Papers by Author: Hiroshi Yamada

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: Dynamic visualization of stress distribution even due to a small deformation has been realized by coating the surface of the test object of metal with a upgrade mechanoluminescence (ML) material of SrAl2O4:Eu (SAO). In this paper we report the application of this ML sensing technique to stress concentration analysis on an aluminium plate. And the comparison with a theoretical calculation demonstrated that the ML intensity of SAO sensing film correlates linearly with von Mises stress on metal surface and the observed real-time ML images quantitatively reflect stress concentration.

Abstract: 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.

Abstract: In this paper, we demonstrate that a dynamic stress concentration around Lüders band can be directly displayed using mechanoluminescence (ML) sensing film of SrAl2O4:Eu (SAO) coated on the surface of metal. Uniaxial tensile test of an aluminum alloy (2.5% Mg) plate coated with the SAO sensing film was performed and the ML images were recorded using a high-speed camera. Captured ML images confirmed the formation and propagation of Lüders band clearly in real time.

Abstract: We have successfully developed a multifunctional ceramics, europium-doped feldspar MAl2Si2O8:Eu (MASE, M=Ca, Sr, Ba) and demonstrated that MASE was able to emit high mechanoluminescence (ML), strong photoluminescence (PL) and electroluminescence (EL). According to the XRD measurement result, the space group of MASE was identified to P1 .The ML intensity increased proportionally with the increase of the compressive load, which suggests an efficient conversion of mechanical to optical energy. Furthermore, strong PL and EL emission from MASE were confirmed. The PL, ML, and EL spectra were found to be similar in both peak shape and position, which indicates all the emissions result from 5d-4f transition of Eu2+.

Abstract: 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.