Mechanics and physics of a glass/particles photonic sponge

Abstract

A glass containing mechanoluminescent crystalline particles behaves as a photonic sponge: that is to say it fills up with trapped electrons when exposed to UV light, and it emits light when submitted to a mechanical loading, similar to a sponge soaked with water that is wringed under mechanical action! A major finding of the present study is that the elasto-mechanoluminescence effect showing up on unloading is governed by the deviatoric part of the applied stress (no effect under hydrostatic pressure). Furthermore, the structural source for this phenomenon was elucidated by a detailed density functional theory analysis of the e− energetics at the possible oxygen vacancy sites within the crystalline phase. Both the e− trapping and detrapping processes under load could be explained. An analogy with hydraulic circuits and the rheology of viscoelastic media was successfully introduced to pave the way to a constitutive law for the mechano-optical coupling phenomenon.

Persistent Luminescence in Strontium Aluminate: A Roadmap to a Brighter Future

“…Under such a stress profile, the ML intensity was found to decay with time yet at a rate which is faster than that of the stress‐free persistent luminescence under the same charging conditions. [ 215,219,220,222,223 ] This decaying trend of ML under constant load has been detected in ML phosphors other than SrAl 2 O 4 :Eu 2+ as well, such as (Ba,Ca)TiO 3 :Pr 3+ , [ 224 ] BaSi 2 O 2 N 2 :Eu 2+ , [ 225 ] (Ca,Sr)Al 2 Si 2 O 8 :Eu 2+ ,Pr 3+ , etc. [ 226 ] Furthermore, for a repetitive triangular stress profile, the ML intensity at the maximum stress decreases with increasing cycling number N but can restore to the initial value ( N = 1) after sufficient optical charging.…”

“…Xu et al [201] identified a linear relationship between ML intensity and stress during a ramp. Kim et al [218] confirmed this relation but showed that only the effective stress (namely von Mises stress) contributes to ML, while Dubernet et al [219] argues that hydrostatic stress also causes ML from SrAl 2 O 4 :Eu 2+ particles embedded in a glass matrix. In contrast, Rahimi et al [220] found a quadratic relationship between ML intensity and stress.…”

“…[ 218 ] confirmed this relation but showed that only the effective stress (namely von Mises stress) contributes to ML, while Dubernet et al. [ 219 ] argues that hydrostatic stress also causes ML from SrAl 2 O 4 :Eu 2+ particles embedded in a glass matrix. In contrast, Rahimi et al.…”

“…Subsequently, the model was able to predict the ML response under a more complicated stress profile, including a plateau of constant stress. Under the same theoretical framework, Dubernet et al [219] found that another creep function, borrowed from the Zener model for viscoelasticity, can account for ML intensity under their loading conditions as well. Kim et al [236] simulated the ML from a set of differential equations for electron kinetics among traps and luminescent centers, assuming that the detrapping rate coefficient was proportional to the stress rate.…”

“…Under the same theoretical framework, Dubernet et al. [ 219 ] found that another creep function, borrowed from the Zener model for viscoelasticity, can account for ML intensity under their loading conditions as well. Kim et al.…”