Compositional trends in low-temperature photoluminescence of heavily Er-doped GeS2–Ga2S3 glasses

The influence of temperature and glass composition on the photoluminescence (PL) efficiency of Er³⁺ ions embedded in (GeS₂)_100?x(Ga₂S₃)_x (x = 20, 25 and 33 mol%) glasses has been studied. The typical 4f–4f emission bands of Er³⁺ ions at around 830, 1000 and 1550 nm have been observed in the whole investigated temperature range from 300 K down to 10 K for all the compositions. New 4f–4f luminescence bands, in excess of the three basic ones, have been observed at 670, 870, 1120, 1260 and 1350 nm for (GeS₂)₇₅(Ga₂S₃)₂₅ glass composition, and are tentatively assigned to ²H_9/2 → ⁴I_11/2, ⁴G_11/2 → ⁴F_9/2, ²H_11/2 → ⁴I_11/2, ⁴F_7/2 → ⁴I_9/2 and ⁴F_3/2 → ⁴I_9/2 transitions, respectively. Thus a considerable influence of GeGaS host composition on the efficiency of 4f–4f transitions of embedded Er³⁺ ions is documented with the outcome that (GeS₂)₇₅Ga₂S₃)₂₅ composition appears near optimal for the emission efficiency of Er³⁺ ions. With decreasing temperature the PL efficiency is enhanced considerably with pronounced narrowing of all bands. In the case of the strongest PL band at ~ 1550 nm, corresponding to ⁴I_13/2 → ⁴I_15/2 transition, the narrowing at low temperature is further accompanied by the resolution of well pronounced fine structure due to “crystal field” splitting of corresponding electronic terms. The relationship between the photoluminescence and reflectance spectra as a function of Er content has been discussed.     

New chalcohalide glasses from the GeS2–In2S3–CsCl system

New chalcohalide glasses from GeS₂–In₂S₃–CsCl pseudo-ternary system were prepared using the conventional melt-quenching method and its glass-forming region has been determined. The differences ΔT (T_P ? T_g) of partial glasses are large enough (>100 K) to permit the preparation of performs of considerable size. With the increased content of CsCl, the visible absorption edge (λ_vis) of these glasses indicates a distinct blue shift while a clear drop of their glass transition temperatures can be seen. The ultrafast non-linearity of partial glasses was measured using the Kerr shutter technique. The non-linear refractive index, n₂, was estimated to be in the magnitude of 10^?14 cm²/W. Widely transparent range, good glass-forming ability, higher χ⁽³⁾ and large electronic ultrafast OKE response make these glasses the potential applications in current photonic fields.     

Ion conductive chalcohalide glasses in LiI–Ga2S3–GeS2 system

The electric properties of LiI containing chalcohalide glasses in the system Ga₂S₃–GeS₂ were studied by means of impedance spectroscopy and potentiostatic chronoamperometry. Two sets of the samples were prepared by direct synthesis from elements and compounds in evacuated quartz ampoules. The prepared glasses were as follows: xLiI–xGa₂S₃–(100?2x)GeS₂, x = 15, 20, 25 and 20LiI–xGa₂S₃–(80?x)GeS₂, x = 0, 5, 10, 15 and 20. In the first set the concentration of LiI increased and the second set was prepared to study the influence of Ga₂S₃ on the properties of the glasses. Additional aim of this work was to compare the electric properties of LiI containing Ga₂S₃–GeS₂ glasses with analogous AgI containing Ga₂S₃–GeS₂ glasses recently studied by us. The conductivity of the LiI containing glasses in the Ga₂S₃–GeS₂ system was higher and the activation energy was lower than in the analogous AgI containing system. The residual electronic (hole) conductivity remained similar in both systems being almost negligibly low. Raman spectroscopy proved the influence of LiI as well as Ga₂S₃ on glass structure, however interpretation of Raman spectra of these glasses is complicated due to small mass difference between gallium and germanium.     

Preparation and third-order optical nonlinearity of glass ceramics based on GeS2–Ga2S3–CsCl pseudo-ternary system

Chalcohalide glass-ceramics based on GeS₂–Ga₂S₃–CsCl pseudo-ternary system were prepared by heat treatment method. X-ray diffraction and scanning electron microscope studies confirmed the formations of Ga₂S₃ and GeS₂ phase grains with sizes of 2–5 and 80 nm, respectively. Z-scan technology was employed to investigate the third-order nonlinear optical characteristics of both precursor glass and its glass ceramics at 800 nm. The results show that nonlinear refractive index n₂ as well as nonlinear absorption coefficient β increase after heat treatment, which is due to quantum effects, and the largest n₂ of the glass ceramics is 4.3 × 10^? 11 esu which is 4 times larger than that of the host.     

Third-order nonlinearity in Ag-nanoparticles embedded 56GeS2–24Ga2S3–20KBr chalcohalide glasses

Ag-nanoparticles were embedded in the 56GeS₂–24Ga₂S₃–20KBr chalcohalide glasses with varied doses by ion implantation. Ag-nanoparticles were observed in the AFM images of all implanted samples. The third-order optical nonlinearity of Ag-implanted chalcohalide glasses was investigated by the femtosecond Z-scan measurements. The results indicated an enhancement of third-order optical nonlinearity due to the formation of Ag-nanoparticles in glasses. The relation between implanting dose and third-order optical nonlinearity was strongly related to the intrinsic local field and interaction of Ag-nanoparticles.     

Synthesis and photoluminescence of Eu3+-doped ZnO–Ga2O3–SiO2 nano-glass-ceramics

Transparent rare-earth Eu³⁺-doped ZnO–Ga₂O₃–SiO₂ nano-glass-ceramics were obtained by a sol–gel method. X-ray diffraction and transmission electron microscopy were used to characterize the as-synthesized materials. Results showed that ZnGa₂O₄ nanocrystals with the size of 5 nm were precipitated from ZnO–Ga₂O₃–SiO₂ system and dispersed in the SiO₂-based glass when the heat-treatment temperature was up to 800 °C. Photoluminescence characterization of Eu³⁺-doped ZnO–Ga₂O₃–SiO₂ nano-glass-ceramics was carried out and the results show that the as-synthesized material display intense emission at 615 nm belonging to ⁵D₀ → ⁷F₂ transition.     

Preparation and properties of chalcogenide glasses in the GeS2–Sb2S3–CdS system

In searching for new kind of photoelectric material, chalcogenide glasses in the GeS₂–Sb₂S₃–CdS system have been studied and their glass-forming region was determined. The system has a relatively large glass-forming region that is mainly situated along the GeS₂–Sb₂S₃ binary side. Thermal, optical and mechanical properties of the glasses were reported and the effects of compositional change on their properties are discussed. These novel chalcogenide glasses have relatively high glass transition temperatures (T_g ranges from 566 to 583 K), good thermal stabilities (the maximum of deference between the onset crystallization temperature, T_c, and T_g is 105 K), broad transmission region (0.57–12 μm) and large densities (d ranges from 2.99 to 3.34 g cm^?3). These glasses would be expected to be used in the field of rare earth doped fiber amplifiers and nonlinear optical devices.     

Spectroscopic properties of Tm3+ doped TeO2-R2O-La2O3 glasses for 1.47 μm optical amplifiers

Upon excitation at 808 nm laser diode, an intense 1.47 μm infrared fluorescence has been observed with a broad full width at half maximum (FWHM) of about 124 nm for the Tm³⁺-doped TeO₂-K₂O-La₂O₃ glass. The Judd–Ofelt parameters found for this glass are: Ω₂ = 5.26 × 10^?20 cm², Ω₄ = 1.57 × 10^?20 cm² and Ω₆ = 1.44 × 10^?20 cm². The calculated emission cross-sections of the 1.47 μm transition are 3.57 × 10^?21 cm², respectively. It is noted that the gain bandwidth, σ_e × FWHM, of the glass is about 440 × 10^?28 cm³, which is significantly higher than that in ZBLAN and Gallate glasses, a high gain of 35.5 dB at 1470 nm can be obtained in a TKL glass fiber. TeO₂-R₂O (R = Li, Na, K)-La₂O₃ glasses has been considered to be more useful as a host for broadband optical fiber amplifier.     

Optical spectroscopy and local structure of Er3+ luminescence centres in СaO–Ga2O3–GeO2 glasses

Optical absorption, luminescence excitation and emission spectra of Er³⁺ centres in Ca₃Ga₂Ge₃O₁₂:Er glass with Er content of 1.46 wt% are presented and analysed. Luminescence kinetics for the main Er³⁺ transitions was satisfactorily described by single exponential decays with characteristic lifetimes. Oscillator strengths, phenomenological Judd–Ofelt intensity parameters, radiative decay rates (emission probabilities of transitions), branching ratios and radiative lifetimes for Er³⁺ centres in Ca₃Ga₂Ge₃O₁₂:Er glass are calculated and compared with the corresponding parameters of the Ca₃Sc₂Ge₃O₁₂:Er³⁺ garnet and other crystals and glasses. Quantum efficiency, η, of the ⁴I_13/2 → ⁴I_15/2 Er³⁺ transition is determined. Incorporation peculiarities and local structure of Er³⁺ luminescence centres in Ca₃Ga₂Ge₃O₁₂:Er³⁺ glass are discussed in comparison with garnet crystals and oxide glasses. On the basis of the presented results and referenced EXAFS data for Er, Eu and Ho impurities (L₃-edge) it has been shown that Er³⁺ centres in Ca₃Ga₂Ge₃O₁₂ glass occupy network sites with the coordination number to oxygen of N = 6.     

Effect of the ytterbium concentration on the upconversion luminescence of Yb3+/Er3+ co-doped PbO–GeO2–Ga2O3 glasses

The effect of Yb³⁺ concentration on the frequency upconversion (UPC) of Er³⁺ in PbO–GeO₂–Ga₂O₃ glasses is reported for the first time. Samples were prepared with 0.5 wt% of Er₂O₃ and different concentrations of Yb₂O₃ (1.0–5.0 wt%). The green (523 and 545 nm) and red (657 nm) emissions are observed under 980 nm diode laser excitation. The dependence of the frequency UPC emission intensity upon the excitation power was examined and the UPC mechanisms are discussed. An interesting characteristic of these glasses is the increase of the ratio of red to green emission, through an increase of the Yb³⁺ concentration due to an efficient energy transfer from Yb³⁺ to Er³⁺.     

Microstructure and thermal properties of the GeS2–In2S3–CsI glassy system

A new series of chalcohalide glasses in the GeS₂–In₂S₃–CsI pseudo-ternary system were prepared by conventional melt-quenching method. The glass-forming region was determined and it is mainly situated in the GeS₂-rich domain. The glasses have relatively high glass transition temperatures (T_g ranges from 335 to 405 °C) and good thermal stabilities. Based on the Raman spectra, it can be speculated that the glassy net is mainly constituted by [GeS₄] and [InS_4?xI_x] tetrahedra, which are interconnected by the bridging sulfur atoms. And the ethane-liked structural units [S₃Ge–GeS₃] can be formed because of the lacking of sulfur. Cs⁺ ion, which was added from CsI, exists as the nearest neighbor of I^? ion.     

Structural dependence of ultrafast third-order optical nonlinearity of Ge–Ga–Ag–S chalcogenide glasses

Ultrafast third-order optical nonlinearity of Ge–Ga–Ag–S chalcogenide glasses at the wavelength of 820 nm has been measured using femtosecond time-resolved optical Kerr (OKE) technique. The results show that Ge–Ga–Ag–S glasses have large third-order optical nonlinear susceptibility, χ⁽³⁾ and the response time is also subpicosecond, which are predominantly due to the ultrafast distortion of electron cloud surrounding the balanced positions of Ge, Ga, Ag and S atoms. What’s more, a strong dependence of χ⁽³⁾ on the composition and microstructure of these glasses was found which shows that [GeS₄] and [GaS₄] tetrahedra play an important role on the third-order optical nonlinearity. These Ge–Ga–Ag–S chalcogenide glasses would be expected as promising materials applied on all-optical switching devices.     

Electronic states of SnO-ZnO–P2O5 glasses and photoluminescence properties

SnO–ZnO–P₂O₅ glasses with 30 and 40 mol% P₂O₅ were prepared by a melting process in an air atmosphere. The glass transition temperature, refractive index, and photoluminescence of the glasses were investigated. The electronic states of Sn(II) and Sn(IV) were determined by Mössbauer spectroscopy. The PO₄ units were investigated by Raman spectroscopy. The glass transition temperature was lower than 450 °C, and decreased as the Sn concentrations increased, so that the minimum was about 250 °C. The refractive index increased as the Sn concentration increased. The emission spectra of the glasses peaked at around 2.0–3.0 eV and depended on the glass compositions.     

Spectroscopic properties of the 1.8 μm emission of Tm3+/Yb3+ codoped TeO2–ZnO–Bi2O3 glasses with efficient energy transfer

Tm³⁺-doped and Tm³⁺/Yb³⁺-codoped TeO₂–ZnO–Bi₂O₃ (TZB) glasses are prepared by melt-quenching method. The Judd-Ofelt intensity parameters (Ω_t t = 2, 4, 6), radiative transition rate, and radiative lifetime of Tm³⁺ are calculated based on the absorption spectra. The 1.8 μm emission of the samples is investigated under 980 nm laser excitation. The absorption, emission cross-sections, and gain coefficient of Tm³⁺:³F₄ → ³H₆ are calculated. The energy transfer processes of Yb³⁺–Yb³⁺ and Yb³⁺–Tm³⁺ are analyzed, the results show that the Yb³⁺ ions can transfer their energy to Tm³⁺ ions with large energy transfer coefficient, and a maximum efficiency of 79%.     

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.     

Structural analysis of xCsCl(1 − x)Ga2S3 glasses

Sulphide glasses doped with rare-earth ions have been demonstrated to be suitable for photonic applications such as optical amplifiers, up-converters and fiber lasers. The substitution of metal halides into the glass network has been shown to result glasses with desirable properties in terms of quantum efficiency and fiber manufacture [J.R. Hector, J. Wang, D. Brady, M. Kluth, D.W. Hewak, W.S. Brocklesby, D.N. Payne, Journal of Non-Crystalline Solids 239 (1998) 176]. To assist in the understanding of this improvement a structural analysis of glasses with a composition xCsCl(1 ? x)Ga₂S₃ has been undertaken in order to examine the nature of the gallium environment. Information collected by high energy X-ray diffraction and neutron diffraction have been analyzed to permit the identification of the structural units as Ga centered tetrahedra. The interconnection between the tetrahedra was found to be predominantly corner sharing.     

Concentration dependence of Dy3+:1.3 μm luminescence in Ge–Ga–Sb–Se glasses

The Ge₂₅Ga₅Sb₅Se₆₅ glasses, doped with 0.01, 0.05, 0.1, 0.2, and 0.5 mol% of Dy³⁺ ions are prepared and the concentration dependence of Dy³⁺:1.3 μm luminescence is investigated. Remarkable energy migration between Dy³⁺ ions occurs as its concentration is more than 0.05 mol%. With further increasing amount of Dy³⁺ ions, the decay time of the 1.3 μm fluorescence decreases rapidly. All the decays are simple exponential and possible regimes of the donor decay are discussed.     

Effect of lead oxide on optical properties of Dy3+ ions in PbO–H3BO3–TiO2–AlF3 glasses

The effect of lead oxide (PbO) on optical properties of Dy³⁺-doped PbO–H₃BO₃–TiO₂–AlF₃ (LBTAFDy) glasses is investigated. The LBTAFDy glasses were prepared with different PbO contents ranging from 30 to 60 mol%. The Judd–Ofelt intensity parameters (Ω_{λ = 2, 4, 6}) are obtained by the least square fit analysis. It is found that the Ω₂ parameter and yellow-to-blue intensity ratio (Y/B) of the Dy³⁺ emission depend on the PbO content in LBTAFDy glass. The structural asymmetry around the Dy³⁺ ion and the DyO covalency are responsible for the changes in Ω₂ parameter and Y/B ratio. The variation of decay time of ⁴F_9/2 emission level with the PbO content also supports the changes in structural asymmetry and DyO covalency in LBTAFDy glass.     

Electrical and dielectric properties of MnF2–ZnF2–NaPO3 glasses

Direct electrical conductivity and dependencies of complex electrical modulus vs. temperature and frequency have been measured on glasses from the MnF₂–ZnF₂–NaPO₃ system. These glasses are sensitive to atmospheric humidity and as a consequence, the electrical conductivity increases up to temperature of 50 °C. A hydrated layer is created by the effect of water and leads to the significant increase of the electrical conductivity in the case of 0MnF₂–20ZnF₂–80NaPO₃ glass. This behavior is governed by Arrhenius relation where the values of activation energy are increasing and values of the electrical conductivity are decreasing with the amount of MnF₂. Dielectric measurements show that a heterogeneous phase is formed in the bulk of glasses. This may be seen when plotting complex electrical modulus in the complex plane. The records made by the light microscope confirmed the occurrence of the other phase in the bulk of glasses.