Bozena Frumarova

Pulsed laser deposition of pure and praseodymium-doped Ge–Ga–Se amorphous chalcogenide films

Abstract Pure and praseodymium-doped thin films of Ge30Ga5Se65 amorphous system were prepared by the pulsed laser deposition (PLD) technique. The composition of the prepared films was close to the composition of the used targets of bulk chalcogenide glass. The structure of the prepared films was also close to that of the targets as shown by the Raman spectra. The annealing of films shifted the position of the absorption edge to higher energies, which is explained by chemical homogenization of the films due to interaction of fragments of the evaporated material. Two luminescence bands near 1340 and 1610 nm were observed in the emission spectra of praseodymium-doped Ge–Ga–Se thin films. They were assigned to the radiative transitions between discrete energy levels of Pr3+ ions, 1G4–3H5 and 3F3–3H4, respectively. The luminescence intensity of ablated films was lower than that of bulk glasses. It increased after annealing of the films.

Synthesis and physical properties of the system (GeS2)80−x(Ga2S3)20:xPr glasses

Abstract High purity (GeS2)80−x(Ga2S3)20·xPrCl3 (x= 1,2,3), (GeS2)79(Ga2S3)20Pr6O11 glasses were prepared and their basic thermal and optical properties were detemuned. The glass transition temperature Tg is in the region 399–404°C. The glass-forming criteria (ΔT ∈ (123–128°C), Hr ∈ (0.59–0.66), S ∈ (2.37–3.29) are changed by Pr doping only a little. The short-wavelength absorption edge lies near 2.7 eV, the doping by Pr creates new absorption bands which can be assigned to the 3H4-3H6, 3H4-3F3, 3H4-3F4, 3H4-3P0 and 3H4-3P1 electron transitions. The experimentally found oscillator strengths calculated from absorption spectra lies between those of Pr doped halide and chalcohalide glasses. The long-wavelength absorption edge was found near 800–1000 cm−1 and it corresponds to multiphonon Ge-S and Ga-S vibrations. The far-IR diffuse reflectance spectra were measured and the spectrum revealed by Kubelka-Munk method. The spectrum was deconvoluted into several bands which can be assigned to GeS4 and GaS4 tetrahedra vibrations. The narrow luminescence bands corresponding to electron transitions in Pr3+ ions (20000, 17857, 15873, 15220, 14326, 13947 and 13459 cm−1) with the most intensive band near 15220 cm−1 were found. These bands can be assigned to the transitions from the 3P0 and 1D2 levels to 3F4, 3F3, 3F2, 3H6, 3H5 and 3H4 levels. The most intensive band corresponds to the 3P0-3F2 transitions.

Intense near-infrared and midinfrared luminescence from the Dy3+-doped GeSe2–Ga2Se3–MI (M=K, Cs, Ag) chalcohalide glasses at 1.32, 1.73, and 2.67 μm

The intense 1.32, 1.73, and 2.67 μm near-infrared and midinfrared emissions were observed from the Dy3+-doped GeSe2–Ga2Se3–MI (M=K, Cs, Ag) chalcohalide glasses. These glasses are red light transparent therefore can be pumped by a semiconductor lasers operating at ∼808 nm. The 2.67 μm emission has not been reported yet which corresponds to an absorption minimum in fluoride fibers and can be very useful for long distance communications. The intensity of emissions is very sensitive to the local chemical environment of Dy3+ ions embedded in these metal halide modified glasses. A plausible correspondence between the emission intensity and the average oscillator strength was found.

In-situ measurement of reversible photodarkening in ion-conducting chalcohalide glass

We report the kinetics of below band-gap light induced photodarkening in (80-x)GeS(2)-20Ga(2)S(3)-xAgI (x = 0 and 20 mol %) bulk chalcogenide glasses by measuring the time evolution of transmission spectra at every 10 milliseconds. The results prove clearly the enhancement of photosensivity upon doping of AgI compound in glasses. It is interesting to find that PD observed in AgI-doped glass totally disappears two hours later after the laser exposing even at room temperature. In significant contrast to 80GeS(2)-20Ga(2)S(3) glass that the metastable part of PD remains for a long time. We expect such a fast auto-recovery property in AgI-doped glass can be utilized for optical signal processing.

Reversible photoinduced change of refractive index in ion-conducting chalcohalide glass

When irradiated by the focused Ar+ ion laser of below band-gap photon energy (2.41 and 2.54eV), a large increase of refractive index (e.g., Δn=6% at 1550nm) was observed in 60GeS2–20Ga2S3–20AgI bulk glass (with bandgap of 2.71eV). We found it surprisingly that such a large Δn quickly smeared out after the illumination even at room temperature, i.e., the refractive index will return to almost initial value within only 2h. It is fairly rare among chalcogenides ever reported. The plausible correlation between the photorefraction effect and the ion-conducting property of glasses was also suggested.

Conductivity study on GeS2-Ga2S3-AgI-Ag chalcohalide glasses

A new kind of ion-conducting glasses based on GeS2-Ga2S3-AgI system is prepared. A relatively large amount of silver can be dissolved into this kind of glass system, and the obtained glasses are still transparent in the red part of the visible spectrum. Only a three times increase in the silver concentration can lead to approximately two hundred times increase in the ionic conductivity. The structural contributions to the ionic conductivity of the glasses are discussed. The present glasses show potential to be used as solid state electrolyte.

Photoinduced changes of the structure and index of refraction of amorphous As-S films

Abstract The irreversible and reversible photoinduced changes of the structure and physical properties of stoichometric and non-stoichiometric As x s 100− x ( x = 38, 40 ) thin films were studied. The changes in intensities of Raman bands were interpreted in terms of changes of shortrange order. The illumination and/or annealing of fresh-evaporated As S system thin films change the as 4 s 4 and S n , contents as well as the densities of As As and S S bonds. Illumination and annealing shift the short wavelength absorption edge towards lower energies and changes the index of refraction. The energy dependence of the index of refraction, n , can be described by the Wemple-DiDomenico dispersion relationship n 2 (ħω) − 1 = E o E d /[ E o 2 − (ħω) 2 ], from which the single oscillator energy, E o and the dispersion energy, E d , were determined. The dependence of E o , E d , n , and of the thickness of the sample d on the stoichiometry, illumination and annealing are also discussed.

Crystalline and Amorphous Chalcogenides, High-Tech Materials with Structural Disorder and Many Important Applications

The paper reviews and discusses crystalline, nanocrystalline, glassy and amorphous chalcogenides and their thin films and fibres, their preparation, structure, properties, changes and applications in optics, optoelectronics and electronics, data storage and sensors with accent on recent data and progress. The area of interest is so broad that only some materials and processes could be discussed in detail, and a lot of data were chosen for the sake of illustration only.

Physico-chemical and optical properties of Er3+-doped and Er3+/Yb3+-co-doped Ge25Ga9.5Sb0.5S65 chalcogenide glass

Abstract We investigated the physicochemicаl properties, structure and optical properties of the Ge25Ga9.5Sb0.5S65: Er3+/Yb3+ glasses. The Judd-Ofelt theory was used to calculate the intensities of the intra-4f electronic transitions of Er3+ ions. We observed the upconversion photoluminescence (UCPL) at 530, 550, 660 and 810 nm under 980 nm excitation. In the Ge25Ga9.5Sb0.5S65: 0.1 at.% Er3+, we found that the Stokes photoluminescence (PL) at the green spectral region excited by the 490 and 532 nm laser is only ≈5 times higher than the UCPL emission under 810 or 980 nm excitation making these materials attractive for UCPL applications. The addition of 0.1–1 at.% of Yb3+ into Ge25Ga9.5Sb0.5S65: 0.1 at.% Er3+ glass reduces the UCPL as well as the Er3+ ≈1.5 μm emission intensity probably due to the reabsorption processes of the excitation light and concentration quenching. However, the observed Er3+: 4S3/2→4I13/2 (≈850 nm) emission in the Ge25Ga9.5Sb0.5S65: 0.1 at.% Er3+ sample populates the 4I13/2 level, which promises the using of this material for the 1.5 μm optical amplification.

Influence of Ag Doping on Physico-Chemical Properties of the Ge28Sb12Se60 Chalcogenide Glassy Matrix

Thermal, optical and electrical properties of the Agx(Ge28Sb12Se60)100x system (for x = 0 to 20) are systematically studied using various characterization techniques. In the present study, we have shown the reproducibility of the current results with the previously published literature and several novel results are also presented. The impedance data for the understanding of electrical properties of the materials has been analyzed using the random-walk (RW) model. We observed that, Ag playing two different concentration dependent roles i.e. above and below the 5% of Ag concentration, which is confirmed by the Raman analysis. The anomalous behaviors of electrical conductivity, optical and thermal properties with increasing Ag concentrations are explained by the role of Ag in the structural modification. We compared the diffusion coefficient (D), obtained from the RW model analysis with the experimental data(obtained from tracer diffusion) and found diffusion coefficient (D), obtained from the RW model are in good agreement corresponded with the experimental values. We also found a major change in conductivity of insulating Ge28Sb12Se60 (~ 10-14 S·cm-1) to a fast ionic conductor for Ag15(Ge28Sb12Se60)85 (~ 10-6 S·cm-1), i.e., a nine orders of magnitude. We demonstrated that the random-walk model can replacea time consuming and expensive tracer diffusion method for the determination of D. The present article helps to understand the ion conduction mechanism in disordered / amorphous materials.