Lukas Strizik

Atomic Layer Deposition Al2O3 Coatings Significantly Improve Thermal, Chemical, and Mechanical Stability of Anodic TiO2 Nanotube Layers

We report on a very significant enhancement of the thermal, chemical, and mechanical stability of self-organized TiO2 nanotubes layers, provided by thin Al2O3 coatings of different thicknesses prepared by atomic layer deposition (ALD). TiO2 nanotube layers coated with Al2O3 coatings exhibit significantly improved thermal stability as illustrated by the preservation of the nanotubular structure upon annealing treatment at high temperatures (870 °C). In addition, a high anatase content is preserved in the nanotube layers against expectation of the total rutile conversion at such a high temperature. Hardness of the resulting nanotube layers is investigated by nanoindentation measurements and shows strongly improved values compared to uncoated counterparts. Finally, it is demonstrated that Al2O3 coatings guarantee unprecedented chemical stability of TiO2 nanotube layers in harsh environments of concentrated H3PO4 solutions.

Dynamics of upconversion photoluminescence in Ge–Ga–S: Er3+: application of quadrature frequency resolved spectroscopy

Quadrature frequency resolved spectroscopy (QFRS) on green (~550 nm) upconversion photoluminescence (UCPL) of Ge–Ga–S: Er3+ glasses pumped at 975 nm revealed double-peaked spectra with long lifetime τ1 ranging from 0.2 to 2 ms and short lifetime τ2 ≈ several tens of μs. The results are analysed in terms of the transfer function derived by linearizing rate equations for a three-level model. The τ1 component is attributed to the relaxation at the intermediate level 4I11/2 of Er3+ ions and the τ2 component, to that at the upper 4S3/2 manifold. The dominance of energy transfer upconversion over excited state absorption in the UCPL manifest itself as a greater dependence of τ1 on the pump power and a lower ratio of the components of τ2 to τ1 in the QFRS spectra of a heavily Er-doped sample.

In-situ study of athermal reversible photocrystallization in a chalcogenide glass

The time-resolved Raman measurements reveal a three-stage mechanism of the photostructural changes in Ge25.0Ga9.5Sb0.5S65.0 (containing 0.5 at. % of Er3+) glass under continuous-above-bandgap illumination. These changes are reversible and effectively athermal, in that the local temperature rises to about 60% of the glass-transition temperature and the phase transitions take place in the glass/crystal and not in an equilibrium liquid. In the early stages of illumination, the glassy-network dimensionality changes from a predominantly 3-D to a mixture of 2-D/1-D represented by an increase in the fraction of edge-sharing tetrahedra and the emergence of homonuclear (semi)metallic bonds. This incubation period of the structural rearrangements, weakly thermally activated with an energy of ∼0.16 eV, facilitates a reversible photocrystallization. The photocrystallization rate in the glass is comparable to that achieved by thermal crystallization from supercooled liquid at large supercooling. Almost complete re-amo...

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.

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.

Influence of thermal history on the photostructural changes in glassy As15S85 studied by Raman scattering and ab initio calculations

Photostructural changes—the hallmark of non-crystalline chalcogenides—are in essence the basis of a number of photoinduced effects, i.e., changes of their physical properties, which are exploited in a variety of applications, especially in photonics and optoelectronics. Despite the vast number of investigations of photostructural changes, there is currently lack of systematic studies on how the thermal history, which affects glass structure, modifies the extent of photostructural changes. In this article, we study the role of thermal history on photostructural changes in glassy As15S85. This particular sulfur-rich composition has been chosen based on the colossal photostructural response it exhibits under near-band gap light irradiation, which inherently originates from its nanoscale phase-separated nature. To control the thermal history, the glass was quenched to various temperatures and each of these quenched products was annealed under four different conditions. Off-resonant Raman scattering was used t...

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.

Up-Conversion in Er3+-Doped Ge25Ga5Sb5S65 Chalcogenide Glass for Enhancement of Silicon Solar Cell Efficiency

Er³⁺-doped Ge₂₅Ga₅Sb₅S₆₅ chalcogenide glass was studied as a potential material for up-conversion application to enhancement of silicon solar cell efficiency. Thermal properties were studied via DSC measurement, optical properties via variable angle spectroscopic ellipsometry and photoluminescence measurement. The host chalcogenide glass shows good thermal, chemical and physical properties. The band gap energy is ~2.23 eV which allows to emit green and red luminescent light from ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 4f-4f transitions of Er³⁺ ions under 800 nm pumping with Ti-sapphire tunable laser.