electrons in the vacant electron traps near activator ions, in which retrapping is caused by the thermally released electrons from the filled shallow traps lying in the normal piezoelectric region of the crystals, which get filled during the detrapping of stable traps at the time of increase of pressure. On the basis of the proposed model, the dependence of EML intensity on different parameters, dynamics of EML and physical concepts of the threshold pressure, characteristic piezoelectric field for detrapping, coefficient of deformation detrapping, nonlinear increase of the EML intensity of some crystals at high pressure and higher EML intensity in the crystals having higher coefficient of deformation detrapping can be satisfactorily understood. A good agreement is found between the theoretical and experimental results. It is shown that the present study may be helpful in tailoring the intense persistent elastico mechanoluminescent materials having long lasting time.
- 出版日期2012-3
