Ge and Ga K-edge EXAFS analyses on the structure of Ge-Ga-S-CsBr glasses

The local structure of Ge and Ga ions in (1 − x)(Ge_0.25Ga_0.10S_0.65)-xCsBr glasses (x = 0.00, 0.05, 0.10 and 0.12) were investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy. CsBr formed [GaS_3/2Br]⁻ structural units in glass while Ge ions remained in GeS_4/2 tetrahedra, unaffected by CsBr addition. Rare-earth ions can be surrounded by Br ions only when CsBr/Ga ratio in glass became larger than unity.     

Emission and local structure of rare-earth ions in chalcogenide glasses

Local structures of rare-earth ions in Ge–Ga–S–CsBr glasses were investigated to understand the structural origin on the emission property enhancement. The frequency of the phonon vibration controlling the multiphonon relaxation was changed to 245 cm⁻¹ due to the formation of Ga–Br bonds with CsBr addition to sulfide glasses. Formation of this new chemical bond was also confirmed from the phonon side band spectra of Eu³⁺ ions. Analyses of the EXASF spectra proved that Tm³⁺ ions were surrounded by approximately seven S ions in Ge_0.25Ga_0.10S_0.65 glass but were coordinated by ∼6 Br ions in the glass with 10 mol% of CsBr.     

Emission properties and local structure of Tm3+ in Ge–Ga–S–Br glass

Spectroscopic properties of Tm³⁺ in (1 − x) (Ge_0.25Ga_0.10S_0.65)–xBr (or CsBr) glasses (x = 0.0 and 0.1) were investigated. Emission properties of Tm³⁺ in 0.9(Ge_0.25Ga_0.10S_0.65)–0.1Br glass were similar to those in Ge_0.25Ga_0.10S_0.65 glass, while there was significant improvement when doped into 0.9(Ge_0.25Ga_0.10S_0.65)–0.1CsBr glass. The lifetime of the Tm³⁺:³H₄ level increased from 0.23 to 1.22 msec with 10 mol% CsBr addition. The presence of Cs⁺ facilitated the formation of [GaS_3/2Br]⁻ units by donating an electron to the Ga tetrahedron, resulting in the homogeneous distribution of Br. In this way, Tm³⁺ ions have their local environment made of Br only. When Br ions were added instead of CsBr, [GaS_(4−x)/2Br]⁻ units with x > 1 were formed and Tm³⁺ ions were surrounded by both S and Br, producing a high phonon environment.     

EXAFS investigation on the structural environment of Tm3+ in Ge–Ga–S–CsBr glasses

The local structures around Tm³⁺ in Ge_0.25Ga_0.10S_0.65 and 0.90 (Ge_0.25Ga_0.10S_0.65) − 0.10CsBr glasses were investigated using Extended X-ray absorption fine structure (EXAFS) spectroscopy. In Ge_0.25Ga_0.10S_0.65 glass, Tm³⁺ ions are surrounded by approximately seven S ions. Addition of 10 mol% CsBr resulted in significant changes in the EXAFS spectrum of Tm³⁺ ions due to the changes in the local structure surrounding Tm³⁺ ions. The first-nearest coordination shell around Tm³⁺ ion is predominantly composed of about six Br ions in 0.90 (Ge_0.25Ga_0.10S_0.65) − 0.10CsBr glass.     

Structural and optical properties in gadolinium-aluminum-lead-germanate quaternary glasses

Glasses in the quaternary system 0.05Al₂O₃·0.95[xGd₂O₃·(100-x)(7GeO₂·3PbO)] with 0 ≤ x ≤ 40 mol% have been prepared from melt quenching method. In this paper, we investigated structural and optical properties in gadolinium-alumino-lead-germanate glasses through investigations of FTIR (Fourier-Transform Infrared Spectroscopy) and UV-VIS (Ultra-Violet) spectroscopy.The observations presented in these mechanisms show that by increasing Gd₂O₃ content up to 40 mol%, the glass network modification has taken place mainly in the germanate part, while the excess of oxygen can be accommodated in the host network by the creation of shorter rings of [Ge₂O₇] structural units and the formation of [AlO₄] structural units. The affinity pronounced of the gadolinium cations towards germanate structural units produces the formation of the Gd₂Ge₂O₇ crystalline phase.The UV-VIS spectroscopy data show the charge transfer transitions of Pb^+ 2-O^− 2, Al^+ 3-O^− 2 and Gd^+ 3-O^− 2, respectively. The additional absorption in the range of 300 to 600 nm was attributed to other types of defects such as: non-bridging oxygen ions, change in valency of ions and other color centers.The values of the direct optical band gap of the glasses are determined from the optical absorption spectra. By increasing Gd₂O₃ content in the glass matrix, the optical band gap energy increases indicating changes of the lattice parameters by Gd₂O₃ incorporation.     

Study of optical and conducting properties of FeCl3 doped PVA polymers

In the present work, PVA and various concentrations of FeCl₃ doped PVA polymer were prepared and optical studies like IR and UV/Visible analysis were carried out on them in solution form also the cast films were examined for their conductance. The variation of optical band gap of PVA polymer with the addition of Fe³⁺ transition metal ion has been determined by the Tauc plot method. It is found that the optical band gap and the transmittance of the polymer solutions being decreased with the increase in the concentration of Fe³⁺ ion, and thus obeys Beer's Law. This is supported by conductivity obtained for these polymers and FT-IR spectra which shows the stretching of the various bonds of the polymer due to the addition of transition metal (Fe³⁺) ions.     

Compositional dependences on the mechanism of upconversion in Nd3+/Tm3+ co-doped chalcohalide glasses

Mechanisms of the compositional dependence of blue emission from Nd³⁺/Tm³⁺ co-doped Ge–Ga–S–CsBr chalcohalide glasses were investigated. The blue upconversion emissions (centered at 475 nm) due to the Tm³⁺: ¹G₄ → ³H₆ transition decreased as the CsBr/Ga ratio in glasses while the other upconversion emissions from the Nd³⁺ ions increased. Changes in the local environment of rare-earth ions incurred by the CsBr addition significantly increased the excited state absorption within Nd³⁺ ions. This resulted in the decrease in the Nd³⁺ → Tm³⁺ energy transfer rates that led to the large decrease in blue upconversion emission.     

Growth and luminescence of CsBr:Cu crystals

Special features of the incorporation of a copper impurity into CsBr crystals are studied for different types of impurities (metallic copper, CuO, and CuBr₂) and crystal-growth techniques (the Bridgman method or the method of isothermal evaporation from solution). The optical characteristics of these crystals (absorption, photoluminescence, and photostimulated-luminescence spectra) are investigated. The copper impurity is shown to enter CsBr:Cu_met crystals in the monovalent state Cu⁺ and CsBr:CuO and CsBr:CuBr₂ crystals in the divalent state Cu²⁺. It is found that the CsBr crystals doped with Cu⁺ and Cu²⁺ ions exhibit intense photostimulated luminescence and can be used as storage phosphors for visualization of X-ray images.     

The effect of oxygen partial pressure on physical properties of nano‐crystalline silver oxide thin films deposited by RF magnetron sputtering

Nano‐crystalline silver oxide films were deposited on glass and silicon substrates held at room temperature by RF magnetron sputtering of silver target under different oxygen partial pressures. The influence of oxygen partial pressure on the structural, morphological, electrical and optical properties of deposited films was investigated. Varying oxygen partial pressure during the sputter deposition leads to changes of mixed phase of Ag₂O and Ag to a single phase of Ag₂O and to AgO. The X‐ray diffraction and X‐ray photoelectron spectroscopy results showed the formation of single phase Ag₂O with cubic structure at oxygen partial pressures of 2x10^‐2 Pa while the films deposited at higher oxygen partial pressure of 9x10^‐2 Pa showed the formation of single phase of AgO with monoclinic structure. Raman spectroscopic studies on the single phase Ag₂O showed the stretching vibration of Ag‐O bonds. Single‐phase Ag₂O films obtained at oxygen partial pressure of 2x10^‐2 Pa were nano‐crystalline with crystallite size of 20 nm and possessed an electrical resistivity of 5.2x10^‐3 Ωcm and optical band gap of 2.05 eV. The films deposited at higher oxygen partial pressure of 9x10^‐2 Pa were of AgO with electrical resistivity of 1.8x10^‐2 Ωcm and optical band gap of 2.13 eV. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Correlation between physical and structural properties of Co doped mixed alkali zinc borate glasses

The physical and structural properties of Co²⁺ doped 20ZnO + xLi₂O + (30 − x)Na₂O + 50B₂O₃ (5 ≤ × ≤ 25) (ZLNB) glasses have been studied and correlated. The physical and structural parameters of all the glasses are evaluated and a non-linear behavior is observed. No sharp peaks are observed in XRD patterns of the glass samples which confirm the amorphous nature. FT-IR spectra of ZLNB glasses reveal diborate units in borate network. The optical absorption spectra suggest the site symmetry of Co²⁺ in the glasses is near octahedral. Crystal field and inter-electronic repulsion parameters are also evaluated. The optical band gap and Urbach energies exhibit the mixed alkali effect. All the samples are found to be strong and stable in structure with low values of Urbach energy which lie between 0.027 eV and 0.039 eV. The correlation between densities and Urbach energies of Co²⁺ doped ZLNB glasses with respect to Li₂O content suggest a changeover conduction mechanism from electronic to ionic, with a diffusivity crossover point at x = 15 mol%.     

Properties of Sm‐doped CaNb2O6 thin films deposited by radio‐frequency magnetron sputtering

Sm‐doped CaNb₂O₆ (CaNb₂O₆:Sm) phosphor thin films were prepared by radio‐frequency magnetron sputtering on sapphire substrates. The thin films were grown at several growth temperatures and subsequently annealed at 800 °C in air. The crystallinity, surface morphology, optical transmittance, and photoluminescence of the thin films were investigated by X‐ray diffraction, scanning electron microscopy, ultraviolet‐visible spectrophotometry, and fluorescence spectrophotometry, respectively. All of the thin films showed a main red emission radiated by the transition from the ⁴G_5/2 excited state to the ⁶H_9/2 ground state of the Sm³⁺ ions and several weak bands under ultraviolet excitation with a 279 nm wavelength. The optimum growth temperature for depositing the high‐quality CaNb₂O₆:Sm thin films, which was determined from the luminescence intensity, was found to be 400 °C, where the thin film exhibited an orthorhombic structure with a thickness of 370 nm, an average grain size of 220 nm, a band gap energy of 3.99 eV, and an average optical transmittance of 85.9%. These results indicate that the growth temperature plays an important role in controlling the emission intensity and optical band gap energy of CaNb₂O₆:Sm thin films.     

Structural and optical properties of the gadolinium-lead-germanate glasses

Glasses in the system xGd₂O₃(100 − x)[7GeO₂·3PbO] with 0 ≤ x ≤ 40 mol% have been prepared from melt quenching method. The influence of gadolinium ions on structural behavior in lead-germanate glasses has been investigated using FTIR, UV-VIS and EPR spectroscopy. The structural changes have been analyzed with increasing rare earth concentration.FTIR data suggest that the glass network modifications has taken place mainly in the germanate part whereas the lead part remained unmodified and its network consists mainly from the [GeO₄], [GeO₆], [Ge₂O₇] structural units and with interconnected through Ge-O-Ge bridges in [GeO₄] structural units. The changes in amplitude and bandwidth of the UV-VIS bands ranging from 200 nm to 350 nm depend on the content of Gd₂O₃.By increasing the Gd₂O₃ content in the glass matrix, the optical band gap energy increases, indicating changes of the lattice parameters and that no non-bridging-oxygens form upon the addition of gadolinium oxide. The decreasing trend has been observed both in optical gap band energy and refractive index of oxide glasses at x = 10 mol% Gd₂O₃ indicating breaks up the [GeO₄] tetrahedral units bonds and create of non-bridging oxygen atoms. For sample with x ≥ 20 mol%, the gadolinium ions having a behavior of network formers (g ≈ 4.8) will coordinate more with the excess of oxygen. Accordingly, the gadolinium ions are generally suspected to improve their environment of network formers.     

Local and medium range structure of erbium containing glasses: A molecular dynamics study

Erbium containing glasses cover an important role in optical communications and laser technology. The local environment of the ions constituting the three dimensional network exerts a strong influence on the chemical and physical properties of the glasses. In particular the network modifier cations strongly influence the short and intermediate range order of the glass structure. The structural modifications induced by the alumina addition in the glass matrix, as a function of the erbium oxide concentration, have been studied using molecular dynamics (MD) simulations. While at low Er₂O₃ concentration the network former action of the Al³⁺ leads to a more polymerized glass network, at higher Er₂O₃ content the influence of the alumina on the erbium local structure is limited. Further investigation points out micro-heterogeneity in the Na⁺ and Ca²⁺ distribution as a function of the alumina concentration.     

Temperature Dependence of the Absorption Spectra and Optical Parameters in TGS and Cu2+-Doped TGS Crystals

The effect of temperature on the optical absorption spectra and optical parameters is investigated for pure TGS and TGS doped with Cu²⁺ ions. Absorption measurements cover the range from room temperature to about 355 K in the energy range 3-5.5 eV. The temperature dependence of the band gap E_g(T) reveals an anomaly at the phase transition temperature for both pure and Cu²⁺-doped TGS crystals. In the region of the absorption edge the absorption coefficient is found to display Urbach-rule behaviour. The characteristic Urbach parameters are determined and their temperature dependence is investigated.     

Compositional effects on fluorescence lifetime of Dy3+ ions embedded in chalcogenide Ge–As–S glasses containing very small amount of Ga and CsBr

We have investigated the fluorescence lifetimes of Dy³⁺: 1.3 μm emission in the chalcogenide Ge–As–S glasses with different compositions but identically containing 0.5 mol% Ga and 0.5 mol% CsBr. The measured lifetimes turn out to be sensitive not only to the concentrations of Ga and CsBr but also to compositional variations in the Ge–As–S host glasses. The lifetime is enhanced conspicuously in glass of the S-sufficient compositions, relative to the stoichiometric GeS₂–As₂S₃ composition, while this effect is not significant in the S-exact and S-deficient compositions. We employ Ga K-edge EXAFS analysis to support that the local structural environments of Ga in the modified chalcogenide glasses are closely correlated with the lifetime enhancement effect.     

1.48 μm emission properties and the cross-relaxation mechanism in chalcohalide glass doped with Tm

1.48 μm emission properties and the cross-relaxation mechanism of Tm³⁺ ions in 0.7(Ge_0.25As_0.10S_0.65) + 0.15GaS_3/2 + 0.15CsBr glass were investigated. Both the relative intensity ratio of the 1.48 μm emission to 1.82 μm and the measured lifetime of the ³H₄ level decreased with increasing Tm³⁺ concentration. When temperature decreased from room temperature to 20 K, lifetimes of the ³H₄ level increased from 670 to 970 μs. At the same time, the critical distance for cross-relaxation decreased from 1.11 to 0.93 nm. These results indicate that cross-relaxation (³H₄, ³H₆ → ³F₄, ³F₄) became less effective as temperature decreased. Analysis of the temperature dependence of cross-relaxation rates showed that cross-relaxation in Tm³⁺ is a phonon-assisted energy transfer process. The major phonon contributing to the process is from the Ga-Br vibration in [GaS_3/2Br]⁻ units.     

Effects of annealing on structural,electrical and optical properties of AgGa(Se0.5S0.5)2 thin films deposited by using sintered stoichometric powder

The structural, electrical and optical properties of AgGa(Se_0.5S_0.5 )₂ thin films deposited by using the thermal evaporation method have been investigated as a function of annealing in the temperature range of 450–600 °C. X‐ray diffraction (XRD) analysis showed that the structural transformation from amorphous to polycrystalline structure started at 450 ^oC with mixed binary phases of Ga₂Se₃, Ga₂S₃, ternary phase of AgGaS₂ and single phase of S. The compositional analysis with the energy dispersive X‐ray analysis (EDXA) revealed that the as‐grown film has different elemental composition with the percentage values of Ag, Ga, Se and S being 5.58, 27.76, 13.84 and 52.82 % than the evaporation source powder, and the detailed information about the stoichometry and the segregation mechanisms of the constituent elements in the structure have been obtained. The optical band gap values as a function of annealing temperature were calculated as 2.68, 2.85, 2.82, 2.83, and 2.81 eV for as‐grown, annealed at 450, 500, 550, and 600 °C samples, respectively. It was determined that these changes in the band gap are related with the structural changes with annealing. The temperature dependent conductivity measurements were carried out in the temperature range of 250‐430 K for all samples. The room temperature resistivity value of as‐grown film was found to be 0.7x10⁸ (Ω‐cm) and reduced to 0.9x10⁷ (Ω‐cm) following to the annealing. From the variation of electrical conductivity as a function of the ambient temperature, the activation energies at specific temperature intervals for each sample were evaluated. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

Degradation of nickel (86 MeV) ion irradiated polystyrene

Samples of polystyrene films were irradiated under vacuum at room temperature with ⁵⁸Ni⁷⁺ (86 MeV) ion with fluences ranging from 1 × 10¹¹ to 1 × 10¹³ ions cm⁻². Ion induced structural modifications were studied by means of atomic force microscopy atomic force microscopy (AFM), X-ray diffraction (XRD), UV-visible absorption spectroscopy (UV-Vis) and Fourier transform infrared spectroscopy (FTIR) techniques. Atomic force microscopy shows that the root mean square (RMS) roughness of the irradiated polystyrene surface increases with the increment of ion fluence. XRD analysis reveals that in addition to the increase of amorphization of polymer with the increase of ion fluence there is also an increase of ordering (to a small extent) in some of the micro-domains. These results have further been supported by the study of optical and chemical analysis. The analysis of present study shows that the increase of full width at half maximum (FWHM) of first peak of XRD spectra, decrease of optical band gap and the formation of new alkyne group may be attributed to the increase of amorphization of polystyrene. Similarly, sharpening of second X-ray diffraction peak, decrease of Urbach’s energy and increase in the absorbance ratio of I₁₂₂₂/I₁₁₈₃ may be owed to the increase of ordering in some domains.     

Influence of Y2O3 on structural and optical properties of SiO2-BaO-ZnO-xB2O3-(10−x) Y2O3 glasses and glass ceramics

SiO₂-BaO-ZnO-xB₂O₃-(10−x) Y₂O₃, (0 ≤ x ≤ 10) glasses are synthesized. The effect of Y₂O₃ on the structural and optical properties of glasses has been investigated using different characterization techniques. The results are discussed in light of non-bridging oxygens (NBO), optical basicity and heat-treatment of glasses. The band gap has been calculated for as cast and heat-treated glasses. The band gap energy is found to decrease with the increasing content of Y₂O₃ in the glasses and heat-treatment. The presence of the crystalline phase in the glass matrix showed remarkable effect on band gap which decreases to semiconducting range.