Pulsed Cathodoluminescence Spectra Research Articles

Sintering and characterization of novel multilayered MgAl2O4/YAG, MgAl2O4/YSZ and YAG/YSZ ceramic-ceramic architectures for photonic applications

During layer-by-layer formation of Y3Al5O12 (YAG), MgAl2O4 (MAS), ZrO2–Y2O3 (YSZ) powders and their consolidation by the SPS method, multilayer YAG/MAS, YSZ/YAG and MAS/YSZ ceramics exhibiting functionally graded properties were synthesized. The morphological, mechanical, optical and luminescent properties have been studied in detail for fabricated ceramics. It is shown that the microhardness of both the ceramics layers and the separate single layers are comparable to each other. The transmission spectra of YSZ/YAG and YAG/MAS ceramics showed correlation with the transmission level prepared from monolayers of starting materials. For MAS/YSZ, this agreement was not found. It has been shown that the pulsed cathodoluminescence spectra of YSZ/YAG, YAG/MAS, and MAS/YSZ with a good agreement of existing luminescence centers nature for YAG, YSZ, and MAS multilayer ceramics. This work provides promising new microstructures in developing novel multilayered luminescent ceramics for photonic applications.

Express Synthesis of YAG:Ce Ceramics in the High-Energy Electrons Flow Field.

YAG:Ce ceramics by the direct action of an electron beam with 1.4 MeV energy were synthesized on a mixture of a stoichiometric composition of Y, Al, and Ce oxides without adding any substances to facilitate the process. The synthesis is realized in a time less than 1 s. The main structural phase of the obtained ceramics is YAG and YAP can be additional. The luminescence characteristics of the synthesized samples, the excitation, luminescence, decay time, and pulsed cathodoluminescence spectra, are similar to those known for YAG:Ce phosphors. The conversion efficiency of the excitation energy into the luminescence of the samples reaches 60-70% of those used for the manufacture of LED phosphors. The set of processes that determine the rate and efficiency of radiation synthesis differs from those occurring during thermal methods by the existence of a high degree of the initial compositions' ionization under the influence of a radiation flux and a high probability of the decay of electronic excitations into short-lived radiolysis products.

Synthesis and spectroscopic properties of aluminum oxynitride doped with 3d-metal ions: The case of γ-AlON:Ti

Polycrystalline samples of γ-aluminum oxynitride (Al5O6N) doped with titanium ions have been prepared via high temperature annealing of mixtures of AlN, Al2O3 and TiO2. Electronic structure and spectroscopic properties of AlON:Tin+ were studied for the wide range of Tin+ concentrations varying from 0.05 to 5.0 at% vs. aluminum. The solubility limit of Tin+ ions in Al5O6N can be estimated at the level of 0.2–0.5 at% and an excess of Tin+ forms TiN phase. Following the XPS data, titanium exists in three different coordination environments including [TiO6], [TiOxN6–x] and [TiN6]. The optical gap evaluated from the diffuse reflectance spectra is consistent with the earlier defined for γ-AlON and shows the tendency to decrease at higher titanium content. Pulsed cathodoluminescence spectra show several bands originating from intrinsic and impurity defects. The titanium doping of γ-AlON results in overall reducing of optical and luminescence properties.

Properties of Compacts from Mixtures of Calcium Fluoride Micro- and Nanopowders

In this work, compacts from mechanical mixtures of CaF2 micron powder (MCP) with CaF2 nanopowder (NP) additives were produced, with mass ratios of the mixture components ranging from 10:0.125 to 10:1, respectively, using magnetic pulse (MP) and static pressing (SP) methods. The effects of pressure (Pp) and pressing temperature (Tp), concentration and phase composition of the additive on the density and color of compacts were studied, taking into account the properties of the initial components of the mixtures. The evolution of pulsed cathodoluminescence (PCL) spectra and photoluminescence (PL) of compacts from pure powders and their mixtures depending on Pp, Tp and characteristics of initial CaF2 NP was also studied. A new near-infrared (NIR) band associated with fluoride vacancies was discovered with a maximum at ~765 nm in PCL spectra of compacts produced by MP at a temperature of 425 °C. A blue band at 435 nm associated with impurity oxygen vacancies in the CaF2 lattice was found in PL spectra compacts of pure NP and powder mixtures. The density of compacts of pure NP and MCP reached 89% of the theoretical density, and the density of compacts of mixtures did not exceed 78%. The defective structure and phase composition of the CaF2 NP had a decisive effect on the luminescent properties of compacts from mixtures of micro- and nanopowders.

Luminescence response of neodymium ions to phase transformations in yttria-based solid-solution nanopowders

Subject of study. In this paper, we describe the luminescence properties of nanopowders of composition (Nd0.008Y0.992)2O3, (Nd0.008Y0.992)2O3+6mol%ZrO2, and (Nd0.008Gd0.496Y0.496)2O3+5mol.%ZrO2 with various percentages of monoclinic and cubic phases. Method. Photoluminescence and pulsed cathodoluminescence spectra are recorded, followed by interpretation of the results obtained. Main results. In the process of studying the luminescence bands corresponding to the 4F3/2→4I9/2 and 4F3/2→4I11/2 energy transitions for neodymium ions in nanopowder crystalline lattices, we identify several spectroscopic and kinetic properties that can be used to identify the substances and determine the crystal phases present. We show that there is slight broadening of the spectral lines in the continuum base of the 4F3/2→4I11/2 manifold; the intensity level below which the bands merge into a continuum increases as the amount of structural disorder caused by the zirconium- and gadolinium-ion dopants in the Y2O3 increases. Practical significance. The distinctive features of the photoluminescence spectra and the kinetics of neodymium-ion luminescence in the 4F3/2→4I9/2 and 4F3/2→4I11/2 bands can be used for unique identification of the substances present and determination of the crystal phases thereof; this will be of practical interest in the development of high-bandwidth ceramic active elements.

ZnS Nanopowders and ZnS/Ag2S Heteronanostructures: Synthesis and Properties

Zinc sulfide ZnS nanopowders were prepared by chemical deposition from aqueous solutions of zinc nitrate and sodium sulfide in the presence of sodium citrate or Trilon B. ZnS/Ag2S heteronanostructures were prepared by two-step chemical codeposition of zinc and silver sulfides. The prepared ZnS nanopowders had average particle sizes ranging from 2 to 10 nm depending on the reagent concentration ratio in the batch. The nanoparticle sizes in the thus-prepared heteronanostructures were 8–10 nm. The diffuse reflectance spectra of nanostructured ZnS and ZnS/Ag2S heteronanostructures were measured. The bandgap width Eg in the studied sulfide nanostructures was assessed based on an examination of the measured optical absorption spectra. As the nanoparticle size decreased from 10 to 2 nm, the Eg in ZnS nanopowders increased in the range 3.59–3.72 eV. The increasing Ag2S percentage in ZnS/Ag2S heteronanostructures leads to narrowing of the bandgap. Pulsed cathodoluminescence (PCL) spectra were recorded. The luminescence characteristics of ZnS and ZnS/Ag2S depend on the preparation method and nanoparticle morphology.

Intrinsic defects and their influence on optical properties of ALa9(GeO4)6O2 (A = Li, Na, K, Rb, Cs) oxyapatites prepared by spray pyrolysis

Abstract New germanate ALa9(GeO4)6O2 (A = Li, Na, K, Rb, Cs) oxyapatites, showing promise as host lattices for phosphors with emission in the visible and infrared spectral ranges, have been obtained for the first time by ultrasonic spray pyrolysis. The discussion is focused on native defectiveness and optical properties of these compounds, depending on the nature of alkaline ions. Spray pyrolysis method was consciously used to obtain the compounds with intrinsic defects as confirmed by electron paramagnetic resonance. Reviewing available EPR data, the registered EPR response was assigned to the paramagnetic centers related to germanium tetrahedra embracing the oxygen vacancies. According to quantum-chemical calculations the oxygen-deficient centers in ALa9(GeO4)6O2 are presumably stabilized by antisite defects in the cation sublattice. Diffuse reflectance and pulse cathodoluminescence spectra of the compounds were investigated in detail, establishing a distinct dependence of optical properties on the type of alkaline ion. The observed optical absorption maxima at 275 and 370 nm were attributed to the F-like centers. The inverse dependence of luminescence intensity on the degree of defectiveness was interpreted on the assumption that these centers were involved in non-radiative energy relaxation.

Luminescence of impurity and intrinsic defects of Na-doped alumina ceramic

Ceramics from alumina nanopowder doped with a different Na concentration were synthesized at high-temperature sintering under vacuum and in air at a varying temperature. Pulsed cathodoluminescence spectra and thermoluminescence curves were measured to study effects based either on the formation of new defects or on the modification of alumina intrinsic defects. In fact, the emission bands with maxima of 400, 510 and 693 nm are recorded on pulsed cathodoluminescence spectra of Al2O3:Na ceramics, which are respectively responsible for their intrinsic centers of alumina (F-centers), Na and Cr impurity centers. A decrease in the synthesis temperature results in an increase in the intensity of the 510 nm band. Sodium impurity concentration growth in ceramics results in the intensity growth of the given band. It is also shown that an increase in the sintering temperature causes an increase in the intensity of all thermoluminescence peaks. Thermoluminescence curves are also changed under β-irradiation.

New luminescent ceramics based on anion-deficient Al2O3–BeO for high-dose dosimetry

New Al2O3–BeO ceramics were synthesized by using high-temperature treatment of the initial compacts of nanostructured alumina in BeO crucible. The decomposition of the pulsed cathodoluminescence spectra into Gaussians revealed the luminescence bands related to oxygen vacancies and their aggregates in the ceramics. TL of the synthesized ceramics exposed to high-dose irradiation contained three peaks at 360 (A), 525 (B) and 730 K (C). It was found that optical stimulation at the wavelength of 470 nm causes optical bleaching of the traps responsible for peaks A and B, in contrast to the deep traps of the peak C, and gives rise to OSL. At the same time, there was a shift of the position of peaks A and B to the high-temperature region. This result shows the presence of the energy distribution of the traps responsible for TL peak A. It was found that the range of linearity of the TL dose response after gamma-irradiation is from 0.01 to 1.0 kGy. After irradiation with a pulsed electron beam (130 keV), the linear behavior of the OSL dose response was observed from 3 to 30 kGy.

P5+ Ion Doped Gd2SiO5:Ce3+ Scintillation Crystal

Ce3+, P5+, Ca2+, and Zn2+ ion doped Gd2SiO5 crystals are grown by the Czochralski method. The pulsed cathodoluminescence spectra, light yield, and scintillation time under gamma excitation are studied. It is first shown that additional doping with P5+ phosphorus ions decreases crystal cracking in the fabrication of scintillation elements, and increases the scintillation light yield in comparison with commercial Gd2SiO5:Ce3+ crystals.

Synthesis and Luminescence Properties of Tb3+-Doped Aluminum Oxynitride

We report an experimental study concerned with the synthesis and luminescence properties of Al5O6N aluminum oxynitride doped with Tb3+ in the concentration range 0.025–0.5 at %. All of the samples, prepared by firing appropriate mixtures in a nitrogen atmosphere at 1600°C, consisted predominantly of phase-pure γ-ALON (Al5O6N), with small amounts of impurity phases: Al7O3N5 aluminum oxynitride and Tb3Al5O12 terbium aluminate. Their pulsed cathodoluminescence and photoluminescence spectra contain emission bands typical of Tb3+ ions. The concentration threshold for luminescence quenching corresponds to a Tb3+ concentration at a level of 0.4 at %. A Tb3+ cross relaxation effect found in Al5O6N:Tb3+ is discussed and photoluminescence spectra are shown to be inhomogeneous at low Tb3+ concentrations in Al5O6N.

Intrinsic luminescence of CaF2 crystals under simultaneous excitation of pulsed accelerated electrons and stimulated emission of semiconductor CdSSe

Nominally pure CaF2 crystals were grown by Stockbarger method. Pulse cathodoluminescence (PCL) spectra were studied. PCL spectra of CaF2 crystals at room temperature were excited by pulse of accelerated electrons and simultaneous stimulated emission of CdSSe crystal. It was shown that the simultaneous excitation of the crystals CaF2 leads to a reduction efficiency of creation of self-trapped excitons (STEs) and the appearance of short-lived emission in the UV region of the spectrum.

Scintillation Properties of Oxyorthosilicate Crystals Gd2SiO5:Ce3+:Ca2+

Scintillation single crystals and polycrystals of gadolinium oxyorthosilicate Gd2SiO5: Ce3+,Ca2+ are grown by the Czochralski method. The effect of the doping ion concentration on pulsed cathodoluminescence spectra, light output, and scintillation time under gamma excitation is studied. It is shown that the scintillation time decreases with increasing both Ce3+ and Ca2+ ion concentrations.

Properties of compacts of barium fluoride nanopowder produced by pulsed electron beam evaporation

Abstract Mesoporous crystalline BaF 2 nanopowder with a specific surface area of up to 34.8 m 2 /g was produced by a pulsed electron beam through the evaporation of targets of micro-sized BaF 2 powder with optical purity ( S red = 0.38 m 2 /g). The texture and thermal features of the BaF 2 nanopowder (before and after annealing in air at a temperature of 200 °C) and some properties of compacts made of the BaF 2 nanopowder by magnetic-pulse compaction and static pressing were studied. Glassy, opaque, and black compacts, which are promising materials for use as scintillators and dosimeters, were produced by magnetic-pulse compaction in a vacuum at a temperature of about 425 °C. It was found that heating up to 425 °C is sufficient for removing defects in nanopowders. The effect of pressing methods on the pulsed cathodoluminescence and photoluminescence spectra of the compacts was studied. Luminescent properties were found to depend on pressing technology. It was also determined that surface color centers, the number of which decreases during heating, are responsible for the pulsed cathodoluminescence band near ∼560 nm.

Cherenkov Radiation in the Visible and Ultraviolet Spectral Ranges from 6-MeV Electrons Passing through a Quartz Plate

Cherenkov radiation and pulsed cathodoluminescence spectra in the ultraviolet, visible, and near infrared regions generated by a 6-MeV electron beam passing through GE-014 and KU1 quartz plates have been experimentally studied. The Cherenkov radiation spectrum has been recorded in the ultraviolet and visible regions and its change is shown at the variation of the angle between the plane of the plate and the direction of the electron beam. The data on the conditions of recording of the Cherenkov radiation spectra at the excitation of plane-parallel plates of quartz, sapphire, and diamond have been presented. It has been shown that the total internal reflection in the crystals with a high refractive index imposes certain conditions on the geometry of the output of Cherenkov radiation into vacuum at electron energies above 500 kev.

Luminescence Quenching in Magnesium-Doped Alumina Ceramics

The effect of magnesium impurity on luminescent properties of alumina ceramics sintered at high temperatures under vacuum is studied by pulsed cathodoluminescence, photoluminescence, and thermoluminescence. At dopant concentrations >1 wt %, high-temperature synthesis results in formation of defects associated with magnesium, which were identified in the pulsed cathodoluminescence (520 nm) and photoluminescence (767 nm) spectra, as well as in the thermoluminescence curves (380 K). It is found that increased magnesium concentration leads to luminescence quenching of the intrinsic centers (F centers) of alumina in the PCL emission band at 400 nm, impurity defects (Mn4+ and Cr3+) in the photoluminescence emission bands at 673 and 689 nm, and all the recorded thermoluminescence peaks at 380, 450, and 615 K.

The influence of magnesium doping on luminescent and dosimetric properties of alumina ceramics

Alumina ceramics doped with a different concentration of magnesium ions were synthesized at high-temperature sintering under vacuum and in air. Pulse cathodoluminescence spectra and thermoluminescence curves have been measured to evaluate the influence of a dopant concentration on luminescent and dosimetric properties of alumina ceramics. An increase in the magnesium concentration leads to an increase in the pulse cathodoluminescence intensity of the 520 nm band and in the thermoluminescence intensity of all peaks with the maxima of 360, 460 and 620 K. A superlinear increase in the thermoluminescence intensity with a growing dose is observed in the range of 1.5–150 Gy for the peak at 620 K.

Synthesis and optical properties of Tb3+ or Dy3+-doped MgAl2O4 transparent ceramics

MgAl2O4 ceramics doped with rare earth ions (Tb3+ and Dy3+ ions) were fabricated by SPS technique. Optical properties and pulse cathodoluminescence (PCL) spectra were studied. The redshift effect of the absorption boundary for rare earth (RE) ions doped ceramics was shown. It was shown that cathodoluminescence spectra in nanosecond time range can be decomposed into several emission bands at 2.72, 3.01, 3.37, 3.63 eV caused by F-type centers. It has been demonstrated that the introduction of terbium and dysprosium ions practically does not change the intensity ratio of the bands at 2.72, 3.01, 3.37 eV, but leads to an increase in the band at 3.63 eV in nanosecond time range. There are emission bands related to intrinsic host defects, RE ions dopants (Dy3+, Tb3+), and trace elements (Cr3+ ions) in PCL spectra measured in millisecond time range. The dependences of kinetic characteristics of spinel ceramics were studied. In nanosecond time range, decay kinetics of the MAS ceramics is described by the sum of two exponentials with luminescence decay times are 30 ± 5 ns and 0.8 ± 0.1 μs In the millisecond time interval, the luminescence decay time depends on the dopant ions.

Energy conversion in LiSrPO4 doped with Pr3+ ions

We report on the time-resolved luminescence spectroscopic characterization of LiSrPO4 doped with Pr3+ ions, that we found potentially attractive for scintillation applications. The spectroscopic study included measurements of photoluminescence, X-ray excited luminescence, thermally stimulated luminescence and time-resolved pulse cathodoluminescence spectra. In addition, luminescence decay kinetics were studied upon high-frequency X-ray and pulse cathode beam excitation. LiSrPO4:Pr3+ showed Pr3+ emission connected with intraconfigurational 4f2→4f2 and interconfigurational 4f15d→4f2 transitions. The presence of defects was shown with thermoluminescence measurements and suggested to be the main reason for delayed recombination of charge carriers on Pr3+ 4f15d states. Some peculiarities of host-to-impurity energy transfer are discussed.

Тушение люминесценции в керамиках оксида алюминия допированных магнием

AbstractThe effect of magnesium impurity on luminescent properties of alumina ceramics sintered at high temperatures under vacuum is studied by pulsed cathodoluminescence, photoluminescence, and thermoluminescence. At dopant concentrations >1 wt %, high-temperature synthesis results in formation of defects associated with magnesium, which were identified in the pulsed cathodoluminescence (520 nm) and photoluminescence (767 nm) spectra, as well as in the thermoluminescence curves (380 K). It is found that increased magnesium concentration leads to luminescence quenching of the intrinsic centers ( F centers) of alumina in the PCL emission band at 400 nm, impurity defects (Mn^4+ and Cr^3+) in the photoluminescence emission bands at 673 and 689 nm, and all the recorded thermoluminescence peaks at 380, 450, and 615 K.