https://escholarship.org/content/qt7x21z1gr/qt7x21z1gr.pdf?t=ptp6hu

Trap-controlled mechanoluminescent materials

Mechanoluminescence (ML) is a type of luminescence induced by any mechanical action on solids. The light emissions induced by elastic deformation, plastic deformation and fracture of solids are called elastico ML (EML), plastico ML (PML) and fracto ML (FML), respectively. Whereas nearly 50% of all organic molecular solids and inorganic salts exhibit FML, only a few solids exhibit EML and PML. The EML and FML of certain solids are so intense that they can be seen during daylight with the naked eye. Mechanolumnescence has a great potential for use in different types of mechano-optical devices such as stress sensors, damage sensors, impact sensors, fracture sensors and safety management monitoring systems. This article reports a survey of the literature from 1605 to 2013. Mechanoluminescence is studied by physicists, chemists, material scientists, geologists, medical scientists, engineers and technologists, among others and researchers will certainly benefit from the literature survey on ML given here. In addition, the field of mechanoluminescence may attract the interest of many new researchers.

Survey of the literature on mechanoluminescence from 1605 to 2013.

The mechanical characteristics of triboluminescence (TL) from coumarin, acenaphthene, resorcinol, phenanthrene, and m‐aminophenol crystals are studied. The TL spectra of these crystals resemble their fluorescence spectra. The TL appears concurrently with the sudden force decreases in the fracture regions of the force vs compression curves of the crystals. The decay time of TL from the motion of a single crack is of the order of a microsecond. The dependence of the TL intensity on time, impact velocity, the applied stress, and the crystal dimensions is discussed quantitatively using a phenomenological theory based on the movement and interaction of cracks in the crystals. No systematic correlation of the normalized TL intensity with the photoluminescence efficiency, charge produced during crystal fracture, or the experimental fracture stress is found. No considerable differences are found between the TL intensities of crystals grown in argon and in nitrogen atmospheres when they are crushed inside argon‐stripped liquid or in air. Triboluminescence is an intrinsic property of the crystals and is discussed in terms of the piezoelectrification produced during the movement of cracks in the crystals.

Mechanical characteristics and mechanism of the triboluminescence of fluorescent molecular crystals

The present paper reports the real-time sensing of the amplitude and duration of impact stress using mechanoluminescence (ML) of the films such as ZnS:Mn and SrAl2O4:Eu. After the impact of a small ball from a low height onto the film, initially the elastico mechanoluminescence (EML) intensity increases with time, attains a peak value and then it decreases with time, initially at a fast rate and later on at a slow rate. The fast decay time of the EML intensity is related to the rate constant for the rise of impact stress and 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, which get filled during the detrapping of thermally stable traps at the time of the increase of pressure. Both the peaks of EML intensity and total EML intensity increase linearly with the height through which the ball is dropped onto the films. The EML spectra are similar to the corresponding photoluminescence and electroluminescence spectra. On the basis of the localized piezoelectrically induced electron detrapping model, expressions are derived for different parameters of the impact stress-induced EML of the films, whereby a good agreement is found between the experimental and theoretical results. As the EML intensity depends on the impact stress, the impact stress can be sensed by measuring the EML intensity. Furthermore, the duration of stress is related to the time tm corresponding to the peak of the EML intensity versus time curve; hence, the pulse duration of the impact stress can be monitored by measuring the value of time tm.

Real-time mechanoluminescence sensing of the amplitude and duration of impact stress

Dynamics of the mechanoluminescence induced by elastic deformation of persistent luminescent crystals

The author describes the triboluminescence of rubber and demonstrates it by records of the intensity of emitted light and the variation of strain with stress of a rubber band. The marked increase of the emission of light with onset of plastic deformation and the irreversibility of triboluminescence on repeated deformation suggest an analogy between triboluminescence and acoustic emission. These properties of triboluminescence, it is suggested, may be applied like sound emission in non-destructive testing.

I. Grabec

Papers

Analogy between triboluminescence of rubber and acoustic emission in metals