Papers by Keyword: Mechanoluminescence

Abstract: Stress and stress concentration are one of the main factors of invalidating load-bearing structural members. Stress detection becomes an important part of industrial production. Mechanoluminescent (ML), which is produced by mechanical stimulation acting on materials, has been suggested to use in stress detection. This work focuses on the development and mechanism of ML, concludes with the applications of ML on the stress measurement, and discusses the specific challenges to the future directions of ML.

Abstract: Mechanoluminescence (ML) material is a novel functional material, showing a great potential on stress distribution of buildings, machine parts and other solid components. Novel ML materials NaAlSiO₄:Eu²⁺,Ln³⁺(Ln=Ho, Nd, Dy) were prepared by a solid-state sintered method, And their microstructure, ML and PL properties were investigated. ML spectra were similar to the PL spectra with an emission band at 550nm, originating from transition 5d-4f of Eu²⁺, and other three emission peaks at 611 nm, 590nm and 578 nm, respectively ascribed to the transitions of ⁵D₀ →⁷F₂, ⁵D₀ →⁷F₁ and ⁵D₀ →⁷F₀ of Eu³⁺ ions. Thermoluminescence (ThL) was measured to characterize traps in NaAlSiO₄:Eu²⁺,Ln³⁺(Ln=Ho, Nd, Dy). Diversity of ThL curves demonstrated co-doped Ln³⁺ change trap levels in NaAlSiO₄:Eu²⁺.

Abstract: The present paper reports both the experimental and mathematical aspects of elastico-mechanoluminescence (EML), plastico-mechanoluminescence (PML) and fracto-mechanoluminescence (FML) of coloured alkali halide crystals in detail, and thereby provides a deep understanding of the related phenomena. The additively coloured alkali halide crystals do not show ML during their elastic and plastic deformation. The ML emission during the elastic deformation takes place due to the mechanical interaction between bending dislocation segments and F-centres, and the ML emission during plastic deformation takes place due to the mechanical interaction between the moving dislocations and F-centres. The ML emission during fracture is also caused by the mechanical interaction between the moving dislocations and F-centres; however, in certain hard crystals like LiF, NaCl, NaF, etc., fracto ML also occurs due to the gas discharge caused by the creation of oppositely charged walls of cracks. The EML, PML, and solid state FML spectra of coloured alkali halide crystals are similar to their thermoluminescence spectra and afterglow spectra. However, the fracto ML spectra of certain hard crystals like LiF, NaCl, NaF, etc., also contain gas discharge spectra. The solid state ML spectra of coloured alkali halide crystals can be assigned to deformation-induced excitation of halide ions inV₂-centres or in other hole-centres. Whereas, the intensity of EML and FML increases linearly with the applied pressure and the impact velocity, the intensity of PML increases quardratically with the applied pressure and the impact velocity because of the plastic flow of the crystals. Both I_m and I_T increase with the density of F-centres in the crystals and strain rate of the crystals; however, they are optimum for a particular temperature of the crystals. The ML of diminished intensity also appears during the release of applied pressure. Expressions are derived for the elastico ML, plastico ML and fracto ML of coloured alkali halide crystals, in which a good agreement is found between the experimental and theoretical results. Many parameters of crystals such as band gap between the dislocation band and interacting F-centre energy level, radius of interaction between dislocations and F-centres, pinning time of dislocations, work hardening exponent, velocity of cracks, rise time of applied pressure, lifetime of electrons in the dislocation band, lifetime of electrons in shallow traps, diffusion time of holes, critical velocity of impact, etc., can be determined from the ML measurements. The ML of coloured alkali halide crystals has potential for self-indicating method of monitoring the microscopic and macroscopic processes; mechanoluminescence dosimetry; understanding dislocation bands in crystals; interaction between the dislocations and F-centres; dynamics of dislocations; deformation bleaching of coloration, etc. The ML of coloured alkali halide crystals has also the potential for photography, ML memory, and it gives information about slip planes, compression of crystals, fragmentation of crystals, etc.Contents of Paper

Abstract: Elastico-mechanoluminescence (EML) is a type of luminescence induced by elastic deformation of solids. The present paper reports the elastic-ML of thermoluminescent crystals such as X-or γ-irradiated alkali halide crystals, ZnS:Mn, and ultraviolet irradiated persistent luminescent crystals. Generally, all the elastico-mechanoluminescent crystals are thermoluminescent, but all the thermoluminescent crystals are not the mechanoluminescent. The elastico-mechanoluminescence spectra of crystals are similar to their thermoluminescence spectra. Both the elastico-mechanoluminescence and thermoluminescence arise due to the de-trapping of charge carriers. As elastico-ML of persistent luminescent crystals depends on both the density of filled traps and piezoelectric field, the intense thermoluminescent crystals may not be the intense mechanoluminescent crystals. When a sample of X-or γ-irradiated alkali halide crystal, UV-irradiated persistent luminescent microcrystals mixed in epoxy resin, or a film of ZnS:Mn nanoparticles is deformed in the elastic region by the pressure rising at fixed pressing rate for a particular time, or by a pressure of triangular form, or by a pressure pulse, then after a threshold pressure, initially the EML intensity increases with time, attains a maximum value and later on it decreases with time. In the first case, the fast decay time of EML is related to the time-constant for stopping the moving crosshead of the testing machine; in the second case, generally the fast decay does not appear; and in the third case, the fast decay time is equal to the rise time of the pressure pulse. However, in all the cases, the slow decay time is related to the lifetime of re-trapped charge carriers in the shallow traps lying in the region where the piezoelectric field is negligible. When the sample is deformed by the pressure rising at fixed pressing rate for a particular time, or pressure of triangular form, then the ML appears after a threshold pressure and the transient EML intensity increases linearly with the applied pressure; however, the total EML intensity increases quadratically with the applied pressure. The EML intensity of persistent luminescent crystals decreases with increasing number of pressings. However, when these crystals are exposed to UV light, then the recovery of EML intensity takes place. The mechanical interaction between the bending segment of dislocations and filled electron traps is able to explain the elastico-ML of X-or γ-irradiated alkali halide crystals. However, the piezoelectrically-induced de-trapping model is suitable for explaining the ML of persistent luminescent crystals and ZnS:Mn. The investigation of elastico-ML may be helpful in understanding the thermoluminescence and the investigation of thermoluminescence may be helpful in understanding elastico-ML. Furthermore, similar to the thermoluminescence, the mechanoluminescence may also find application in radiation dosimetry. Expressions are derived for the elastico-ML of thermoluminescent crystals, in which a good agreement is found between the experimental and theoretical results. Finally, the application of the elasticoML of thermoluminescent crystals in light sources, displays, imaging devices, sensing devices, radiation dosimetry and in non-destructive testing of materials are discussed.Contents of Paper

Abstract: This paper studied the mechanoluminescence of the CaAl₂Si₂O₈:Eu²⁺_x, Dy³⁺_y phosphors. The crystal structure, photoluminescence (PL) and mechanoluminescent intensity of the phosphors were investigated. The emission peak of CaAl₂Si₂O₈: Eu_x²⁺ had a redshift from 418 nm to 428 nm due to the increase of the crystal filed intensity around Eu²⁺ with the increase of Eu²⁺ ion content. The ML (mechanoluminescence) emission of CaAl₂Si₂O₈:Eu_0.01and CaAl₂Si₂O₈:Eu²⁺_0.01, Dy³⁺_0.02 can be seen by the naked eyeswhen compressive loads were appliedon the samples. Whats more, the addition of Dy³⁺can increase the ML intensity of CaAl₂Si₂O₈:Eu_0.01. The ML and PL spectra of the sample CaAl₂Si₂O₈:Eu²⁺_0.01, Dy³⁺_0.02 are identical, located at 428 nm.

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.