Dynamics of the mechanoluminescence induced by elastic deformation of persistent luminescent crystals
Dynamics of the mechanoluminescence induced by elastic deformation of persistent luminescent crystals
复制标题
DOI：
10.1016/j.jlumin.2011.09.054
复制
发表时间：
2012-03-01
影响因子：
3.6
通讯作者：
Chandra, B. P.
中科院分区：
文献类型：
--
作者：
Chandra, V. K.;Chandra, B. P.
当在环氧树脂中混合微晶或纳米晶永久发光材料形成的合适尺寸的复合材料以固定的压缩速率变形时，弹性机械发光(EML)发射在阈值压力后发生，其中EML强度随着施加压力的线性增加而增加。当外加压力保持不变或线性减小时，电磁脉冲强度随时间而减小，在这种情况下，电磁脉冲强度最初以较快的速度减小，然后以较慢的速度减小，或者有时只有一个衰减时间以指数形式减小。当一个小球从较低的高度落到永久发光材料的薄膜上时，EML强度最初随时间增加，达到峰值，然后开始以较快的速度下降，后来以较慢的速度下降。在这种情况下，峰值EML强度和总EML强度都随着球落到胶片上的高度线性增加。考虑基于指数分布陷阱逐次退陷的压电致退陷模型，对永久发光晶体和薄膜弹性形变引起的发光动力学进行了理论分析。结果表明，EML的强度与压力、压缩速率或应变速率、温度、填充电子陷阱密度、缺陷中心附近的压电常数等参数有关，在慢变形和冲击应力的情况下，快衰减时间与样品压缩速率降低的时间常数有关，而EML的慢衰减时间与晶体正常压电区浅陷阱中电子的寿命有关。在压力释放过程中产生的EML和在连续加压过程中产生的EML都是由于在激活剂离子附近的空置电子陷阱中重新捕获电子而发生的，其中重新捕获是由位于晶体正常压电区的填充的浅陷阱热释放的电子引起的，这些浅陷阱在压力增加时在稳定陷阱的脱陷过程中被填充。在该模型的基础上，可以很好地理解电磁致发射强度与不同参数的依赖关系、电磁致发光动力学和阈值压力、特征脱陷压电场、形变脱陷系数、某些晶体高压下电磁致发光强度的非线性增加以及具有较高形变脱陷系数的晶体中较高的电磁致发光强度等物理概念。理论计算结果与实验结果吻合较好。结果表明，本研究有助于制作具有较长持续时间的强持久弹性机械发光材料。(C)2011爱思唯尔B.V.保留所有权利。
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. (C) 2011 Elsevier B.V. All rights reserved.