Thermoluminescence Spectra Research Articles

Long persistent luminescence and photostimulated luminescence in Y3GaO6:Pr3+ phosphor

Long persistent luminescence (LPL) phosphors have a wide range of potential applications, including multi-color anticounterfeiting and long-term continuous detection of short-wavelength ultra-violet (UV) radiation. However, developing a stable carrier container that can provide ultra-long carrier storage for activators and visible multi-color LPL is a challenging task. In this work, we presented a series of Pr3+-doped Y3GaO6 (YGO) LPL phosphors that take full advantage of the synergistic relationship between the host lattice, emitters, and carrier traps. The host provides a suitable lattice site for rare-earth Pr3+ and offers a broad band gap of 5.69 eV to hold traps with depths ranging from 1.01 to 2.17 eV. We observed LPL that was visible to the naked eye for 6 h after excitation, and strong thermoluminescence (TL) spectra could be detected after the phosphor was placed in darkness for 20 days at room temperature. Additionally, we observed photostimulated luminescence under 980 nm and 808 nm laser irradiation with a power density of 5 W cm-2, indicating that low-energy excitation not only leads to LPL but also accelerates the elimination of previously stored carriers. After investigating the crystal structure and possible defects generated in the materials, we proposed a mechanism for LPL. Our findings demonstrate the potential of Pr3+-doped YGO LPL phosphors for a range of applications, such as multi-color anticounterfeiting and long-term continuous detection of short-wavelength UV radiation.

Cation defects succeed in triggering super stability of narrow-band blue-emitting phosphors Ca3Sc2Si3O12: Bi3+ for backlighting display application

High-performance white light-emitting diodes (WLEDs) used for backlighting display applications require innovative and thermally stable narrow-band emission phosphors, particularly non-rare-earth Bi3+-activated phosphors. In this study, we demonstrate a defect-engineering strategy to create novel anti-thermal quenching phosphors Ca3Sc2Si3O12: xBi3+ (CSSO: xBi3+). Through structure refinement of CSSO: 0.06Bi3+ phosphor, we found that Bi occupies both Ca and Sc sites in the CSSO lattice. Direct visualization of atomic-resolution TEM and thermoluminescence spectra confirmed the formation of point defects due to the non-equivalent substitution of Ca2+ for Bi3+. Fluorescent-decay analysis revealed that two luminescence sites contribute to the blue-emitting of CSSO:Bi3+ phosphors. CSSO: 0.06Bi3+ phosphor exhibits outstanding thermal stability, with an integrated emission intensity of 103.6% at 423 K compared to that at 298 K. However, the addition of Li or Na as charge compensators reduced cationic defects, leading to a decrease in thermal stability. We believe that VCa″ defects are primarily responsible for the anti-thermal quenching behavior of CSSO: xBi3+ phosphors. An optimized CSSO: 0.06Bi3+ phosphor-based WLED displays a high color rendering index (CRI) of 90 and a wide color gamut (90% National Television System Committee (NTSC) standard), indicating its potential for use in industrial applications as a backlighting display.

Multimode Dynamic Photoluminescence of Bi3+-Activated ZnGa2O4 for Optical Information Encryption.

Optical storage technology for information encryption is a popular means of safeguarding information. Herein, a Bi3+-activated ZnGa2O4 multimode dynamic photoluminescence (PL) material is developed. Upon being irradiated with an ultraviolet lamp at a fixed excitation wavelength of 254 nm, the ZnGa2O4: x% Bi3+ (x = 0.5-5.0) samples exhibit varying degrees of dynamic PL emission due to a distinct Bi3+ doping effect. The mechanism underlying the dynamic PL of ZnGa2O4: Bi3+ associated with Bi3+-activated trap concentration modulation is investigated using thermoluminescence spectra. Additionally, the ZnGa2O4: 5% Bi3+ sample shows a reversible thermally responsive dynamic PL with a color variation from blue to red upon heating from 283 to 393 K. Predesigned procedures based on single-wavelength-mediated photochromic and thermochromic dynamic PL emissions of ZnGa2O4: Bi3+ are designed for rewritable optical data storage and high-level information encryption. Also, an enhanced encryption scheme with a mask encoding technique applying a ZnGa2O4: Bi3+ hybridized polyvinylidene difluoride film is then proposed to increase the security level. Accordingly, this work provides a feasible way to rationally design dynamic PL material offering more creative designs for safeguarding information via encryption.

The role of capping agents on the trapping levels structure and luminescent emission of SrMoO4 phosphors

In the present work, we investigate the thermoluminescence (TL) and optically stimulated luminescence (OSL) from strontium molybdate SrMoO4 powders designed with different capping agents. The samples were prepared through co-precipitation and processed in a Microwave-Assisted Hydrothermal (MAH) system. The structural, optical, and morphological characteristics were investigated using Raman, Fourier transform infrared spectroscopy (FTIR), DRX, ultraviolet-visible (UV–vis) absorption, and Scanning electron microscopy (SEM). The TL glow curves recorded from as-prepared and irradiated samples with beta particles reveal that their intensity and profile depend on the used capping agent. The trapping depth energy, determined from the TL glows curves, ranges from 1.02 to 2.23 eV for the as-prepared samples and from 0.9 to 2.33 eV for the irradiated phosphors. The residual TL spectra, registered from successive readouts, reveal that the thermal treatment shifts the glow curve to lower temperatures suggesting the formation of shallower trap states. The results reveal that the OSL signal and its behaviors with the radiation dose depending on the employed capping agent. The results show the TL and OSL signal's dependence on the structural properties and support the potential application of SrMoO4 powders as an OSL detector.

Structural, photoluminescence, and thermoluminescence behaviors of Samarium doped CaWO4 phosphor

This manuscript reports the crystal structure, photoluminescence and thermoluminescence behavior of Samarium doped CaWO4 i.e., Ca1-xSm2x/3WO4 (x: 0.01, 0.02, 0.03, 0.04, 0.05) synthesized by conventional solid state reaction method. The X-ray diffraction data are analyzed using Rietveld refinement method and showed that samples exhibit cento-symmetric tetragonal crystal structure with I41/a (No. 88) space group. The unit cell volumes are increased with rising Sm composition. The energy bandgaps of the phosphors are observed by the UV–Visible absorbance spectroscopy and found to be directly proportional to the cell volume. Photoluminescence properties are considered from the excitation as well as emission spectra. These spectra resulted that the critical quenching concentration occurred at x = 0.02 due to the dipole–dipole interactions with critical energy transfer distance of 20 Å. The color purity and correlated color temperature values of the sample can be measured from the CIE Chromaticity. It is also described the orange-red emission color of the phosphors. Lower UV dosimetry with second order kinetics is obtained from the thermoluminescence spectra of x = 0.02 with 30 min UV radiation.

Thermoluminescence investigations and kinetic analysis of highly sensitive LiCaAlF6: Eu,Y phosphor for dosimetric applications

The paper presents detailed thermoluminescence characterization and kinetic analysis of highly sensitive and dosimetric grade lithium calcium aluminum fluoride doped with europium and co-doped with yttrium (LiCaAlF6:Eu,Y). It is synthesized by melt processing technique. The thermoluminescence (TL) and optically stimulated luminescence (OSL) correlation was systematically studied. The study reveals that the OSL signal is attributed to the observed TL peaks in this material. Thus, same defects are responsible for TL and OSL in LiCaAlF6:Eu,Y. Further characterization involved measurement of TL emission spectrum, OSL emission spectrum, steady state photoluminescence (PL) spectra, phosphorescence, sensitivity, fading, dose response etc. The TL sensitivity of this phosphor was observed to be ∼5 times and ∼3 times to that of CaSO4:Dy and commercially available Al2O3:C respectively. PL, TL and OSL emission spectra suggest that Eu2+ ion acts as a luminescence center in this material. Minimum measureable dose for the phosphor in TL mode was found to be 0.3 μGy with negligible fading post 10 days of irradiation. The fading of TL signal in this material is similar to the one observed for OSL signal. The thermal stability and hygroscopic nature of LiCaAlF6:Eu, Y were studied using thermogravimetric and differential scanning calorimetry techniques. Owing to the attributes like high sensitivity, wide dynamic dose range it stands as a viable and excellent phosphor material for various radiological and dosimetric applications.

Tailored luminescence of Bi doped Ca3Ga4O9 phosphors with the substitution of strontium ions

Bi3+ ion-doped phosphors have a wide range of applications in white light emitting diodes (W-LEDs), temperature sensing, long persistent materials and anti-counterfeiting. In this work, a series of Ca2.97-xSrxGa4O9: 3mol%Bi3+ phosphors were prepared via a high-temperature solid-state reaction process. X-ray diffraction (XRD), photoluminescence and 3D thermoluminescence spectra were collected to characterize the samples. The emission spectra of samples demonstrated that Bi3+ ions occupied two different Ca sites with different coordination. Due to the variations in crystal field splitting and site-selective occupancy of Bi3+, photoluminescence spectra can be adjusted sequentially when strontium ions were introduced. Additionally, a detailed analysis of the variation on the trap intensity and the energy transfer between the traps and the luminescence centers has been carried out by 3D-thermoluminescence with cation substitution.

A new insight into the mechanism of persistent luminescence phosphors SrS: Eu2+, Pr3+

The red persistent luminescence phosphors SrS: , (x = 0∼0.001, y = 0∼0.003) were synthesized by the solid-state reaction method in a weak reducing atmosphere of active carbon. The synthetic parameters, photoluminescence characteristics, and dynamic properties of thermoluminescence of the phosphors were studied systematically. According to the results of photoluminescence spectra of SrS: , , the energy level scheme of the phosphors was confirmed quantitatively. Based on the studies of the scanning electron microscope (SEM), UV-Visible absorbance spectra, afterglow decay curves, thermoluminescence(TL) spectra, and X-ray photoelectron spectroscopy (XPS) spectra, we found that the SrS: , (SSEP) phosphor presented the best persistent luminescence property, which mainly resulted from its outstanding absorbance characteristic, deeper depth of () defects, and fewer defect concentration belonging to the higher-order kinetics. Those comprehensive results deduced that a complex defect ()- should present in the Eu2+ doping phosphors, and the Pr3+ doping will produce defects, which can suppress the formation of () defects and increase their energy depth.

Investigation of photoluminescence, thermoluminescence, and energy transfer mechanism in Ce/Dy co-doped Sr2Al2SiO7

In the present manuscript, we report the luminescence properties and energy transfer mechanism of Ce/Dy co-doped Sr2Al2SiO7 (SASO) phosphors prepared through the solid-state reaction method. Phase identification was done through a powder X-Ray diffraction tool and the obtained diffractogram confirms the formation of the desired phase. The Photoluminescence excitation and emission spectra of the prepared samples were investigated. Photoluminescence studies revealed that the luminescence intensity rises with increasing Dy concentration and optimized intensity was observed at 1 mol%. The energy transfer in the host has been attained successfully to produce color tunability. The Commission International de I'Eclairage (CIE) chromaticity coordinates and correlated color temperature (CCT) has been calculated. The energy transfer mechanism is further investigated via Thermoluminescence (TL) spectra. Further, the TL properties of synthesized phosphors were analyzed via the glow curve method along with varying UV doses. As compared to the single-doped phosphors, the TL glow curve indicates that very high intensity is observed at very low UV doses and the major TL peak is located in a higher temperature region. The calculated kinetic parameter indicates that Ce/Dy co-doped SASO has both shallow and deeper traps. All these findings suggest the potential applicability of synthesized phosphors as a low UV dosimeter.

Intrinsic imperfect and zero thermal quenching property for a novel β-NaYF4:Eu3+,Tb3+ red-light emitting phosphor for NUV LEDs

Despite long-term development of LEDs, problems urgent to resolve is still existing. The most outstanding problem to tackle is luminescent stability at high temperature working situation. In this study, a novel type of β-NaYF4 based phosphor incorporated with Eu3+ and Tb3+ is reported. A series of β-NaYF4:0.065Eu3+,xTb3+ (x = 0.001, 0.002, 0.003, 0.004, 0.005) phosphors were synthesized by hydrothermal method. The sample β-NaYF4:0.065Eu3+,0.002Tb3+ possesses optimal luminescent property at room temperature. The mechanism of energy transfer from Tb3+ to Eu3+ ion is quadrupole-quadrupole interactions. The sample β-NaYF4:0.065Eu3+,0.002Tb3+ demonstrates zero thermal quenching (ZTQ) property at 303 K to 383 K. According to XRD and XPS characterizations, nonequivalent replacement between intrinsic ion Na+ and Y3+ were discovered, which finally leads to production of crystal defects. According to electron paramagnetic resonance (EPR) characterization and density functional theory (DFT) calculation, the type of crystal defect of β-NaYF4:0.065Eu3+,0.002Tb3+ is confirmed to be VY vacancies which are the predominant defect of crystal. The depths and densities of defects were calculated according to data of thermoluminescence spectra (TL spectra). Crystal defects play the role of electrons traps that could store electrons. Electrons stored in traps will be excited to excitation state of Eu3+ under the thermal stimulation to offset undesirable impact of thermal quenching (TQ), which leads to ZTQ property of the sample β-NaYF4:0.065Eu3+,0.002Tb3+. The CRI and CCT of fabricated WLED are 3830 K and 84.1, respectively.

Manipulation of the ratio of Li+/Zn2+ on the structure and persistent luminescence property of Li2Zn0.9992Ge3O8:0.08%Cr3+

AbstractLong persistent luminescence (LPL) materials have been widely applied and investigated in the fields of night‐safe, bio‐fluorescent labeling, and optical anti‐counterfeiting because of their unique properties of delayed luminescence. In this work, the focus of this research is to significantly improve the LPL properties of Li2Zn0.9992Ge3O8:0.08%Cr3+ by adjusting the ratio of Li+/Zn2+. On the one hand, when Li+:Zn2+ < 2:1 (Li1.97Zn1.0292Ge3O8:0.08%Cr3+), a deep‐red LPL is produced in the 650–900 nm band for more than 50 h, which is 2.5 times longer than that without regulation. From another perspective, when Li+:Zn2+ > 2:1 (Li2.01Zn0.9892Ge3O8:0.08%Cr3+), the intensity of LPL is enhanced about four times compared to unregulated. The relationship between traps and LPL was comprehensively investigated by analyzing thermoluminescence spectra. Biological tissue penetration experiments were performed and a set of anti‐counterfeit labels was designed. This research will provide guidance for the design of a novel persistent phosphor for the desired trap depth.

Near-Infrared Emission Material with Superlong Afterglow Performance and Its Multifunctional Applications.

A new near-infrared (NIR) emission material, BaSi1.5Ge2.5O9:Cr3+, with outstanding long afterglow properties is designed and synthesized successfully. Its structure, photoluminescence, and long afterglow emission features are studied in detail. Cr3+ occupies six-coordinated Ba2+ and Ge4+ sites in this system, which can emit characteristic broadband NIR light in the range of 700-1200 nm, and it has a long afterglow emission of more than 10 h. We calculated the band gap of the host at about 4.1 eV, the energy level distribution after Cr3+ doping, and the distribution of oxygen vacancies through density functional theory simulation, which theoretically proved the characteristic transition of Cr3+ and that the oxygen vacancies are crucial to form the defect energy levels. This is corroborated with the reflectance spectra, three-dimensional thermoluminescence spectra, and electron spin resonance (ESR) spectra. The oxygen-deficient environment favors the formation of oxygen vacancy defects and prevents the oxidation of Cr3+ to Cr6+, which are the key points for the luminescence and afterglow properties. A mechanistic model of defect formation and electron trapping and transport processes is successfully established. Finally, its multifunctional applications in information anticounterfeiting encryption, biological tissue penetration, and internal nondestructive testing and imaging are demonstrated.

Multicolor and multimode luminescence regulation and anti-counterfeiting application of lanthanide ions doped Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> phosphors

Multicolor and multimode luminescence materials have important applications in the field of information security encryption. However, the design and synthesis of multicolor multimode luminescent materials is still a challenge, and only several materials have been reported. In this paper, a series of single doped and double doped Li<sub>1–<i>x</i></sub>K<sub><i>x</i></sub>NbO<sub>3</sub>:Pr<sup>3+</sup>/Er<sup>3+</sup>/Tm<sup>3+</sup> phosphors are prepared by high temperature solid state method. The structure, morphology, optical properties and thermoluminescence (TL) spectra are characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), luminescence spectrometer and self-made heating device. Firstly, the effects of different values of K<sup>+</sup> content on the luminescence and trap distribution of LiNbO<sub>3</sub> materials are studied. The results show that the ionic lattice is distorted when a small quantity of K<sup>+</sup> ions replace Li<sup>+</sup>. With the addition of K<sup>+</sup>, the photoluminescence excitation (PLE) spectra monitored emission of 620 nm shows that the ratios of the absorption peaks from matrix (200–310 nm) to absorption peaks from the intrinsic transition of Pr<sup>3+</sup> ions 4f→5d (310–430 nm) change significantly, showing a double-peak characteristic. When the concentration of K<sup>+</sup> ions is 0.5, the absorption peak from the matrix disappears, which may be due to the phase transition of the matrix lattice caused by excessive K<sup>+</sup> ions or the introduction of a large number of defect energy levels into the matrix lattice. Moreover, K<sup>+</sup> ion doping can regulate the density and distribution of traps. TL curves show that a small quantity of K<sup>+</sup> doping increases the trap density of shallow traps. When a large quantity of K<sup>+</sup> is doped, the phase changes of matrix lattice and the defect density decrease. Secondly, the doping of Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> matrix by different luminescent centers (Pr<sup>3+</sup>/Er<sup>3+</sup>/Tm<sup>3+</sup>) is studied. The results show that the multicolor luminescence emission in red, blue and green bands and the tunable multimode luminescence (up/down conversion luminescence, afterglow luminescence and photo-stimulated luminescence) are realized by the selective excitation. According to the multicolor and multimode characteristics of the phosphors, a butterfly-shaped anti-counterfeiting pattern is designed. Owing to the different energy level positions of the luminescence centers, dynamic multicolor photoluminescence is realized by selective excitation at different wavelengths. Based on the upconversion luminescence characteristics of Er<sup>3+</sup> and the excellent afterglow characteristics of Pr<sup>3+</sup> in Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> material, the designed anti-counterfeiting pattern shows the dynamic color change and multicolor, multimode high-order anti-counterfeiting application.

Insights into blue-light activated red-emitting persistent luminescence from Pr3+-doped phosphors.

In recent years, a series of persistent luminescence materials excitable by blue light have been developed and widely used in many fields such as optical information storage, AC-LEDs, anti-counterfeiting and bio-imaging. However, it is still a long-standing challenge to develop a superior red-emitting persistent phosphor that can be efficiently excited by blue light. In this work, a novel blue-light excited red-emitting persistent phosphor CaCd2Ga2Ge3O12:Pr3+ was successfully synthesized by using a solid-state method, showing excellent luminescence properties. Moreover, the phase purity, crystal structure, photoluminescence spectra, afterglow emission spectra, and three-dimensional thermoluminescence spectrum were successfully investigated. Under 294 nm excitation, photoluminescence spectra show a single orange emission and a series of peaks centered at 492, 537, 568, 614 and 664 nm, which correspond to the 3P0 → 3H4, 3P0 → 3H5, 3P2 → 3H6, 1D2 → 3H4, and 3P0 → 3F2 transitions of Pr3+, respectively. Interestingly, after blue light excitation, the afterglow luminescence exhibits red long emission, which is attributed to the 1D2 → 3H4 transition of Pr3+. Through thermoluminescence spectra and three-dimensional thermoluminescence spectra, we analyze the reasons for the different colors of photoluminescence and afterglow luminescence. The results imply that there are two types of traps, and the depth of shallow traps and deep traps is calculated to be 0.684 and 0.776 eV, respectively. It is worth noting that the photoluminescence is attributed to the 4f2 → 4f5d and f → f transitions of Pr3+, and the afterglow luminescence is ascribed to a tunneling-related process and the transition of electrons from the valence band to the conduction band. The obtained red-emitting persistent phosphors provide a promising pathway toward AC-LEDs, multi-cycle bio-imaging and other fields.

Behaviour of Radio- Thermoluminescence (X-Ray Irradiated), Thermal and Structural Characterization of Limestone

In this study, it was reported radioluminescence properties of limestone from Kütahya, Turkey for the first time in this study, which has been the subject of many studies in both mineralogical and gemological fields. Limestone is the general name of carbonate roks, which is the mineral with typical colors according to the impurity elements in rock and exhibited luminescence properties under x-ray irradiation. The radio&thermoluminescence data were analyzed for limestone. Besides, x-ray diffraction pattern was created for structural characterization, scanning electron microscope images and energy dispersive x-ray spectroscopy maps were taken to determine morphological features. When the radioluminescence spectrum of the limestone was detailed, a broad emission consisting of several peaks was observed in the visible region. In the thermoluminescence spectrum taken after the x-ray excitation of the limestone, three thermoluminescence peaks were observed at 97 oC, 170oC and 320 oC. Also; TL kinetic parameters are reported; The activation energy (E) and frequency factor (s) of the first peak were determined in detail using the methods of peak shape and varying heating rates.

Thermostimulated luminescence and photoluminescence of microcrystalline zinc sulphide ZnS:Cu

In the work, photoluminescence (PL) and thermoluminescence (TL) spectra of a zinc sulfide phosphor series, namely microcrystalline ZnS:Cu obtained by self-propagating high-temperature synthesis (SHS), were obtained and analyzed. Based on the spectral analysis, the character of the influence of annealing parameters on the intensity of the “blue” (B) and “green” (G) PL bands is established. The behaviors of the PL and TL bands are compared and the TL bands in the blue and green spectral regions are identified. The TL mechanism was assumed to be the specific nature of the centers that cause the B- and G-bands of PL.

Bright persistent luminescence from Cu+ activated Al2O3–CaO photochromic glasses

Using the photochromic glass to prepare glass with long persistence lifetime is a new strategy to develop persistent luminescent (PersL) glass. A novel Cu + doped Al2O3–CaO PersL glasses were found according to the strategy. The Cu + doped Al2O3–CaO glasses were papered in reducing conditions, which not only showed double luminescence characteristic of Cu+ at 457 nm and 480 nm after irradiated by ultraviolet light source or sunlight, but also emitted bright and lasting green light after cutting off the excitation source. The persistence lifetime of the glass is positively correlated with the content of Al2O3, and the longest lifetime can reach 10.5 h. The spectral properties of the glasses were analyzed by absorption spectrum, fluorescence spectrum, thermoluminescence spectrum and EPR. Based on these results and the photochromic properties of the glass, the PersL is explained by a model of "storage" and "release" electrons generated by electronic defects in the glasses prepared in reducing atmosphere.

Neutron detection properties of thermoluminescent Sr2B2O5:Eu ceramics

Thermoluminescent (TL) ceramic materials have been developed for neutron detection on the basis of Eu-doped Sr2B2O5. A photoluminescence emission band at around 360 nm was observed for Sr2B2O5 doped with Eu at 0.1–0.3 mol% with respect to Sr, and is attributed to 5d–4f transition of Eu2+. The emission band was also observed in the TL spectra. TL glow peaks were observed at 340, 400, and 500 K in the TL glow curves after X-ray irradiation, and Sr2B2O5 doped with Eu at 0.2 mol% exhibited the highest TL intensity. After neutron irradiation, a significant difference in the TL intensities was observed between the ceramics containing enriched 10B and 11B owing to the contribution of 10B(n,α)7Li reaction to the observed TL. The difference in the TL intensities linearly increased with neutron fluence of, at least, 107–1011 neutrons cm−2. Hence, we succeeded in the development of TL materials for neutron detection.

A novel modification strategy for photochromic KSr2Nb5O15-based ceramics by establishing a heterojunction band structure

Because of their rapid response, high sensitivity, and excellent thermal and chemical stabilities, photochromic ceramics have attracted great potential for optical applications in anti-counterfeiting and optical information storage. However, the inferior photochromic contrast restricted the further development of photochromic ceramics. Herein, a novel modification strategy for photochromic behavior is proposed in a KSr2Nb5O15-based system. A new heterojunction band structure was established at the interfaces in ceramics by compositing with transition metal oxides and generated novel transition paths for the excited carriers. After compositing with the Nb2O5 second phase, the photochromic contrast △Rdec was almost doubled by additional color centers from the heterojunction structure. The related mechanism was confirmed by the photochromic behavior, thermoluminescence spectra and band structure features. Moreover, rapid, convenient and reversible laser bleaching behaviors was explored, and a more flexible anti-counterfeiting method was attempted through secondary laser adjustment of the photochromic pattern. This work aims to present a new modification viewpoint into photochromic ceramics by building a heterojunction structure.

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.