M.L. & A.I. Lab.

What is the mechano-luminescence ?

Stress (or strain) induced light emitting materials have a long history and have been defined as fracto-, tribo-, piezo- mechano- or elastico-luminescence. Basically, this phenomenon can be categorized in the first place according to whether the fracture is accompanied with luminescence or not. The fracture involved process is called fracto- or tribo- luminescence, the origin of which is due to the plasma discharge in the air surrounding the fractured surface. A great number of organic and inorganic materials exhibit fracto- or tribo- luminescence. Sticky tape also emitted this type of luminescence as it unpeels. A prominent improvement of light emission in this category was achieved and the applicability for industrial use as a sensing device has been growing. However, the use of the fracture-involved process has a limitation in terms of reproducibility. On the other hand, the other type of stress (or strain) induced luminescence, so called piezo- or elastico-luminescence, has a better applicability to reproducible sensing systems by the fact that it operates in the elastic range without failure of the material. Some Alkali halide crystals were representative piezo-or elastico-luminescent materials. For convenience sake, this type of process has been referred to as simply ‘mechano-luminescence (ML)’.

Our Research Progress Shows !

The ML, which is light emission resulting from any mechanical actions, such as tension, compression, friction, and fracture, on a solid, have made possible the direct observations of the crack tip stress field, visualization of quasi-dynamic crack propagation and bridging stress in a range of ceramics, and a pulsed laser deposition (PLD) coatings or mechano-luminescent paints as an artificial skin to sense mechanical stress by visible light emission. Meanwhile, the rate-equation model for the loading-rate-dependent mechano-luminescence and the cyclic second harmonic phenomenon of SrAl₂O₄:Eu²⁺,Dy³⁺ (SAO) which are helpful for understanding mechanics of ML, have also been established.

Recently, the efforts to establish new standard testing method for measuring the fracture toughness and torque rate under various stress modes or new non-destructive monitoring method for various mega structure by using ML technology are now in progress.