Se-based Chalcogenide Glasses Research Articles

Lone-Pair-Enabled Polymorphism and Photostructural Changes in Chalcogenide Glasses.

S- and Se-based chalcogenide glasses are intrinsically metastable and exhibit a number of photo-induced effects unique to this class of materials, reversible photostructural changes and photo-induced anisotropy being major examples. These effects are usually interpreted in terms of the formation of valence alternation pairs and 'wrong' bonds. In this work, using density functional theory simulations, we demonstrate for the case example of As2S3 that a strong decrease in the optical band gap can be achieved if a polymorphic transformation of the local structure from orpiment to that of tetradymite takes place. For the formation of the latter, the presence of lone-pair electrons in near-linear atomic configurations is crucial. Our results represent a novel approach to understanding the photo-induced structural changes in chalcogenide glasses as being due to the presence of polymorphism, and will lead to their wider use in various photonic devices.

Study of High field conduction in Se based Chalcogenide glasses

The present work reports the study of high field conduction in thin films of Se90Ge10-x Inx (x=2,6) because high field conduction in chalcogenide glasses is affected by the presence of localised states at the band edges as well as the defect states present in the mobility gap.To measure the density of states in these thin films , space charge limited conduction technique is used. I-V characteristics have been measured at various fixed temperatures. An ohmic behaviour is observed at low electric fields upto 102V/cm. Superohmic behaviour is observed at high electric fields (103 -104 V/cm).High field conduction theory of space charge limited conduction for uniform distribution of localised states in the mobility gap fits well with the experimental data.Using this theory, the density of defect states near Fermi level is calculated for all glassy alloys.

Se-H-free As2Se3 fiber and its spectral applications in the mid-infrared.

The complete removal of the impurities like Se-H in Se-based chalcogenide glasses has been challenging in the development of highly transparent chalcogenide glass fiber. In this paper, several purification methods, including dynamic distillation, static distillation, and combined distillation method, were adopted with an aim of purifying arsenic selenide glass with ultra-low content of the impurities. The experimental results demonstrated that the Se-H can be completely eliminated in the arsenic selenide glass host and fiber without the introduction of any chloride. We further explored the applications of such low loss and Se-H-free chalcogenide glass fiber in the mid-infrared. It was found that, using such a Se-H free fiber, a flattened supercontinuum spectrum above the -30 dB level from 1.2 to 13 µm was generated from the Se-H free fiber with a 5.5 µm laser pumping. The sensitivity was found to be improved 5.1 times for CO2 gas in the 3 to 6 µm wavelength range.

Activation energy during the crystallization transition for Se-based chalcogenide glasses

This work aims to research the crystallization transition kinetics aspects for Se60Ge15As25 and Se60Ge15Sn25 compositions, utilized differential thermal analysis technique under the non-isothermal condition at various heating rates. Crystallization temperature (Tc) has been discovered heating rate and composition dependence. Heating rate dependence of Tc reveals the activation energy of crystallization (Ec) values according to various methods. Kissinger, modified Kissinger, Takhor, Baswell, Augis-Benntt, Mahadeven and Gao-Wang methods are applied to determine (Ec). The outcome shows an unsuitable Takhor method for determination of the crystallization parameters of the studied composition. The highest value of Ec is observed for Se60Ge15As25 composition. This result is confirmed by frequency factor Ko, crystallization rate factor K data and attributed to the effective bands energies with As and Sn addition to host composition. The transformation mechanisms have been examined by the values of Avrami exponent n and dimensionality of growth m. According to Avrami index n, the crystallization mechanism was interpreted as two-dimensional growth for Se60Ge15 with Sn addition and three-dimensional growth with As addition.

Third-order optical nonlinearity in Ge-Se-Te chalcogenide glasses

We have prepared GexSe10Te90-x glasses with a composition of x from 17.5 to 26.25 and measured their properties using various diagnosis tools. It was found that, all the glasses have a transmittance more than 40% at a wavelength range from 2 to 15 μm, and linear refractive index n0 decreases but optical bandgap energy Eg increases with decreasing Te contents in the glasses. We also analysed the evolution of n2 and β as a function of Ge content, both the evolution of n2 and β are close to the prediction by Sheik-Bahae et al. for optical nonlinearity of semiconductors. In all cases, the nonlinear optical refractive index n2 measured at 3.0 μm is larger than that at 2.5 μm due to the two-photon resonance effect, and a maximum nonlinear index is 2.46 × 10−13 cm2/W at composition of Ge17.5Se10Te72.5. Such larger nonlinearity around 10−13 cm2/W observed in the present paper is one order of the magnitude larger than that in S- and Se-based chalcogenide glasses, demonstrating potentials of Te-based glasses for the applications as mid- and far-infrared nonlinear optical devices.

High refractive index dispersion of compositionally optimized Ge-Ga-Sb-S sulfide glass for use as molded lens in the long-wavelength infrared range

In an effort to endow Ge-Sb-S sulfide glass with capability to transmit the long-wavelength infrared (LWIR) photons as well as to possess highly dispersive refractive indexes over the LWIR spectral range, we have compositionally adjusted ternary Ge-Sb-S glass prior to tuning quaternary Ge-X-Sb-S (X = Ga, Bi, In or Sn) glass. Among the constituent atoms of ternary Ge-Sb-S glass, Ge content turned out to exert the strongest influence not only on thermal and mechanical properties but also on infrared transmission edge. Specifically, glass transition temperature and Vickers hardness tended to be directly proportional to Ge content, but infrared transmission edge was blue-shifted upon increase of Ge content, simultaneously producing an additional multiphonon absorption peak at ~ 9 µm. As such, Ge-Sb-S glass containing Ge atoms less than ~ 15 at% was considered to feature applicability in LWIR range, which on the other hand suffers from relatively poor thermal and mechanical properties. In our experimental attempts on quaternary sulfide glasses performed to mitigate such deteriorations, presence of relatively small amount of Ga appeared to be most effective among the elements employed in this study as the fourth constituent. Moreover, only Ga atoms improved thermal stability with significantly increasing crystallization temperature. Quaternary Ge-Ga-Sb-S glass compositionally optimized in this study was then verified to be much more dispersive than typical Se-based chalcogenide glasses in the LWIR region.

Hardness Improvement of Chalcogenide Glasses

In and Bi were doped into 30Ge10Sb60Se and 27.5Ge12.5Sb60Se glasses to improve hardness. While Bi did not have any influence on hardness, In made 10% hardness improvement in 27.5Ge12.5Sb60Se glass. Over 8wt% In doping triggered crystallization of In2Se3 so that IR transmittance was degraded below 10%. In2Se3 crystallization was confirmed by XRD and FE-SEM. I. Introduction Recently, night vision system has been used in a various fields such as military, aircrafts, and cars. Since infrared lens components based on monocrystalline Ge or polycrystalline ZnSe were very expensive in the early days, it was used only for military application [1]. However, its applications have been widely expanded to civilian ones such as cars and even mobile phones by adapting moldable chalcogenide glasses which have low phonon energy, good thermal stability, and especially high infrared transparency up to 12 um [2]. Se-based chalcogenide glasses which have optical transparency up to 10um are assumed as attractive candidates for moldable chalcogenide glasses lens compared with S-based or Te-based chalcogenide glasses. Among several ternary Se-based glasses, especially, Ge-Sb-Se ternary glasses are considered as promising ones because they are thermally stable and non-toxic [3]. We have already investigated the optimum chalcogenide glass compositions for moldable lens in terms of IR transmittance, thermal property, and hardness [4]. Among them, hardness has an important role on lens fabrication process as well as final lens product. Here, we want to propose the way to improve hardness by adding additional element to the optimum compositions. II. Experiment Chalcogenide glasses have been made by the conventional fabrication method by rocking furnace. The starting materials (Ge, Sb, Se, In and Bi) were weighed and put into a silica ampule in a glove box filled with Ar gas. Glasses were melted in a 3 zone rocking furnace at 1000 °C for 12hrs and quenched into water followed by annealing. Synthesized glasses were cut and polished to measure properties such as Vickers hardness, IR transmittance (Perkin-Elmer, Spectrum 100), and surface morphology. III. Results and discussions The additional element which was chosen to improve hardness was determined in terms of binding energy and tendency of glass forming ability. In (Indium) and Bi (Bismuth) were doped with the optimum composition glasses such as 30Ge10Sb60Se and 27.5Ge12.5Sb60Se. Based on the reference literature, In and Bi were doped by 3, 5wt% and 8wt%, respectively. Each glass was cut and polished in the upper part, middle part, and lower part to confirm the homogeneity of glass. IR transmittance and Vickers hardness were measured for each sample. Since each sample from one glass showed almost similar IR transmittance and Vickers hardness, synthesized glasses seem to be homogeneous. The tendency of In and Bi doping on IR transmittance and Vickers hardness was investigated more detail. IR transmittance of In and Bi doped 30Ge10Sb60Se glasses showed almost similar value except 5wt% In doped glass. 5wt% In doped 30Ge10Sb60Se glass showed lower than 50% IR transmittance. However, doping of In and Bi has not an effect on Vickers hardness at all. In and Bi doped 27.5Ge12.5Sb60Se glasses showed a little different trend. Vickers hardness of Bi doped 27.5Ge12.5Sb60Se glasses did not show any improvement. On the other hand, 3wt% and 5wt% In doped 27.5Ge12.5Sb60Se glasses showed about 10% Vickers hardness improvement while IR transmittance property remains over 60%. IR transmittance of 8wt% In doped 27.5Ge12.5Sb60Se glass decreased below 10%, which means In should be doped under 8wt%. In order to confirm the reason of IR transmittance decrease, XRD and FE-SEM analyses were done. According to XRD results, 8wt% In doped 27.5Ge12.5Sb60Se glass showed In2Se3 peak while other glasses did not show any other sharp peaks related to crystallization. In addition, small particles which are related to In2Se3 crystallization were observed on the surface of 8wt% In doped 27.5Ge12.5Sb60Se glass in FE-SEM image References [1] X.H. Zhang, Y. Guimond, Y. Bellec, J. Non-Cryst. Solids 326&327 (2003) 519 [2] E. Guillevic, X.H.Zhang, T. Pain, L. Calvez, J.L. Adam, J. Lucas, Opt. Mater. 31 (2009) 1688 [3] D.R. Goyal, A.S. Maan, J. Non-Ctryst. Solids 183 (1995) 182 [4] J.H. Lee, W.H. Lee, J.K. Park, J.H. Yi, S.Y. Shin, B.J. Park, B. So, J. Heo, J.H. Choi, H.J. Kim, Y.G. Choi, J. Non-Ctryst. Solids, to be published (2016) Figure 1

Improvements on the optical properties of Ge–Sb–Se chalcogenide glasses with iodine incorporation

Decreasing glass network defects and improving optical transmittance are essential work for material researchers. We studied the function of halogen iodine (I) acting as a glass network modifier in Ge–Sb–Se-based chalcogenide glass system. A systematic series of Ge20Sb5Se75−xIx (x=0, 5, 10, 15, 20at.%) infrared (IR) chalcohalide glasses were investigated to decrease the weak absorption tail (WAT) and improve the mid-IR transparency. The mechanisms of the halogen I affecting the physical, thermal, and optical properties of Se-based chalcogenide glasses were reported. The structural evolutions of these glasses were also revealed by Raman spectroscopy and camera imaging. The progressive substitution of I for Se increased the optical bandgap. The WAT and scatting loss significantly decreased corresponding to the progressive decrease in structural defects caused by dangling bands and structure defects in the original Ge20Sb5Se75 glass. The achieved maximum IR transparency of Ge–Sb–Se–I glasses can reach up to 80% with an effective transmission window between 0.94μm and 17μm, whereas the absorption coefficient decreased to 0.029cm−1 at 10.16μm. Thus, these materials are promising candidates for developing low-loss IR fibers.

Spatial distribution of rare-earth ions in Se-based chalcogenide glasses with or without Ga

Measured lifetime of the ( 3F 3, 3F 4) level of Pr 3+ ions doped in representative Se-based chalcogenide Ge–Sb–Se glasses peaked at the mean coordination number of ∼2.67, indicating that inter-ionic distance between Pr 3+ dopants became maximized on the average at such particular host compositions. However, this phenomenon was not observed when Ga was further introduced. It has been verified from Ga K-edge EXAFS spectroscopic analysis that a Ga atom has four Se atoms as its nearest neighbors in the Ge–Sb–Se glasses doped with Pr. The Ga–Se bonds are less covalent than other heteropolar chemical bonds, and thereby positively ionized rare-earth elements would be located preferentially next to the GaSe 4 units, acting as charge compensators or network modifiers. We presume that there is a negligible structural and chemical correlation between a rare-earth ion and its next-nearest neighbors on their sites in the typical covalent chalcogenide glasses without Ga, and as a result spatial distribution of rare-earth ions would depend on changes of the free volume accompanied with the structural phase transitions on a medium-range scale from two-dimensional layers to three-dimensional networks. In selenide glasses with Ga, however, the empirical connection disappears due to the structural correlation between rare-earth ions and the GaSe 4 tetrahedra.

Wavelength dispersion of Verdet constants in chalcogenide glasses for magneto-optical waveguide devices

The wavelength dispersion of the Verdet constants of bulk As–S, As–Se–S, Ge–As–Se and Ga–La–S-based chalcogenide glasses has been investigated at wavelengths between 675 and 1550 nm. Ge 33As 12Se 55 was found to have the highest Verdet constant, 0.0485 min/G.cm at 1550 nm, 30 times that of silica. The high Verdet constant of Ge 33As 12Se 55 is related to its smaller band gap energy compared with the other glasses. Further improvement of the Verdet constants of the Ge–Se-based chalcogenide glasses by engineering their compositions could make them promising materials for integrated magneto-optical devices.

Large Kerr effect in bulk Se-based chalcogenide glasses

High-speed optical communication requires ultrafast all-optical processing and switching capabilities. The Kerr nonlinearity, an ultrafast optical nonlinearity, is often used as the basic switching mechanism. A practical, small device that can be switched with ~1-pJ energies requires a large Kerr effect with minimal losses (both linear and nonlinear). We have investigated theoretically and experimentally a number of Se-based chalcogenide glasses. We have found a number of compounds with a Kerr nonlinearity hundreds of times larger than silica, making them excellent candidates for ultrafast all-optical devices.

Wavelength trimming by external light irradiation-post-fabrication lasing wavelength adjustment for multiple-wavelength distributed-feedback laser arrays

Oscillation wavelength of distributed-feedback (DFB) lasers is easily affected by small variation in device parameters, and therefore, prescribing oscillation wavelength is very difficult. This insufficient wavelength reproducibility limits the device yield, specifically, in multiple-wavelength DFB laser arrays whose element needs to have lasing wavelength that matches pre-defined wavelength-division-multiplexed (WDM) channels. In this paper, we describe a novel concept to manage this problem, namely, "wavelength trimming." Here, the oscillation wavelength error is corrected after the device fabrication without using external active control circuitry. In this particular demonstration, we have used Se-based chalcogenide glass film having photo-induced refractive index change as a part of the laser waveguide, and demonstrated the wavelength trimming of 0.14 nm at 1.55 /spl mu/m in an index-coupled DFB laser by He-Ne laser irradiation.

Wavelength trimming technology for multiple-wavelength distributed-feedback laser arrays by photo-induced refractive index change

The authors propose a novel post-fabrication wavelength-error correction method in distributed-feedback (DFB) laser arrays without using external active control circuitry, namely ‘wavelength trimming technology’. Se-based chalcogenide glass has been used which has a refractive index change of ~1% induced by light irradiation as a part of a waveguide of 1.55 µm DFB laser and wavelength trimming of 0.14 nm is demonstrated.

Index of refraction, dispersion, bandgap and light scattering in GeSe and GeSbSe glasses

The fundamental optical properties of Se-based chalcogenide glasses were investigated. Glass compositions of Ge-Se and Ge-Sb-Se were fabricated and characterized. The index of refraction, material dispersion, bandgap absorption, optical bandgap, and intrinsic light scattering are reported for these glasses. A Sellmeier formalism was used to obtain the oscillator strengths and excitation energies of the glasses. The estimated intrinsic properties of the glasses are reported and the influence of composition on the optical properties was established.

Variation of band gap in Se-based chalcogenide glasses

The random network model for amorphous alloys proposed by White has been developed for the system irradiated with light. The model suggests that the photobleaching in GeSe 2 film and the photodarkening in AsSe film may be due to change in the number of the bonds.