Spectroscopic investigation and optical characterization of novel highly thulium doped tellurite glasses

In this paper, optical properties of 75TeO₂-20ZnO-5Na₂O host glass doped with concentration of Tm³⁺ up to 10 %mol were studied in order to assess the most suitable rare earth content for short cavity fiber lasers. Raman spectroscopy revealed a change in the glass structure while increasing Tm³⁺ content, similar to the well known addition of alkali ions in a glass. Influence of the fabrication process on the OH⁻ content was determined by FTIR measurements. Refractive index of Tm³⁺ doped tellurite glasses was measured at five different wavelengths ranging from 533 nm to 1533 nm. Lifetime and emission spectra measurements of the Tm³⁺ doped tellurite glasses are reported.     

Incorporation of silver into soda-lime silicate glass by a classical staining process

Silver was introduced into soda-lime silicate glass by a classical staining process under varying conditions of temperature and time. The spectroscopic features of the stained glasses were investigated by studying absorption, photoluminescence and electron paramagnetic resonance properties. The diffusion parameters (diffusion coefficient and diffusion activation energy) of silver ions were calculated based on elemental analysis data from inductively coupled plasma (ICP) spectrometry, and line scan profiles from energy dispersion X-ray analysis (EDX).     

Sol-gel synthesis of erbium-doped yttrium silicate glass-ceramics

Yttrium silicate glasses and glass-ceramics were prepared by the sol-gel process. Yttrium nitrate was added to tetraethyl orthosilicate in amounts representing between 0.2 and 20 mol%, as well as amounts corresponding to the disilicate composition. Some samples were doped with erbium acetate. The solutions underwent gellation in 2-7 days and were dried for 2 weeks. Differential thermal analysis was used to design a multi-step heat treatment to 1000 °C to densify samples to transparent or translucent monoliths. Above 1000 °C, samples crystallized to yttrium disilicate and cristobalite. Phase separation before crystallization influenced the formation of the crystal phases.     

Glass formation in the MoO3-CuO-PbO system

Glasses in the MoO₃-CuO-PbO system are obtained at high cooling rates (10⁴-10⁵ K/s) and characterized using X-ray diffraction (XRD), differential thermal analysis (DTA), infrared (IR) and X-ray photoelectron spectroscopy (XPS). Two glass formation regions are determined: one with compositions having a high MoO₃ content (50-80 mol%) and the other in the PbO-rich compositions (65-80 mol%). In the region of MoO₃-rich compositions the building units of the amorphous network are МоО₆, МоО₄ and CuO₄ groups. For these high MoO₃ contents and respectively low PbO concentrations, the lead oxide is supposed to act as a network modifier while at high content PbO is found to be the main glass network former. In latter case the structure of glasses is formed by chains of PbO_n (n = 3, 4) polyhedra, between which there are isolated MoO₄ and CuO₄ complexes. IR and XPS data reveal the existence of Mo-O-Mo, Mo-O-Me(Me’) (where Me = Cu²⁺, Cu¹⁺ and Me’ = Pb) and Me(Me’)-O-Me(Me’) bonds in the amorphous network. Surprising result is found for low PbO content (10 mol%) where the lead oxide acts as glass network modifier: the actual MoO₃ content drops strongly which is accompanied with a significant increase of the actual CuO content with respect to their nominal MoO₃-CuO composition. Such effect is not observed in PbO-rich composition (70 mol%) where PbO has a role of network former.     

Luminescence of GeO2 glass, rutile-like and α-quartz-like crystals

The luminescence of GeO₂ rutile-like crystals was studied. Crystals were grown from a melt of germanium dioxide and sodium bicarbonate mixture. Luminescence of the crystal was compared with that of sodium germanate glasses produced in reduced and oxidized conditions. A luminescence band at 2.3 eV was observed under N₂ laser (337 nm). At higher excitation photon energies and X-ray excitation an additional band at 3 eV appears in luminescence. The band at 2.3 eV possesses intra-center decay time constant about 100 μs at 290 K and about 200 μs at low temperature. Analogous luminescence was obtained in reduced sodium germanate glasses. No luminescence was observed in oxidized glasses under nitrogen laser, therefore the luminescence of rutile-like crystal and reduced sodium germanate glass was ascribed to oxygen-deficient luminescence center modified by sodium. The band at 2.3 eV could be ascribed to triplet-singlet transition of this center, whereas the band at 3 eV, possessing decay about 0.2 μs, could be ascribed to singlet-singlet transitions. Both bands could be excited in recombination process with decay kinetics determined by traps, when excitation realized by ArF laser or ionizing irradiation with X-ray or electron beam. Another luminescence band at 3.9 eV in GeO₂ rutile-like crystal was obtained under ArF laser in the range 100-15 K. Damaging e-beam irradiation of GeO₂ crystal with α-quartz structure induces similar luminescence band.     

Influence of heat treatment on spectroscopic properties of Er in multicomponent ZrF4-ZnF2-AlF3-YF3-MF2 (M = Ca, Sr, Ba) based glass

Er³⁺ doped multicomponent fluoride based glass was prepared. These precursor fluoride glass samples were then heated using different schedules. Crystalline phase particles were successfully precipitated in the multicomponent fluoride glass samples after heat treatment. The influence of heat treatment on the spectroscopic properties of Er³⁺ in multicomponent fluoride based glass samples were discussed. Small changes of the Judd-Ofelt parameters Ω_i (i = 2, 4, 6) were found in multicomponent fluoride glass samples before and after heat treatment compared to oxyfluoride telluride glass. Preparation conditions used to produce transparent multicomponent fluoride glass ceramics doped with rare-earth ions are discussed.     

Formation of photoelectron holograms of crystals excited by synchrotron radiation

The theoretical aspects of formation of photoelectron beams excited by the ultraviolet synchrotron radiation incident onto a crystal are considered. It is shown that the change in the energy of the monochromatized synchrotron radiation incident onto a hematite crystal results in the change of the number of reflections participating in the hologram formation.     

Optical properties of and concentration quenching in Bi2O3-B2O3-Ga2O3 glasses

Er₂O₃-doped Bi₂O₃-B₂O₃-Ga₂O₃ glasses were prepared by the conventional melt-quenching method, and the Er³⁺:⁴I_13/2 → ⁴I_15/2 fluorescence properties are studied for different Er³⁺ concentrations. when the Er₂O₃ concentration increases from 0.03 to 3.0 mol%, the measured lifetime of Er³⁺:⁴I_13/2 level decrease from 2.24 to 0.9 m s, and from 0.25 to 0.20 m s for the Er³⁺:⁴I_11/2 level. The fast energy migration among Er³⁺ ions cause the reduction of lifetime of the ⁴I_13/2 level, whereas the change in the ⁴I_11/2 level is mainly due to a cooperative upconversion process (⁴I_11/2, ⁴I_11/2) → (⁴F_7/2, ⁴I_15/2). Based on the dipole-dipole interaction theory, the interaction parameter, C_Er,Er, for the migration rate of Er³⁺:⁴I_13/2 ↔ ⁴I_13/2 was calculated to be 32 × 10⁻⁴⁰ cm⁶ s⁻¹.     

Spectroscopic properties of Er-doped Na2O-Sb2O3-B2O3-SiO2 glasses

Spectroscopic properties of Er³⁺-doped Na₂O-Sb₂O₃-B₂O₃-SiO₂ glasses have been investigated for developing 1.5-μm broadband fiber amplifiers. An intense 1.5-μm near infrared emission with a broad full width at half maximum (FWHM) of 88 nm has been obtained for Er³⁺-doped 5Na₂O-20Sb₂O₃-35B₂O₃-40SiO₂ glass upon excitation with a 980 nm laser diode. The obtained emission cross-section of the ⁴I_13/2 → ⁴I_15/2 transition and the lifetime of the ⁴I_13/2 level of Er³⁺ ions are 6.8 × 10⁻²¹ cm² and 0.36 ms, respectively. It is noted that the product of the emission cross-section and the FWHM of the glass, σ_e × FWHM, is as great as 598.4 × 10⁻²¹ cm² nm, which is comparable or higher than that of Er³⁺-doped bismuth-based and tellurite-based glasses. These special optical properties encourage in identifying them as important materials for potential applications in high performance optics and optical communication networks.     

Investigation of infrared emission and lifetime in Tm-doped 75TeO2:20ZnO:5Na2O (mol%) glasses: Effect of Ho and Yb co-doping

In this paper we describe fabrication and characterization of rare-earth-doped active tellurite glasses to be used as active laser media for fiber lasers emitting in the 2 μm region. The base composition is (mol%): 75TeO₂-20ZnO-5Na₂O with different concentrations of Tm³⁺, Yb³⁺ and Ho³⁺ as dopants or co-dopants. Optical properties of doped glasses were studied and pumping at 800 nm and at 980 nm were tested in order to compare the efficiency of two pumping mechanisms. Optical characterization carried out on glasses containing only Tm³⁺ ions indicated the optimum concentration of Tm₂O₃ in terms of emission efficiency as 1 wt%. The addition of 5 wt% of Yb₂O₃ to Tm³⁺-doped glasses led to the best results in terms of intensity of fluorescence emission and of lifetime values. Yb and Ho co-doped Tm-tellurite glass was measured in emission.     

Erbium doped fluoride glass-ceramics waveguides fabricated by PVD

Transparent amorphous and glass-ceramics waveguides in the system ZrF₄-LaF₃-ErF₃-AlF₃ (ZELA) have been fabricated by physical vapor deposition (PVD). The ceramming process was studied by means of X-ray diffraction and transmission electron microscopy for different deposition temperatures. With increasing deposition temperature, formation of La_xEr_1−xF₃ nanocrystals with x ∼ 0.3 was observed. The decay curves of the ⁴I_13/2 level in the glass-ceramics with 14.5 mol% Er³⁺ gave evidence of the presence of erbium both in the amorphous matrix (τ = 8.6 ms) and in the crystal phase (τ = 2.2 ms). The decrease of lifetime was due to clustering of erbium incorporated in LaF₃ crystal lattice. No significant increase of attenuation loss was detected after waveguide cerammization (1.3 dB/cm at 1304 nm).     

Dynamics of excited state relaxation and frequency upconversion in Tm3+ and Tm3+/Tb3+ doped ZBLAN glass

The effects of activator concentration on the relaxation of the ¹I₆, ¹D₂, ¹G₄ and ³H₄ levels of Tm³⁺ were investigated by the analysis of the fluorescence decay curves in Tm³⁺ and Tm³⁺/Tb³⁺ doped ZBLAN glasses. UV and blue upconversion luminescence bands around 362 and 450 nm were observed by 655 nm laser excitation in all the samples. The upconversion mechanism was attributed to excited state absorption (ESA) by analyzing the decay profiles and the intensity dependence.     

Optical properties of Ho-doped alumino-germano-silica glass optical fiber

We present the optical characteristics of Ho-doped alumino-germano-silica glass fiber prepared by the Modified Chemical Vapor Deposition (MCVD) technique. Strong absorption peaks were observed at 1153 nm, 890 nm, 653 nm and 551 nm and another peak around 1726 nm. A possibility of lasing in the Ho-doped alumino-germano-silica glass fiber is shown by the Judd-Ofelt analysis predicting the multiple visible emissions around 550 nm and 650 nm and near infra red emissions around 1050 nm and beyond 1726 nm.     

Studies of Er doped germanate-oxyfluoride and tellurium-germanate-oxyfluoride transparent glass-ceramics

An erbium doped germanate-oxyfluoride glass 60GeO₂ · 20PbO · 10PbF₂ · 10CdF₂ (GPOF) and a tellurium-germanate-oxyfluoride glass 30TeO₂ · 30GeO₂ · 20PbO · 10PbF₂ · 10CdF₂ (TGPOF) were prepared in the bulk form. By appropriate heat treatment of the as-prepared glasses above, transparent glass-ceramics were obtained with the formation of β-PbF₂ nanocrystals in the glass matrix confirmed by X-ray diffraction. Optical absorption and photoluminescence measurements were performed on as-prepared glass and glass-ceramics. The luminescence of Er³⁺ ions in transparent glass-ceramics revealed sub-band splitting generally seen in a crystal host. The intensity of red and near infrared luminescence significantly increased in transparent glass-ceramic compared to that in as-prepared glass. Two luminescence bands at 758 nm from ⁴F_7/2 → ⁴I_13/2 and at 817 nm from ²H_11/2 → ⁴I_13/2 transitions were observed from transparent glass-ceramic but cannot be seen from the corresponding as-prepared glass. These results are attributed to the change of ligand field of Er³⁺ ions and the decrease of effective phonon energy when Er³⁺ ions were incorporated into the precipitated β-PbF₂ nanocrystals.     

Double implantation in silica glass for metal cluster composite formation: a study by synchrotron radiation techniques

Silica glass containing metal clusters is studied for both basic and applied aspects, related to the physics of cluster formation and to the optical properties of these materials. To obtain such composite structure, Cu + Ni, Au + Cu, Au + Ag, Cu + Co, and Cu + Ag sequential implantations in fused silica were realized. The resulting systems, after possible annealing in various atmospheres, were studied by synchrotron radiation-based techniques, namely, extended X-ray absorption fine structure (EXAFS) spectroscopy, grazing incidence X-ray diffraction (GIXRD), and grazing incidence small angle X-ray scattering (GISAXS). The unique potential of these techniques is the capability to investigate dilute (volume fraction of clusters0.01) and very thin (50 nm) systems. In the presented experiment, both pure and alloy clusters in the nanometer range of size were observed to form, pointing out the complexity of the cluster formation process in terms of physical and chemical driving forces.     

X-ray diffraction measurement of liquid As2Se3 by using third-generation synchrotron radiation

X-ray diffraction (XD) measurements of liquid As₂Se₃ were carried out in the temperature range up to 1600 °C where the temperature is well beyond the semiconductor to metal (SC–M) transition temperature around 1000 °C. The measurements were done by using third-generation synchrotron radiation at SPring-8 and the obtained structure factors have been much improved compared to previous in house XD measurements with regard to the momentum transfer range and the data statistics. The deduced pair distribution functions show that with increasing temperature, the position of the first peak does not change within the errorbar and the coordination number gradually decreases up to 1600 °C irrespective of the SC–M transition. These results coincide with those of the first-principle molecular dynamics simulation.     

Maskless selective growth of semi-polar (1 12¯ 2) GaN on Si (3 1 1) substrate by metal organic vapor phase epitaxy

Semi-polar (1 1 2¯ 2) GaN layers were selectively grown by metal organic chemical vapor phase epitaxy on patterned Si (3 1 1) substrates without SiO₂ amorphous mask. The (1 1 2¯ 2) GaN layers could be selectively grown only on Si (1 1 1) facets when the stripe mask width was narrower than 1 μm even without SiO₂. Inhomogeneous spatial distribution of donor bound exciton (DBE) peak in low-temperature cathodoluminescence (CL) spectra was explained by the difference of growth mode before and after the coalescence of stripes. It was found that the emission intensity related crystal defects is drastically decreased in case of selective growth without SiO₂ masks as compared to that obtained with SiO₂ masks.     

One-sidewall-seeded epitaxial lateral overgrowth of a-plane GaN by metalorganic vapor-phase epitaxy

The selective regrowth of GaN during sidewall-seeded epitaxial lateral overgrowth was performed. In addition to adjusting the V/III ratio, control of offset angle of the sidewall was found to be effective for realizing one-sidewall-seeded a-plane (1 1 2¯ 0) GaN on r-plane (1 1¯ 0 2) sapphire. The number of coalescence regions on the grooves was reduced, and threading-dislocation and stacking-fault densities as low as 10⁶–10⁷ cm⁻² and 10³–10⁴ cm⁻¹, respectively, were successfully realized.     

Numerical simulation of experimental resonance absorption spectra and diffraction of synchrotron radiation in yttrium iron garnet

Extended X-ray absorption fine-structure spectra of yttrium-iron garnet, measured near the absorption edges of iron and yttrium at the Kurchatov synchrotron radiation source are reported. Numerical simulation of the X-ray absorption near-edge structure of these spectra is performed and good agreement with the experimental data is obtained. It is shown theoretically that “forbidden” Bragg reflections can be observed near the absorption edges of iron and yttrium. The indices of these reflections are determined. The energy structure of the “forbidden” reflections 006 and 110 is calculated.     

Spectroscopic properties of Er-Yb co-doped glass ceramics containing BaF2 nanocrystals

A Er³⁺ and Yb³⁺ co-doped transparent oxyfluoride glass ceramic containing BaF₂ nanocrystals has been prepared. The formation of BaF₂ nanocrystals in the glass ceramic was confirmed by X-ray diffraction. Intense upconversion luminescence in the Er³⁺ and Yb³⁺ co-doped glass ceramic could be observed. Stark splitting of the Er³⁺ upconversion luminescence peaks in the glass ceramic indicated that Er³⁺ and Yb³⁺ had been incorporated into the BaF₂ nanocrystals. Near infrared luminescence decay curves showed that the Er³⁺ and Yb³⁺ co-doped glass ceramic had higher luminescence efficiency than the precursor glass.