Papers by Author: Chao Nan Xu

Abstract: Calcium silicate phosphors, Ca2-xSiO4(CS):Eu3+x, CS:Eu2+x and Ca2-y-zMgSi2O7 (CMS):Eu2+y,Dy3+z were prepared by the solid state reaction. The phases in CS:Eu3+ system were β- and αL’ -types. The fluorescent color under a black-light irradiation was red and the emission spectrum consisted of 590nm(αL’), 615nm(β) and 625nm(αL’) peaks. The emission intensity took a maximum value at x=0.2. The addition of B3+ accelerated the solid solution of Eu3+. The phase in CS:Eu2+ system was β-type only. The fluorescent color was yellow-green(520nm). The emission intensity took a maximum value at x=0.01. The CMS product showed the akermanite phase. The lattice constants of CMS:Eu2+ increased with increasing Eu content, but those became constant at y>0.05. The fluorescent color of CMS:Eu2+ was yellow-green and the emission intensity took a maximum value at y=0.03. In the case of CMS:Eu2+0.03,Dy3+z, the fluorescent color and the afterglow color were same, yellow-green. The emission intensity took a maximum value at z=0.06. The longest afterglow time, 23min., was obtained at z=0.09. The trap depth were 0.64-0.69 eV.

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: This paper describes a study on the application of smart mechanoluminescence (ML) sensor to structures for the visualization of stress distribution. Smart thin film sensor of ML material SrAl2O4:Eu/polyme is coated on the surface of structure. The sensor will emit visual light when the structure is subjected to deformation. The light intensity is proportional to the strain energy density and the equivalent strain of the stressed material based on the energy viewpoint and experimental facts. The distribution of visual light intensity is recorded using CCD camera or ordinary camera. Then the stress distribution can be evaluated from the distribution of visual light intensity based on solid mechanics and the relationship between light intensity and equivalent strain. Compression test of a disk with coated SrAl2O4:Eu/epoxy film sensor is conducted to compare the visual light distribution with the stress distribution obtained from finite element analysis. Furthermore, tensile test of a rectangular specimen with a coated SrAl2O4:Eu/polymer film sensor is performed to demonstrate the relationship between visual light intensity and strain. Experimental and numerical results show that the smart sensor of ML material SrAl2O4:Eu/polymer is an effective strain sensor to directly visualize the stress distribution in real time.

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.