Transparent alumina doped with rare‐earth or transition metal oxides represents a group of materials suitable for optical applications. Because of the birefringence of alumina, their preparation is ...demanding on the quality of starting materials, their advanced shaping, and pressure‐assisted sintering. Spark plasma sintering and hot isostatic pressing have proven at achieving pore‐free fine microstructures exhibiting high in‐line transmission and a sufficient intensity of emitted light. The present review aims to summarize the results published on this topic, to compare them and on this base to propose other possible and/or appropriate approaches to future.
The effect of Yb3+ co‐doping on relaxation dynamics of excited states of Er3+ ion in oxyfluoro tellurite (TZYN) glasses was demonstrated employing excitation and luminescence spectroscopy. The ...up‐conversion luminescence spectra were studied as a function of temperature in the 298–633 K range, and fluorescence intensity ratio (FIR) for green bands due to the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+ ion against temperature was determined. The temperature sensing performance of TZYN:Er3+/Yb3+ glasses was studied using the FIR technique up to 633 K. The maximum absolute (Sa) and relative (Sr) sensitivity of 0.00246 K−1 at 413 K and 0.72% K−1 at 323 K, respectively, were determined for TZYN:0.5Er3+ /1.0 Yb3+ glass.
Abstract
The optical characteristics of Dy
3+
-doped phosphate and borophosphate glasses with different divalent network modifiers prepared by melt-quenching are studied. The glass sets (A) with a ...molar composition of 40MO–60P
2
O
5
and (B) with a molar composition of 40MO–20B
2
O
3
–40 P
2
O
5
are investigated, both with M = (Zn
2+
, Mg
2+
, Ca
2+
, Sr
2+
, or Ba
2+
) and all doped with 0.1 mol% Dy
2
O
3
. Raman and fluorescence spectroscopy are used to analyse the structure and optical characteristics of these glasses. Four typical Dy
3+
emission bands in the yellow (572 nm), blue (483 nm) and red (633 and 752 nm) regions of the spectrum are observed in both sets. The fluorescence lifetimes in each glass set are correlated to the network modifier's ionic field strength. The Mg
2+
and Zn
2+
containing glasses have the longest fluorescence lifetimes. The yellow to blue emission intensity ratio of the respective bands can be used to indicate a symmetric environment around Dy
3+
ions and varies with the ionic field strength of the modifier cations: a higher ionic field strength leads to a higher yellow to blue ratio, which in turn indicates a higher asymmetrical local coordination environment of Dy
3+
ions in the glassy host network.
Abstract
The origin of the bright and hard X-ray emission flux among the
γ
Cas subgroup of B-emission line (Be) stars may be caused by gas accretion onto an orbiting white dwarf (WD) companion. Such ...Be+WD binaries are the predicted outcome of a second stage of mass transfer from a helium star mass donor to a rapidly rotating mass gainer star. The stripped donor stars become small and hot white dwarfs that are extremely faint compared to their Be star companions. Here we discuss model predictions about the physical and orbital properties of Be+WD binaries, and we show that current observational results on
γ
Cas systems are consistent with the expected large binary frequency, companion faintness and small mass, and relatively high mass range of the Be star hosts. We determine that the companions are probably not stripped helium stars (hot subdwarf sdO stars), because these are bright enough to detect in ultraviolet spectroscopy, yet their spectroscopic signatures are not observed in studies of
γ
Cas binaries. Interferometry of relatively nearby systems provides the means to detect very faint companions including hot subdwarf and cooler main-sequence stars. Preliminary observations of five
γ
Cas binaries with the CHARA Array interferometer show no evidence of the companion flux, leaving white dwarfs as the only viable candidates for the companions.
Highly transparent Dy3+ and Dy3+/Cr3+ polycrystalline alumina ceramics were prepared with the real in-line transmittance (RIT) up to 55% (at λ = 632 nm), one of the highest values reported for ...luminescent rare-earth elements doped alumina. The RIT of doped alumina decreased more sharply with increasing mean grain size than predicted by the models for pure alumina. Co-doping with Dy3+ and Cr3+ resulted in a moderate increase of the RIT, which was independent on grain size. EDX analysis revealed that dysprosium segregated at grain boundaries and chromium was dispersed throughout the alumina matrix. A thermodynamic model for diffusion of multiple species in systems with multiple sorts of traps was proposed. The photoluminescence excitation and emission spectra of Dy3+-doped alumina showed peaks characteristic for Dy3+-doped materials. In co-doped Dy3+/Cr3+ alumina, Dy3+ emitted in the blue and yellow regions and Cr3+ in the red region, creating a suitable combination for obtaining white light.
We report on successful preparation of Er3+ doped transparent alumina (0.1–0.17 at.%) exhibiting visible light photoluminescence using wet shaping method and hot isostatic pressing. The effects of ...dopant amount, type of doping powder and powder pre-treatment on final microstructure, real in-line transmittance and photoluminescence characteristics were studied.
The real in-line transmittance ranged between 28 and 56%, depending on processing parameters. The transparency decreased with increased amount of dopant. The decrease is dependent on the type of doping powder and its pre-treatment.
The photoluminescence spectra measured in both visible and NIR region showed typical emission bands due to the presence of Er3+ ions. The decay profiles of the 4S3/2→4I15/2 transition were fitted with a 2-exponential function, with faster component in the range of 360–700ns and slower component around 1.6-2.4μs. The intensity of emissions and lifetime of the 4S3/2 level decrease significantly with increasing concentration of Er3+ ions.
Abstract Rapid rotation and nonradial pulsations enable Be stars to build decretion disks, where the characteristic line emission forms. A major but unconstrained fraction of Be stars owe their rapid ...rotation to mass and angular momentum transfer in a binary. The faint, stripped companions can be helium-burning subdwarf OB-type stars (sdOBs), white dwarfs (WDs), or neutron stars. We present optical/near-infrared Center for High Angular Resolution Astronomy (CHARA) interferometry of 37 Be stars selected for spectroscopic indications of low-mass companions. From multiepoch H - and/or K -band interferometry plus radial velocities and parallaxes collected elsewhere, we constructed 3D orbits and derived flux ratios and absolute dynamical masses of both components for six objects, quadrupling the number of anchor points for evolutionary models. In addition, a new wider companion was identified for the known Be + sdO binary 59 Cyg, while auxiliary Very Large Telescope Interferometer/GRAVITY spectrointerferometry confirmed circumstellar matter around the sdO companion to HR 2142. On the other hand, we failed to detect any companion to the six Be stars with γ Cas–like X-ray emission, with sdOB and main-sequence companions of the expected spectroscopic mass being ruled out for the X-ray-prototypical stars γ Cas and π Aqr, leaving elusive WDs as the most likely companions, as well as a likely explanation of the X-rays. No low-mass main-sequence close companions were identified for the other stars.
The ytterbium-aluminate microspheres with yterbium-aluminium garnet composition doped by 0.25, 0.5, 0.75, 1.0, 3.0 and 5.0 mol.% of Er2O3 were prepared by combination of sol-gel method and flame ...synthesis. The prepared systems were mostly X-ray amorphous with the presence of traces of ytterbium-aluminium garnet phase (YbAG), and ytterbium oxide. The thermal analysis of prepared systems shows crystallization of the prepared systems in the temperature interval 914–984 °C in one or two steps, depending on the Er content. Ytterbium aluminate garnet was found to crystallize as the prevailing phase in all heat-treated samples. An almost pure red up-conversion photoluminescence emission with the intensity influenced by the Er2O3 content was observed in prepared systems.
Present work is focused on the preparation of bulk glass with stoichiometric yttrium aluminium garnet (YAG) composition, which has high tendency to crystallize. Glass microspheres were prepared by ...flame synthesis from sol-gel prepared YAG precursor. Sintering conditions in SPS apparatus such as heating rate, pressure and temperature were optimized with the aim to prepare transparent material. Results revealed that glass with high tendency to crystallize is very sensitive to time of densification under load (associated with the maximum applied temperature). The increase of the pressure led to the expansion of the translucent part of the sample. Dense, and slightly translucent amorphous samples (total transmission measured at 550 nm was 4.8 %) were successfully prepared by viscous flow SPS sintering of glass microspheres at temperatures below 910 °C without any isothermal dwell.
Transparent oxyfluoride glass-ceramics (GCs) with embedded β-Na1.5Y1.5F6 crystals doped with Er3+ ions were fabricated by a melt-quenching method with subsequent heat-treatment. The structural ...characterizations and spectroscopic techniques were performed to verify the precipitation of β-Na1.5Y1.5F6 crystals and partition of the Er3+ dopant into the crystals. Bright green up-conversion (UC) emission was achieved in Er3+-doped glass-ceramic (Er-GC). Furthermore, the temperature-dependent visible UC behavior based on thermally coupled energy levels (TCLs) and non-thermally coupled energy levels (NTCLs) was also examined in the temperature range 298 k to 823 K with maximum relative sensitivity (Sr) of 1.1% K−1 at 298 K for TCLs in Er-G and Er-GC samples.
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