Karel Palka

Preparation of arsenic sulfide thin films for integrated optical elements by spiral bar coating

We report on the preparation of thin As35S65 films from their amine based solutions by a spiral bar coating technique on flexible PET substrates and the direct writing of subwavelength surface corrugated gratings with a period of 350 nm into these films by excimer laser interference lithography. The structural and optical properties of bar coated As35S65 glass are investigated in detail and compared with those of samples fabricated by vacuum thermal evaporation. The polarization dependent spectral filtering properties of the guided mode resonance devices built by the waveguiding thin films and the surface relief gratings written by a single laser pulse are presented finally.

Structure and properties of spin-coated Ge 25 S 75 chalcogenide thin films

Amorphous chalcogenide thin films of Ge25S75 composition have been deposited by spin-coating technique. Optical properties of thin films were investigated by spectroscopic ellipsometry in UV-MIR spectral range. Obtained results prove increase of thin films refractive index in the transparent region and decrease of their thickness with increasing annealing temperature implying densification of the glass structure. Short wavelength absorption edge is shifting to lower energies (red shift) with increasing annealing temperature. Decreasing organic molecules content with increasing temperature of annealing was observed in MIR part of extinction coefficient and verified by Raman spectroscopy and EDS. Raman spectra also gave evidence of thermo-induced structural polymerization and decomposition of organic salts molecules yielding thin films with structure similar to the structure of the source bulk glass.

Exposure enhanced photoluminescence of CdS0.9Se0.1 quantum dots embedded in spin-coated Ge25S75 thin films

Semiconductor quantum dots (QDs) are well known photoluminescent materials. Their potential practical applications depend on their physico-chemical and luminescent properties and also on the properties of hosting material. To ensure that QDs retain their photoluminescence during the preparation of a suitable solid composite form, the solution based casting techniques with deposition at lower temperatures are usually used. In our work, we have doped an inorganic Ge25S75 chalcogenide glass matrix with synthesized CdS0.9Se0.1 QDs and prepared thin films by the solution based spin-coating technique. In comparison with commonly used polymers the Ge25S75 chalcogenide glass thin films a possess high refractive index and wide VIS-NIR-MIR optical transparent region. We also report on the phenomenon of significant UV exposure induced increase of doped thin film photoluminescence intensity which can be exploited in local photo-induced photoluminescence enhancement of doped chalcogenide glass thin films.

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.

Spectroscopic ellipsometry characterization of spin-coated Ge25S75 chalcogenide thin films

Abstract Spectroscopic ellipsometry study on spin-coated non-toxic Ge25S75 thin films annealed at different temperatures were conducted. Multi sample analysis with two sets of samples spin-coated onto soda-lime glass and onto silicon wafers was utilized. Optical constants (refractive index n and extinction coefficient k) of these films were determined from ellipsometric data recorded over a wide spectral range (0.05–6 eV). Different parametrization of Ge25S75 complex dielectric permittivity which consists of a Tauc-Lorentz or Cody-Lorentz oscillator describing the short wavelength absorption edge, a Lorentz or Gauss oscillators describing phonon absorption or optically active absorption of alkyl ammonium germanium salts in the middle infrared part of spectra is discussed. Using a Mott-Davis model, the decrease in local disorder with increasing annealing temperature is quantified from the short wavelength absorption edge onset. Using the Wemple-DiDomenico single oscillator model for the transparent part of the optical constants spectra, a decrease in the centroid distance of the valence and conduction bands with increasing annealing temperature is shown and increase in intensity of the inter-band optical transition due to annealing temperature occurs. Intensity of absorption near 3000 cm−1 could be used as alternative method to evaluation of quality of prepared films.

Solution-processed Er3+-doped As3S7 chalcogenide films: optical properties and 1.5 μm photoluminescence activated by thermal treatment

We report on the optical properties of Er-doped As3S7 chalcogenide films prepared using the two step dissolution process utilizing the As3S7 glass dissolved with propylamine and by further addition of the tris(8-hydroxyquinolinato)erbium(III) (ErQ) complex acting as an Er3+ precursor. Thin films were deposited by spin-coating, thermally stabilized by annealing at 125 °C and further post-annealed at 200 or 300 °C. The post-annealing of films at 200 °C and 300 °C densifies the films, improves their optical homogeneity, and moreover activates the Er3+:4I13/2 → 4I15/2 (λ ≈ 1.5 μm) PL emission at pumping wavelengths of 808 and 980 nm. The highest PL emission intensity was achieved for As3S7 films post-annealed at 300 °C and doped with ≈1 at% of Er which is beyond the normal Er3+ solubility limit of As–S melt-quenched glasses. The solution-processed deposition of the rare-earth-doped chalcogenide films utilizing the organolanthanide precursors has much potential for application in printed flexible optoelectronics and photonics.

Photoresponse of inorganic-organic thin film composites based on chalcogenide glasses

Spin coated chalcogenide thin films have different structural and chemical properties than the films obtained by traditional methods such as thermal evaporation or sputtering. The solution-based method provides lower sensitivity of glass matrix to the influence of bandgap and superbandgap light. This property is very useful for non-linear optical applications based on high transparency of these materials in infrared spectral region. Arsenic selenide spin coated thin films were obtained by chemical dissolution of bulk glasses in ethylenediamine. The influence of preparation conditions, especially the annealing temperatures at the final stage of thin films synthesis, on in-situ kinetics of photodarkening (bleaching) at various energies and intensities of UV-VIS light was studied. It was found that at certain annealing conditions only transient photoinduced effects can be obtained by eliminating metastable kinetic component. Mechanisms of the photoinduced effects are discussed based on the parameters of relaxation functions.Spin coated chalcogenide thin films have different structural and chemical properties than the films obtained by traditional methods such as thermal evaporation or sputtering. The solution-based method provides lower sensitivity of glass matrix to the influence of bandgap and superbandgap light. This property is very useful for non-linear optical applications based on high transparency of these materials in infrared spectral region. Arsenic selenide spin coated thin films were obtained by chemical dissolution of bulk glasses in ethylenediamine. The influence of preparation conditions, especially the annealing temperatures at the final stage of thin films synthesis, on in-situ kinetics of photodarkening (bleaching) at various energies and intensities of UV-VIS light was studied. It was found that at certain annealing conditions only transient photoinduced effects can be obtained by eliminating metastable kinetic component. Mechanisms of the photoinduced effects are discussed based on the parameters of rela...

Mechanistic investigation of the sulfur precursor evolution in the synthesis of highly photoluminescent Cd0.15Zn0.85S quantum dots

Semiconductor quantum dots (QDs) with stable and wavelength-tunable photoluminescence (PL) are very promising emitters for various photonic and optoelectronic applications. In this paper, we describe a comparison of four synthetic approaches for highly photoluminescent blue-emitting Cd0.15Zn0.85S QDs. (Z)-1-(Octadec-9-enyl)-3-phenylthiourea, initially prepared from phenyl isothiocyanate and oleylamine, was used as the source of sulfur. Environmentally friendly and commercially available N,N′-disubstituted thiourea in combination with well-known methods is a suitable precursor for the highly reproducible synthesis and further large-scale production of ternary Cd0.15Zn0.85S QDs. This study was carried out to examine the mechanism of interaction between disubstituted thiourea and metal carboxylates in one of two tautomeric forms under the influence of oleylamine, which was taken as a base in the synthesis of the QDs by hot-injection and one-pot methods. Chemical and thermal decompositions of the QDs were performed to get information about the amount and composition of organic ligands in their shells. To elucidate the mechanisms of QD formation, the organic products were studied by NMR. Optical studies showed that the prepared nanomaterials exhibit narrow emission peaks with a full width half maximum (FWHM) of around 19–33 nm and a very small size of nanocrystals (1.59–3.53 nm).

Spectroscopic ellipsometry characterization of sine-like surface relief Ni gratings

Spectroscopic ellipsometry was employed for determination of structural parameters of holographic Ni grating: its period and profile depth. Native oxide overlayer was also taken into account. Moreover slight deviation of sine-like profile was considered and analyzed. Obtained results were compared with conventional complementary methods as scanning electron microscopy, atomic force microscopy and optical microscopy. Advantages and disadvantages of all above mentioned approaches were presented.