Deformation Luminescence Research Articles

Influence of compressive load and heat treatment on deformation luminescence of KCl:Eu2+ single crystals exposed to X-ray

When KCl:Eu2+ single crystals were exposed to X-ray and were plastically deformed by compression at 50 µm min−1, the peak appears around 330 K on the thermoluminescence (TL) glow curve under the influence of the compressive load below 200 N. The peak is termed 330 K peak here. Its intensity becomes slightly large with the compressive load and also depends on the quenching temperature above about 473 K for the preparation of sample. Furthermore, the 330 K peak disappears on the TL glow curve by the heat treatment: annealing at 953 K for 16 h, followed by gradually cooling to room temperature within 24 h. The variations in the 330 K peak height are related to the density of dislocations in the sample. On the absorption spectrum for the crystal, the peak height at the wavelength of 560 nm decreases by the heat treatment. This result is supposed to be caused by the phenomenon that dislocation density is reduced and some colour centres on the 330 K peak etc. are removed in the annealing process of the crystal.

Deformation luminescence of X-ray-irradiated KCl:Eu2+ single crystals by compression

A new peak appears around 330 K on the thermoluminescence (TL) glow curve under the influence of compressive deformation for X-ray-irradiated KCl:Eu2+ (0.02 mol%) crystal. This new peak is termed 330 K peak here. Deforming the crystal by the compression, mechanoluminescence intensity varies according to the three-stage strain hardening of stress-strain curve and depends on dislocation motion during plastic deformation of the crystal. The 330 K peak is also variable with strain in accordance with the variation of stress and correlates with dislocation motion in the crystal. Analysing the data on F- and thermal-bleaching effects of the compressed crystal, the colour centre on the 330 K peak has a new energy-band near F-band. The TL spectrum of the compressed and subsequent X-ray-irradiated KCl:Eu2+ crystal has a peak of 420 nm at the 330 K peak. From this experimental result, it is deduced that the 330 K peak relates to the excited Eu2+ ions as the origin of luminescence.

Creation and Investigation of Mechanoluminescent Coatings based on Polymethylmethacrylate and Phosphor Powder SrAl2O4: (Eu2+,Dy3+)

Deformation luminescence of a composite obtained on basis of the polymer material polymethylmethacrylate and fine-dispersed powder of SrAl2O4:(Eu2+, Dy3+) phosphor is investigated. The luminescent (sensory) layer responsive to mechanical action is formed in the surface layer of the polymethylmethacrylate that is transparent in the visible spectrum. The kinetics of deformation luminescence and the photoluminescence spectra of the SrAl2O4:(Eu2+, Dy3+) phosphor microparticles in the polymethylmethacrylate matrix have been studied. Photoluminescence was excited by the nanosecond pulses of the laser with the wavelength λ=355 nm. The shock action on the sensitive luminescent layer was realized by a hammering device and an impulse of an acoustic wave generated by a nanosecond laser pulse. It has been shown that the produced mechanoluminescent layer is highly sensitive to short acoustic and mechanical shock (normal and tangential) actions and can be used in registration and visualization of mechanical actions.

Mechanoluminescence of a composite based on polymethylmethacrylate and fine-disperse powder of SrAl2O4:(Eu2+, Dy3+) phosphor

The paper deals with photoluminescence and deformation luminescence (mechanoluminescence) of a composite material based on fine-disperse powder of phosphor SrAl2O4:(Eu2+, Dy3+) and polymethylmethacrylate that is transparent in the visible region. The luminescent (sensory) layer responsive to mechanical action was formed in the surface layer of the polymethylmethacrylate. To excite of photoluminescence the short pulses of a nanosecond laser were used. Mechanoluminescence was excited by the short acoustic impulses generated by a nanosecond laser. New information about the energy levels of impurities was obtained.

The deformation stimulated luminescence in KCl, KBr and KI crystals

Currently, strengthening of the intensity of luminescence in alkali halide crystals (AHC) at lattice symmetry lowering is discussed as a promising direction for the development of scintillation detectors [1-3]. In this regard, for the study of anion excitons and radiation defects in the AHC anion sublattice at deformation, the crystals with the same sizes of cations and different sizes of anions were chosen. In the X-ray spectra of KCl at 10 K, the luminescence at 3.88 eV; 3.05 eV and 2.3 eV is clearly visible. The luminescence at 3.05 eV corresponds to the tunneling recharge [F*, H]. Luminescence at 3.88 eV is quenched in the region of thermal destruction of F′-centers and characterizes tunneling recharge of F′, VK-centers. In KCl at 90 K, the luminescence of self-trapped excitons (STE) is completely absent. In KBr at deformation not only STE luminescence, but also deformation stimulated luminescence at 3.58 eV were recorded, the last one corresponds to tunneling recharge of F′, VK-centers. In KI crystal at 10 K and 90 K at deformation, only STE luminescence is enhanced. There are no deformation luminescence bands in KI compares with KBr and KCl crystals.

Low temperature photoluminescence and deformation luminescence of microparticles SrAl2O4:(Eu2+, Dy3+) in a matrix of photopolymer

The paper deals with low-temperature photoluminescence and deformation luminescence (mechanoluminescence) of a composite material based on fine disperse powder of phosphor SrAl 2 O 4:( Eu 2+, Dy 3+) and photopolymerizing resin that is transparent in the visible region. New information about the energy levels of impurities and defects was obtained. It has been found that at low temperatures (T = 15 ÷ 200 K) the photoluminescence spectrum of SrAl 2 O 4:( Eu 2+, Dy 3+) presents two partially overlapping wide bands with the maxima at λ1 max = 446 nm and λ2 max = 517 nm. The strong interaction of energy states of the bands results in temperature quenching of the short-wave band of luminescence (λ1 max = 446 nm) and its complete attenuation at T ≥ 200 K. The results were used to describe the mechanism of persistent luminescence and mechanoluminescence of SrAl 2 O 4:( Eu 2+, Dy 3+).

Investigation of the yield process by deformation luminescence of X-ray irradiated KCl:Ca2+

Abstract It is found that deformation luminescence gives us information about the microscopic yield process of X-ray irradiated KCl:Ca 2+ . The stress-strain curve has a macroscopic yield point. But we find that luminescence appears to start before the macroscopic yield. This means that dislocation begin to move before the macroscopic yield because deformation luminescence is attributed to radiation-induced dislocation motion. The beginning of luminescence is considered to be the microscopic yield. Investigating the dependence of microscopic yield stress on strain rate and impurity concentration gives us additional information. The activation volume obtained from the dependence of microscopic yield stress on strain rate is comparable to the value estimated from the concentration of impurity. Then the dislocation starts to move overcoming impurity-vacancy dipoles as obstacles to dislocation motion. The dislocation density starts to increase at the microscopic yield point and then sharply increases to the macroscopic yield.

Deformation luminescence of X-irradiated KCl:Eu2+ by bending test

It is well known that luminescence occurs during plastic deformation of X-irradiated alkali halide crystals. Luminescence pattern of KCl single crystals doped with europium has been observed during bending tests by using a CCD camera. Luminescence begins on both the fulcrum contact and opposite sides of a crystal at the beginning of plastic deformation. Several luminescence lines run along slip bands toward neutral axis from the outside of a sample in the direction of 45 degrees. Flash sometimes occurs both in the tension area and in the compression one. As deformation proceeds the luminescence lines are confused and right triangle-like luminescence pattern appears symmetrically on both sides of a central fulcrum in the compression area as well as in the tension one for three point bending tests. Strong flash has taken place in the triangle-like area just at fracture. But relatively homogeneous luminescence between two inner fulcrums has been observed for four point bending tests.

Effect of ultrasonic oscillatory stress on deformation luminescence of X-irradiated [formula omitted

Luminescence has been observed during deformation of X-irradiated alkali halide crystals. And also, it has been observed at fracture or under superimposition of ultrasonic oscillation. These phenomena are useful for studying the deformation of crystals. We have investigated luminescence during the deformation of X-irradiated KCl : Eu 2 + and under superimposition of oscillation. The luminescence intensity rapidly increases at the beginning of plastic deformation. The intensity roughly remains constant for a while and is then followed by gradual decreasing. The variation of luminescence intensity seems to correspond to the deformation stage of the crystal. The spectrum of deformation luminescence (DL) has a peak of 420 nm due to Eu 2 + . Superimposition of oscillation during plastic deformation of crystals causes a decrease in stress along with additional luminescence (sonoluminescence, SL). The SL intensity also appears to correspond to the deformation stage. SL/DL is found to be proportional to stress decrement due to superimposition of ultrasonic oscillation irrespectively of strain. DL has been found to occur mainly at the intersection of slip bands.

Deformation luminescence produced during application and release of pressure on to gamma-irradiated CaF2:RE crystals

Calcium fluoride CaF2 is an interesting host lattice for rare earth (RE) activators. CaF2 crystals doped with different concentrations of Dy, Ce, Er and Gd have been grown by the Bridgman technique and their deformation luminescence (DL) induced by room temperature gamma irradiation has been recorded. When a uniaxial pressure is applied on to gamma-irradiated CaF2:RE crystals, initially the DL intensity increases with time, attains a maximum value and then it decreases with time. Although the DL intensity produced during the release of pressure is less, its rise and decay behaviours are similar to that obtained during the application of pressure. The DL intensity depends on dopant, concentration of dopant, irradiation doses and mass of the load or applied pressure. It is suggested that the moving dislocation produced during deformation of crystals capture holes from hole trapped centres (like perturbed Vk centre) and the subsequent radiative recombination of the dislocation holes with electrons give rise to DL.

Strong elasticoluminescence from monoclinic-structure SrAl2O4

Elastico-deformation luminescence in strontium aluminates was investigated systematically using precisely controlled pure-phase Eu-doped strontium aluminates of SrAl12O19, Sr4Al14O25, SrAl4O7, α-SrAl2O4, β-SrAl2O4, Sr3Al2O6 and their mixed phases. This study revealed that only the α-SrAl2O4 phase produces strong elastico-deformation luminescence; other strontium aluminates show no deformation luminescence. Correlation of deformation luminescence and crystal structure was found. The α-SrAl2O4 has the lowest symmetry, crystallizing in a monoclinic structure. This finding can be applied in designing strong elastico-deformation-luminescent materials.

Intense visible light emission from stress-activated SrMgAl6O11:Eu

We have investigated deformation luminescence phenomena and the constituent phases of SrMgAl6O11:Eu. The deformation luminescence is clearly visible to the naked eye in air, and the luminescence intensity is the highest among the materials reported. Using x-ray diffraction the constituent phases of SrMgAl6O11:Eu are determined to be SrAl2O4, SrMgAl10O17, and MgAl2O4. The deformation luminescence center has been identified as the Eu2+ ion from the deformation and photoluminescence studies of the three-phase composite. The thermoluminescence glow curve of the composite indicates the trapping levels around room temperature. This result means that the three-phase structure of the composite influences the high deformation luminescence intensity.

Intense Deformation Luminescence from Sintered Sr3Al2O6:Eu.

We have investigated the deformation luminescence (DL) phenomena in sintered Sr3Al2O6: Eu. The DL from sintered Sr3Al2O6: Eu was clearly visible to the naked eye in the atmosphere, and was produced owing to the physical processes induced during deformation. The DL was sensitive to stress and was observed below the pressure of 10MPa. There is no report on the DL of sintered ceramic, the DL phenomenon of sintered ceramic is first reported first to our knowledge. The DL intensity of sintered Sr3Al2O6: Eu decreased on repetitive application of stress, but it was completely recovered by irradiation with ultraviolet light. The DL intensity was recovered by not only ultraviolet light but also visible light. It is suggested that Sr3Al2O6: Eu is a suitable DL material, which shows repeated DL with undiminished intensity. We think that the DL mechanism arises from the movement of dislocations or heat and recombination between electrons and holes released from these traps associated with doped Eu2+ centers.

Triboluminescence with and without Air

Twenty-three triboluminescent organic and inorganic materials were examined for crystal symmetry, differences between photoluminescence and triboluminescence emission spectra, spectroscopic evidence of an electrical discharge, and persistence of activity under liquids; some were also tested under other atmospheres. These experiments indicate that 18 materials were excited by a discharge, by either electron bombardment of the material or secondary excitation by the UV emissions of the surrounding gas. Five are apparently excited without a discharge, probably by the defect recombination characteristic of deformation luminescence.

Elementary acts of deformation luminescence

It is shown that the earlier proposed model of deformation luminescence in coloured alkali-halide crystals, based on the capture of an F-electron into a dislocation band followed by its transportation to the activator centers, is not only capable to explain the main rules of deformation luminescence but is also in quantitative agreement with the experiment.

Deformation Luminescence in gamma-irradiated KCl single crystals

Abstract Deformation Luminescence(DL) is studied on KCl crystal colored by γ-irradiation. The spectra analysis of DL and thermoluminescence reveals that F-center plays a role as electron donor through the interaction with moving dislocation and V2-center is a probable luminescence center. A theory is presented for understanding the deformation rate and temperature dependences of DL intensity.

Investigation of failure of composite materials by the method of deformation luminescence in a broad velocity range of loading

The article presents a way of investigating failure of materials with the aid of the method of deformation luminescence (DL) and describes the results of tests with specimens of laminated glass reinforced plastic with reinforcing structure (O2; ±60) and (±30; 902) in static and dynamic tension. Diagrams are plotted of the change of intensity of DL and stress σ11 vs. time at a speed of impact 0.5 and 1 m/sec, and also under static loading at the rate of 3 mm/min. It is shown that static and dynamic tension of laminated glass reinforced plastic is accompanied by DL expressing the jumpwise nature of step-by-step failure of the material.

Theory of deformation luminescence in KCl crystal

A theory of deformation luminescence (DL) in KCl crystal colored by γ-irradiation is presented for understanding the characteristics of the DL intensity I. The intensity calculated by simple rate equations describing the change in the numbers of luminescence centers and electrons explains well the deformation rate and temperature dependence of I.

Deformation luminescence in gamma-irradiated alkali halides

Abstract The deformation luminescence (DL) at a constant deformation rate in KCl crystal colored by γ-irradiation was studied, focusing on what the luminescence center is that is relevant to the DL phenomenon. It was found from the comparison of the spectra in DL and those in the thermoluminescence that the V2-center as luminescence center as well as the F-center as electron donor play a dominant role in the present process.

On the mechanisms of thermoluminescence and deformation luminescence in gamma-irradiated KCl

Abstract Thermoluminescence (TL) and deformation luminescence (DL) studies in KC1 γ-irradiated at room temperature are reported. The roles that F-centres and their higher conglomerates on the one hand, and V2- and V3-centres as recombination centres on the other hand, play in these processes are specified. Two peaks at 2.5 eV and 3 eV are observed in the emission spectra of both TL and DL. The close relationship between TL and DL is confirmed.