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Recently we demonstrated that CaAl2Si2O8: Eu2+ showed novel strong mechanoluminescence (ML). In order to improve the mechanoluminescence intensity, we partly substituted the Ca2+ ions by Sr2+ ions. It was found that the ML intensity was enhanced about three times as great as the one of CaAl2Si2O8: Eu2+ by substituting 40% of Ca2+ ions to Sr2+ ions. Furthermore it was revealed that the main peaks in XRD pattern shifted to lower angle side and the emission peak shifted to a short wavelength from 428 to 418 nm, indicating that the substitution resulted in the cell volume expansion and the change of luminescent color. Based on the results of thermoluminescence and electroluminescence measurements, the possible mechanisms for the improvement of ML intensity were proposed.

Highly oriented SrAl2O4:Eu film had been deposited on a quartz glass using the RF sputtering method. The fabricated film displayed fiber-texture with the (031) orientation. The surface of the film was smooth and compact. In addition, under the UV excitation, the film emitted green light. After the removal of UV excitation, a long afterglow phenomenon could be observed from this film. The important point of this study was that SAOE film displays strong adhesion and high green triboluminescence (Tribo-L). Such properties made the films be a potential candidate as stress indicators.

We have demonstrated a novel blue-violet emitting mechanoluminscent(ML) material with calcium aluminosilicate(CaAl2Si2O8:Eu2+). The ML was clearly visible to the naked eye in the atmosphere and showed a similar spectrum to photoluminescence with a peak at 430nm. In order to enhance the ML intensity, various rare earth ions were selected as co-dopants including La, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. It was found that the intensity of ML was strongly dependent on the kinds of the codoped rare earth ion, especially the co-doping of Ho3+ was found to greatly enhance the ML intensity. From the results of thermoluminescence(ThL) measurements, the enhancement of the ML intensity was closely related with the filled trap concentration and trap depth.

SrAl2O4:Eu films on an inconel 600 substrate with good adhesion were successfully prepared by the radio frequency sputtering method. The crystallinity and surface morphology of the SrAl2O4:Eu films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and atomic force microscope (AFM). The films exhibited an intensively green photoluminescence (PL) and high triboluminescence (Tribo-L) intensity.

We have discovered that Sr2MgSi2O7:Eu, SrCaMgSi2O7:Eu and Ca2MgSi2O7:Eu phosphors emit blue, blue-greenish and green light under the application of a mechanical stress respectively, called as mechanoluminescence (ML). The ML showed a similar spectrum as photoluminescence (PL), which indicated that ML is emitted from the same center of Eu2+ ions as PL. Such bright lights of ML emission can be observed by the naked eye when pressing these samples.

We successfully synthesized the novel mechanoluminescent material ZnS:Mn,Te with a wurtzite structure by controlling the pH of the solution used in the wet process. This material showed a distinct red mechanoluminescence (ML) with an increased intensity, being one order of magnitude higher than that of the sample prepared using a solid-state reaction. This marked increase in ML intensity was realized by eliminating ZnO and MnO impurities.

Europium-doped strontium aluminate is a famous green phosphor that can give luminescence under a mechanical stress that is named elastico-luminescence. This paper reports a modified reverse micelles process for preparing the europium-doped strontium aluminate nanoparticles. A polymeric matrix was coated on the surface of the precursor formed in the reverse micelles. The polymeric matrix is considered to prevent the particle agglomeration by forming a carbon layer while the precursor was heat-treated. Consequently, the luminescent nanoparticles were achieved after removing the carbon layer and forming the luminescent center under a reducing atmosphere. The processing and properties of the luminescent nanoparticles were discussed in this paper.

We have successfully demonstrated that the stress distribution of a metal substrate can be directly displayed by coating SrAl2O4:Eu (SAO), a representative of strong mechanoluminescent materials, on the surface of test objects. An aluminum plate with SAO sensing film had been applied to experimental analysis of stress concentrations, and a numerical calculation via a finite element method confirmed that the observed real time mechanoluminescence images displayed the stress distribution. As a result, visualization of stress distribution on metal surface has been realized by ML images using SAO sensing film, and this novel visualization technique can be applied for viewing the stress concentration in various fields such as modeling, manufacturing and demonstration of an industrial product.

We have revealed that SrCaMgSi2O7:Eu phosphors emits blue-greenish light under the application of a mechanical stress, called as mechanoluminescence (ML). The ML showed a similar spectrum as photoluminescence, which indicated that ML is emitted from the same center of Eu2+ ions as PL. Such a blue-greenish light of ML emission can be seen by the naked eye when pressing the sample. In addition, the ML intensity of SrCaMgSi2O7:Eu proportionally increased with the increase of mechanical load.

The influence of pre-deposition of homo-buffer layers on film quality is studied for SrAl2O4:Eu2+ (SAO) crystalline film prepared by RF magnetron method. This preparation technique is necessary to prepare high quality films suitable for the development of SAO devices. Crystallinity and surface morphology were characterized by X-ray diffraction and scanning electron microscopy. After introducing a homo-buffer layer, not only the crystalline but also the surface morphology and adhesion of the film were obviously improved. These results imply that the buffer layer relaxes the strain due to the lattice mismatch between SAO and quartz glass, which improved the crystalline and adhesion of the film.

Strongly adherent SrAl2O4:Eu films were fabricated on the rough surface of an alumina substrate by a combination of the RF magnetron sputtering technique and a post-annealing treatment. A crystalline SrAl2O4:Eu2+ film was achieved after annealing at 1000°C in reduced atmosphere and it exhibit a intensively green PL and triboluminescence (TL) while an as-deposition film showed the amorphous state and weakly red photoluminescence (PL). It was found that the fabricated films possessed a strong durability of a friction, exhibiting no peeling, cracking, and breaking in the films after TL measurements. These results will facilitate a development of novel TL skin sensors.

We successfully developed a novel elasticoluminescent (EML) material with water resistance, CaAl2Si2O8:Eu2+ (CAS). The crystal structure, photoluminescence (PL) and EML properties were characterized for both CAS and the typical EML material SrAl2O4:Eu2+(SAO). Contrary to SAO, CAS showed superior water resistance property. No changes were found in the XRD patterns, and the PL, EML intensities, during the whole examination of water immersion test.