Al2O3 Crystals Research Articles

Overcoming the intrinsic brittleness of high-strength Al2O3–GdAlO3 ceramics through refined eutectic microstructure

High-strength ceramic materials are known for their exceptional mechanical properties; however, they are often plagued by brittleness, limiting their applications. Because of the inherent difficulty of dislocation glide and multiplication in ceramics, efforts to overcome the brittleness of ceramics by activating plastic deformation have faced challenges. This work demonstrates that Al2O3–GdAlO3 (Gadolinium Aluminum Perovskite: GAP) eutectic micropillars with submicron-scale fibrous microstructures exhibit remarkable plastic deformability. They displayed engineering plastic strains of up to 5% even at 25 °C, while the micropillars of Al2O3 or GAP single crystals exhibited brittle fracture similar to conventional high-strength ceramics. The plasticity in Al2O3–GAP eutectic was attributed to the activation of primary prismatic slip and secondary basal slip in the Al2O3 phase, which is typically considered inactive at room temperature. These findings suggest that plastic deformability can be achieved in high-strength ceramic materials by fabricating refined eutectic microstructures.

Observation of terahertz nonlinear absorption activity in Al2O3

We investigate the terahertz (THz) nonlinear absorption characteristics in a thin Al2O3 crystal using nonlinear THz spectroscopy. A THz saturable absorption performance with a high modulation depth (27.5%) and a relatively low saturable intensity (6.99 µJ/cm2) of Al2O3 is revealed, covering the THz spectrum from 0.1 to 8 THz. The inevitable presence of oxygen vacancies and impurities in Al2O3 single crystal results in the existence of free electrons within the conduction band. The transmission enhancement can be described by the change of the mobility of electrons due to intervalley scattering induced by THz pulses, based on first-principles calculations. Therefore, Al2O3 crystals have promising application potential in mode-locked devices for directly delivering broadband ultrashort THz pulses.

Unveiling the effects of support crystal phase on Cu/Al2O3 catalysts for furfural selective hydrogenation to furfuryl alcohol

Support crystal phase plays a crucial role in the controlled CO hydrogenation over the supported catalysts. Herein, the effects of Al2O3 crystal phase (α, θ, η, and γ) on the supported Cu-based catalyst is highlighted for furfural (FAL) hydrogenation to furfuryl alcohol (FA). The evaluation results show that Cu/η-Al2O3 exhibits the best performance (FAL conversion: 99.7 %, FA selectivity: 94.0 %), highest TOF value (29.3 h−1) and lowest apparent activation energy (66.3 kJ/mol). The comprehensive characterizations unravel that Cu/η-Al2O3 has the smallest Cu nanoparticles and the highest content of Cu+ and Cu0, which facilitates H2 dissociation and FAL adsorption. The reaction mechanisms suggest that Cu/η-Al2O3 has the strongest FAL adsorption and FA desorption capacity. Moreover, it is demonstrated that FAL is linear chemical adsorption on the catalyst surface in the η1(O) configuration, which avoids the furan ring hydrogenation, and thereby, results in the high FA selectivity. This work would provide some references for developing the high-efficiency CO hydrogenation catalysts.

High-temperature protection performance of Mg-doped Al2O3 protective layers on the thin film thermocouples

Mg-doped Al2O3 protective layers were deposited on Pt–PtRh10 (S-type) thin film thermocouples (TFTCs) by reactive magnetron sputtering. The changes in the composition, microstructure, and element distribution of the Mg-doped Al2O3 films before and after annealing at 1200 °C for 3 h were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The results indicate that incorporating MgO into Al2O3 as an enhancement phase not only inhibits the crystallization and phase transformation of Al2O3 but also promotes the formation of MgAl2O4, sequentially further enhancing the material's high-temperature protective properties. The thermoelectric properties of S-type TFTCs with 1.6 μm thick Al2O3 and Mg-doped Al2O3 protective layers were explored, respectively. The results of static calibration at high temperatures demonstrate that the TFTCs with the Mg-doped Al2O3 protective layer can operate at 1148 °C for over 96 h and at 1480 °C for a brief period. Following 4 calibration cycles, compared to the TFTCs with the Al2O3 protective layer, the average Seebeck coefficients of the TFTCs with the Mg-doped Al2O3 protective layer exhibit a slower decline rate, and its drift rate during the 4th cycle is merely 3.28 °C/h. The TFTCs featuring Mg-doped Al2O3 protective layers demonstrate extended lifetimes, superior high-temperature stability, and enhanced reliability when contrasted with those utilizing undoped Al2O3 protective layers. These attributes offer valuable insights into the progression of TFTC technology.

Hardness Distribution and Growth Behavior of Micro-Arc Oxide Ceramic Film with Positive and Negative Pulse Coordination.

Micro-arc oxidation (MAO) is a promising technology for enhancing the wear resistance of engine cylinders by growing a high hardness alumina ceramic film on the surface of light aluminum engine cylinders. However, the positive and negative pulse coordination, voltage characteristic signal, hardness distribution characteristics of the ceramic film, and their internal mechanism during the growth process are still unclear. This paper investigates the synergistic effect mechanism of cathodic and anodic current on the growth behaviour of alumina, dynamic voltage signal, and hardness distribution of micro-arc oxidation film. Ceramic film samples were fabricated under various conditions, including current densities of 10, 12, 14, and 16 A/dm2, and current density ratios of cathode and anode of 1.1, 1.2, and 1.3, respectively. Based on the observed characteristics of the process voltage curve and the spark signal changes, the growth of the ceramic film can be divided into five stages. The influence of positive and negative current density parameters on the segmented growth process of the ceramic film is mainly reflected in the transition time, voltage variation rate, and the voltage value of different growth stages. Enhancing the cathode pulse effect or increasing the current density level can effectively shorten the transition time and accelerate the voltage drop rate. The microhardness of the ceramic film cross-section presents a discontinuous soft-hard-soft regional distribution. Multiple thermal cycles lead to a gradient differentiation of the Al2O3 crystal phase transition ratio along the thickness direction of the layer. The layer grown on the outer surface of the initial substrate exhibits the highest hardness, with a small gradient change in hardness, forming a high hardness zone approximately 20-30 μm wide. This high hardness zone extends to both sides, with hardness decreasing rapidly.

Green syhthesis of aluminium oxide nanoparticles using Chrysophyllum albidum, Terminalia catappa and Mimusops Coriacea leaf extracts for antibacterial and antifungal activities

The study reports an environmentally friendly and simple green technique for the synthesis of aluminium oxide nanoparticles (Al2O3 NPs). The leaf extracts of Chrysophyllum albidum (chry.A), Terminalia catappa (Alm) and Mimusops Coriacea (Lam) were used as reducing and stabilizing agents. Microscopic characterisations of the nanoparticles were carried out such as TEM, SEM, X-RAY, FTIR, UV and antimicrobial application were conducted. The result of the analysis showed that transmission electron microscopy (TEM) of Al2O3 NPs revealed quasi-spherical particle shapes and showed the particle size distribution. X-ray diffraction (XRD) analysis revealed that the Al2O3 crystals are face-centered cubic (FCC) for Chry.A Al2O3 NP, Alm Al2O3 NP and Lam Al2O3 NP and the average crystallite size were given to be 54.4 nm, 58.3 nm and 25.8 nm while Fourier transform infrared (FTIR) results of Al2O3 NPs showed the existence of metal-oxygen Al-O and occurrence of carbonyl and hydroxyl groups from plant flavonoids. The electronic interaction of Al2O3 NPs was investigated with Ultraviolet visible spectroscopy (UV) and the results revealed 238 nm of the absorption capacity of Al2O3 NPs which is attributed to quasi-spherical structural arrangement and energy dispersive X-ray spectroscopy (EDS) verified the existence of elemental aluminium which revealed maximum peaks of Al-O. The synthesized metal oxide nanoparticles (Al2O3 NPs) were evaluated for antibacterial and antifungal actvitties and the results show that they were potent against gram-positive Staphylococcus aureus; and Candida albicans and Trichophyton rubrum. The chry. A Al2O3 NP was found to displayed higher activities of antibacterial against Staphylococcus aureus (gram-positive) than Alm Al2O3 NP and Lam Al2O3 NP. The antibacterial activities of Chry.A Al2O3 NP and Alm Al2O3 NP also showed maximum zone of inhibition with minimum inhibitory concentration MIC of 0.125 and 0.250 mg/mL respectively, which higher than ciprofloxacin with 0.625 mg/mL MIC. Antifungal potential investigated revealed MIC of 3.15, 6.25 and 12.5 mg/mL for Chry.A Al2O3 NP, Alm Al2O3 NP and Lam Al2O3 NPs against Candida albicans and Trichophyton rubrum. Therefore the use of novel extracts for the synthesis of Al2O3 NPs has demonstrated good antimicrobial activities when compared to the control standard.

Enhanced permanganate oxidation of phenolic pollutants by alumina and potential industrial application

In this study, we found that alumina (Al2O3) may improve the degradation of phenolic pollutants by KMnO4 oxidation. In KMnO4/Al2O3 system, the removal efficiency of 2,4-Dibromophenol (2,4-DBP) was increased by 26.5%, and the apparent activation energy was decreased from 44.5 kJ/mol to 30.9 kJ/mol. The mechanism of Al2O3-catalytic was elucidated by electrochemical processes, X-ray photoelectron spectroscopy (XPS) characterization and theoretical analysis that the oxidation potential of MnO4− was improved from 0.46 V to 0.49 V. The improvement was attributed to the formation of coordination bonds between the O atoms in MnO4− and the empty P orbitals of the Al atoms in Al2O3 crystal leading to the even-more electron deficient state of MnO4−. The excellent reusability of Al2O3, the good performance on degradation of 2,4-DBP in real water, the satisfactory degradation of fixed-bed reactor, and the enhanced removal of 6 other phenolic pollutants demonstrated that the KMnO4/Al2O3 system has satisfactory potential industrial application value. This study offers evidence for the improvement of highly-efficient MnO4− oxidation systems.

The Properties of Ultra-High-Performance Concrete with Assembly Unit of Secondary Aluminum Dross and Waste Fly Ash

Waste fly ash (WFA) and secondary aluminum dross (SAD) are common solid wastes inducing environmental pollution. These materials contain certain active substances that can be used in cement-based materials. Therefore, cement concrete can be used to solidify these solid wastes. In this study, the influence of the assembly unit of secondary aluminum dross (SAD) and waste fly ash (WFA) on the properties of ultra-high-performance concrete (UHPC) is investigated. The slump flow, the plastic viscosity, the yield shear stress, and the initial setting time of fresh UHPC are measured. Moreover, the flexural and compressive strengths and the dry shrinkage rate (DSR) are determined. The electrical resistance and reactance are tested. The electron microscopy spectroscopy (EDS), thermogravimetric analysis (TG), and X-ray diffraction spectrum (XRD) curves are obtained for revealing the mechanism of macroscopic performances. Results show that due to the optimal specific surface area and the volcanic ash effect, the UHPC with the assembly unit of 50% SAD and 50% WFA provides the highest slump flow, DSR, and mechanical strengths, while the corresponding plastic viscosity, yield shear stress, and electrical resistance are the lowest. The SAD can delay the setting time of UHPC. The relationship between the electrical resistance or the electrical reactance and the mass ratio of SAD accords with the quadratic function. The corresponding electrical resistance is the lowest. The relationship between the mechanical strengths and the electrical resistance fits with the cubic function. The leaching amounts of Zn and Cr increase in the form of cubic function with the immersing time. Meanwhile, the SAD can decrease the Zn and Cr by 0%–46.3% and 0%–45.2% respectively. As obtained from the EDS results, the element of Al is increased by adding SAD. The XRD curves show that the crystals of Al2O3 are increased and the SiO2 crystals are decreased by the added SAD. UHPC with 50% SAD exhibits the highest compact microstructures and the least Ca(OH)2 and 3CaO·SiO2 hydration products. The TG results show that UHPC with 50% SAD shows the lowest TG values of all the groups. This research will provide new UHPC materials and techniques applied in solidifying the WFA and SAD in the future.

Experimental evaluation of transition rate of sapphire crystal for thermal and fast neutrons using MNSR vertical neutron beam line

Using a perfect single crystal as a neutron filter allows us to have a thermal neutron beam with almost no background of fast neutrons. Single crystals of Al2O3 (sapphire) have proven to be effective filters for fast neutrons and are incorporated into neutron instruments. The present work would experimentally investigate c-axis neutron transmission rate by using different crystal thicknesses. In fact, the optimal thickness for sapphire filter is the one that maximizes the transmission of low energy neutrons and minimizes the transmission of fast neutrons, if there is no significant decrease in thermal neutron flux. In addition, neutron-filtering power of a-axis and c-axis sapphire crystals were compared with each other using different tests on a 2.5 cm slab of the sapphire crystals. The experimental tests were carried out by means of the available neutron flux top of the vertical neutron beam line of the Isfahan Miniature Neutron Source Reactor (MNSR) in two methods of foil activation and flux monitoring. In addition, the thermal and fast neutron dose rate reduction was discussed by using different thicknesses of the c-axis crystal.

Formation of mullite in fused cast AZS refractories

Fused cast refractories, based on the system Al2O3-ZrO2-SiO2 (AZS), are used in industrial glass tanks and are in direct contact with the glass melt and/or the furnace atmosphere (combustion gases, evaporation products, and dusts) at temperatures up to 1600 °C. Three samples of AZS materials were studied, (i) the original AZS refractory as delivered from the refractory industry, (ii) AZS refractory thermally treated similar to furnace heat up over days and ending for 10 h at 1580 °C and (iii) AZS refractory thermally cycled 600 times between 1530 and 1580 °C after furnace heat up simulation.The samples were studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) including Energy Dispersive X-ray analysis (EDX) and Electron Backscatter Diffraction (EBSD). In the untreated AZS, monoclinic ZrO2 (m-ZrO2) and Al2O3 were detected, while in AZS thermally treated at 1580 °C, mullite also occurred. Thermal cycling led to further increase in the mullite concentration and to a small concentration of tetragonal ZrO2 (t-ZrO2). The Al2O3 crystals as well as some of the ZrO2 had a blocky morphology. Surprisingly also formed mullite crystals were block and not needle-like. In the mullite as well as in the Al2O3 crystals tiny m-ZrO2 crystals were embedded which were formed during cooling in the production process from t-ZrO2 and were heavily twinned.

A comparison study on the dissolution mechanism of Al2O3 inclusion on fluorine-bearing and fluorine-free molten mold fluxes

The dissolution mechanism of Al2O3 inclusions in molten slags was explored by in-situ single hot thermocouple technique combined with X-ray photoelectron spectroscopy. Result shows that it takes 2940 s to completely dissolve Al2O3 inclusions in the molten F-bearing mold flux, which is mainly controlled by boundary layer diffusion. Because the connected [AlO6] octahedra in the Al2O3 inclusion is gradually destroyed by the O2− ions in the melt. By comparison, the CaO–SiO2–B2O3 based F-free mold flux only takes 840 s to completely dissolve Al2O3 inclusions. Because the [AlO6] octahedra is destroyed and further transformed to [AlO4] tetrahedra and produce O2− ions, which greatly facilitates the dissociation of the Al2O3 particle. However, the formed [AlO4] tetrahedra will promote the precipitation of the dense 2CaO·SiO2·Al2O3 crystals, which tightly encases the Al2O3 particle and causes significant drop in the dissolution rate. Thus, the dissolution rate is controlled by chemical reaction and then by boundary layer diffusion.

Similarities and differences in the interfacial microstructure and mechanical properties of alumina/alumina joints bonded with dysprosium- and neodymium-aluminosilicate glass filler

In this study, dysprosium-aluminosilicate (DAS) and neodymium-aluminosilicate (NAS) glasses with high softening temperature were used as fillers to join alumina ceramics. The similarities and differences in the interfacial microstructure and flexural strength of the joints were investigated. Results showed that the glass fillers both could infiltrate into alumina ceramics during the joining process. However, excessive infiltration at high joining temperatures led to the formation of pore defects in the brazing seam. An interfacial reaction layer composed of Dy3Al5O12 was formed at the DAS glass/alumina interface. In contrast, no interfacial reaction was observed between the NAS glass and alumina ceramic. Slower cooling rate promoted the crystallization of Dy2Si2O7 and Al2O3 in the Al2O3/DAS/Al2O3 joints, and only Nd2Si2O7 in the Al2O3/NAS/Al2O3 joints. The flexural strength at room temperature of both joints first increased and then decreased with the increased of joining temperature, and showed a declined tendency with the decrease in cooling rate. The flexural strength at 900 °C of Al2O3/DAS/Al2O3 joints reached 245 MPa, which is higher than that of Al2O3/NAS/Al2O3 joints.

Selectively Tuning the Substrate Adhesion Strength of Aligned Carbon Nanotube Arrays via Thermal Postgrowth Processing.

The excellent intrinsic properties of aligned nanofibers, such as carbon nanotubes (CNTs), and their ability to be easily formed into multifunctional 3D architectures motivate their use for a variety of commercial applications, such as batteries, chemical sensors for environmental monitoring, and energy harvesting devices. While controlling nanofiber adhesion to the growth substrate is essential for bulk-scale manufacturing and device performance, experimental approaches and models to date have not addressed tuning the CNT array-substrate adhesion strength with thermal processing conditions. In this work, facile "one-pot" thermal postgrowth processing (at temperatures Tp = 700-950 °C) is used to study CNT-substrate pull-off strength for millimeter-tall aligned CNT arrays. CNT array pull-off from the flat growth substrate (Fe/Al2O3/SiO2/Si wafers) via tensile testing shows that the array fails progressively, similar to the response of brittle microfiber bundles in tension. The pull-off strength evolves nonmonotonically with Tp in three regimes, first increasing by 10 times through Tp = 800 °C due to graphitization of disordered carbon at the CNT-catalyst interface, and then decreasing back to a weak interface through Tp = 950 °C due to diffusion of the Fe catalyst into the substrate, Al2O3 crystallization, and substrate cracking. Failure is observed to occur at the CNT-catalyst interface below 750 °C, and the CNTs themselves break during pull-off after higher Tp processing, leaving residual CNTs on the substrate. Morphological and chemical analyses indicate that the Fe catalyst remains on the substrate after pull-off in all regimes. This work provides new insights into the interfacial interactions responsible for nanofiber-substrate adhesion and allows tuning to increase or decrease array strength for applications such as advanced sensors, energy devices, and nanoelectromechanical systems (NEMS).

Numerical Analysis of Dislocation Density of c ‐, a ‐, m ‐axes Grown Al 2 O 3 Crystals during Annealing Process

A numerical study of dislocation density is carried out by 3D and time-dependent analysis using the Alexander–Haasen model to estimate growth direction dependence of plastic deformation of Al2O3 single crystals during the annealing process. The direction of crystal growth is set to c-, a-, and m-axes. The calculated results show distribution of dislocation density in the crystal grown in the c-axis has a sixfold symmetry while those in the crystals grown in the a- and m-axes show asymmetric distribution. Dislocation densities in the a- and m-axes Al2O3 crystals are larger than that in the c-axis crystal.

Control of multiphase evolution and Al-deficiency in reactive-sintered MoAlB ceramics with excessive Al

MoAlB is a ternary boride of MAB phases with strong resistance to oxidation and ablation at service temperature, thanks to preferential Al diffusion to form a protective oxide scale. However, excessive Al were often necessary in sintering of MoAlB ceramics, suggesting that a liquid-phase densification might occur thus leading to complex microstructures. By quantitative SEM analysis, ~17 mol.% Al2O3 phase was found common in MoAlB ceramics. The liquid-phase of Al-Mo-B-O facilitates the direct conversion from MoB to MoAlB before in situ formation of Al2O3. An intermediate Mo3Al8 phase competes with layered conversion, which limits the insertion rate of Al into B-B layers of MoB to form abundant Al-deficient stacking-faults. Intermetallic Mo3Al8 phase precipitates further in the intergranular regions parallel to the crystallization of Al2O3, leaving the reprecipitation of remaining Al. Both layered-conversion and intergranular oxides can improve ablation behavior for MoAlB ceramics, as well as fracture toughness and compressive strength.

Characterization of structural orientation and optical properties of Al and Cr in rubies

We study the correlation between the structural orientation and the chromatic characteristics in rubies by combining X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and density functional theory (DFT) calculations. The chemical compositions were investigated by X-ray fluorescence (XRF). XRD result shows the preferred orientation of Al2O3 crystals as the (113), (110), and (223) plans. The local site and structural orientation of Cr impurities were investigated by the XAS technique, which prefers [141] and [411] polarizations. The optical absorption energy was estimated according to UV–visible spectroscopy. The results show the impurity state that relates to the optical absorption and emission energies. More importantly, the results show that the information on the locally determined structures and their effect on energy levels in rubies were obtained and discussed.

Erbium ion implantation into LiNbO3, Al2O3, ZnO and diamond - measurement and modelling - an overview.

The presented overview deals with the study of the luminescence properties of lanthanide ions incorporated into different dielectric crystalline materials for use in photonics and optoelectronics. From the crystalline materials, non-centrosymmetric hexagonal crystals of LiNbO3, Al2O3 and ZnO, together with the centrosymmetric cubic crystal of diamond, were chosen. The above-mentioned materials represent a certain cross-section through various crystal structure geometries with different internal bonding of atoms which represent different crystal vicinity for the incorporated Er ions. During more than ten years of our research, each of the crystals was doped with erbium ions and the resulting structural and luminescence properties were studied in detail and compared between the mentioned crystalline materials to find similar behaviour for erbium ions in the different crystalline materials. To better understand the incorporation of erbium in the studied crystalline materials, theoretical simulations of different erbium-doped crystal models were carried out. In the calculations, cohesive energies of the structures and erbium defect-formation energies were compared in order to find the most favourable erbium positions in the crystals. Also, from the geometry optimization calculations, the optimal geometry arrangements in the vicinity of erbium ions in different crystals were studied and visualized. The results of the theoretical simulations confirmed the experimental results - i.e., from all the theoretical erbium-doped crystal models, the most stable structures contained erbium in the substitutional positions with octahedral oxygen coordination.

Electronic ionisation-induced annealing of pre-existing defects in Al2O3 and CaF2 single crystals

ABSTRACT Electronic ionisation-induced annealing of pre-existing defects in CaF2 and Al2O3 single crystals has been investigated. Pre-existing defects (vacancies and interstitials) and defect aggregates were first induced in both crystals by fast neutrons irradiation and then irradiated by 90 MeV Xe ions. After irradiation, the samples were characterized using Doppler Broadened Emission Spectroscopy (DBS). The S parameter and average S values obtained for the neutrons irradiated samples are compared with results obtained for samples irradiated by neutrons + Xe ions. Results of these experiments revealed ionisation-induced pre-existing defect annealing in Al2O3 while generating more defects in CaF2. It is also found that the defect recovery rate in Al2O3 crystal depends on the Xe ions fluence that confirms the different mechanisms of defect formation in both materials. The electronic ionisation and excitation energy are transferred to the defects formation in the self-trapped exciton (STE) mechanism resulting in defect formation in CaF2. Whereas in the case of Al2O3, it is transferred to electron–phonon coupling leading to lattice heating, which causes the annealing of the pre-existing defects.

IRIXS Spectrograph: an ultra high-resolution spectrometer for tender RIXS.

The IRIXS Spectrograph represents a new design of an ultra-high-resolution resonant inelastic X-ray scattering (RIXS) spectrometer that operates at the RuL3-edge (2840 eV). First proposed in the field of hard X-rays by Shvyd'ko [(2015), Phys. Rev. A, 91, 053817], the X-ray spectrograph uses a combination of laterally graded multilayer mirrors and collimating/dispersing Ge(111) crystals optics in a novel spectral imaging approach to overcome the energy resolution limitation of a traditional Rowland-type spectrometer [Gretarsson et al. (2020), J. Synchrotron Rad. 27, 538-544]. In combination with a dispersionless nested four-bounce high-resolution monochromator design that utilizes Si(111) and Al2O3(110) crystals, an overall energy resolution better than 35 meV full width at half-maximum has been achieved at the Ru L3-edge, in excellent agreement with ray-tracing simulations.

Time-resolved high energy ionoluminescence of Al2O3

We have compared the luminescence decay from intact and pre-damaged Al2O3 crystals registered during single swift heavy ion and photo- picosecond laser pulse excitation (λex. = 440 nm). The decay curves measured during 1.2 ÷ 1.6 MeV/amu C, Ar, V, Kr, Xe ion irradiation at room temperature are composed of three components – fast (τ1 < 1 ns), τ2 = 1.8 ns (F+-centers) and τ3 = 54–80 ns (E-luminescence, the nature of emission is under discussion). The measurements performed on pre-irradiated samples have demonstrated that accumulated radiation damage suppresses the E-luminescence and only τ1 and τ2 components are observed.It was found that photoexcitation at 440 nm induces strong emission of F22+- centers with a lifetime of about 8 ns which is not detected during high energy ion irradiation. This is ascribed to the quenching effect of high density excitations in a particle track.