The importance and relevance of creating materials with the ability to absorb photons from the environment or sunlight and subsequently convert them into photons of the bactericidal range of the spectrum (220-280 nm) are due to the need to create self-sterilizing surfaces without the use of ultraviolet lamps. The use of such surfaces can help to permanently reduce the content of adsorbed microbes. The intense luminescence of Pr³⁺ ions in a wide range of wavelengths, including in the UV-C range (200-280 nm), allows them to be used as activator ions in the creation of materials emitting in the ultraviolet region.

The SrO-CaO-MgO-SiO₂ glasses doped with Pr³⁺ ions were synthesized. We investigated the absorption and luminescence spectra of the glass samples in the wide spectral range, their luminescence lifetimes, the Up-converted UVC luminescence using a 444 nm diode laser, and the effect of temperature on the spectral properties of the glasses.

The up-convection luminescent radiation in the UV region nm with the maximum at 275 nm in the doped glasses upon excitation by lower-frequency radiation was obtained. The luminescence of Pr³⁺ ions in the glasses corresponded to the spectral maxima in blue, reddish-orange, and near-infrared spectral regions. The results of the investigation of Pr³⁺ ions' luminescence as a temperature function show that temperature elevation gives rise to a moderate lowering of Pr³⁺ ion luminescence in the visible region and emission band extension, especially at longer wavelengths. The effect of the increasing temperature on the ³Н₄→³Р₂ absorption band is insignificant. Thus, excitation of the up-converted emission of Pr³⁺ ions can be efficient even at a high laser diode power.

Synthesized glasses can be used as materials for photonic applications, including in the creation of light-emitting diodes and the development of UV self-sterilizing surfaces.

The study is described in more detail in [Materials,Vol.17(2024)1771].

Plasma electrolytic oxidation (PEO) is an electrochemical process recognized as one of the most effective techniques for functional coatings. In this process, a high voltage is applied to the electrolyte, resulting in a plasma discharge on the surface of a light metal alloy substrate, forming a hard and dense ceramic coating. We incorporated several powders of well-known semiconductor photocatalysts, including TiO₂-graphene, 2D-WO₃, 2D-MoO₃, and 2D-Bi₂WO₆, as additives to the electrolyte. Our objective was to produce plates with coatings of the aforementioned 2D photocatalysts, which show high potential for degrading various organic pollutants in water.

The photocatalysis process we utilized is based on reactions that occur on the coating surfaces in the presence of water and sunlight. Specifically, under UV-VIS light, electrons and holes are photogenerated in the semiconductor PEO-layer. These, in turn, react with dissolved oxygen, hydroxyl ions, and water to form reactive oxygen species, which effectively degrade pollutants into simpler molecules.

We tested coatings with homogeneous, single layers of photocatalysts as well as combinations forming multilayer structures. As a result, the obtained layers demonstrated high photocatalytic activity against organic compounds under UV-VIS irradiation. Our research focused on preparing highly porous coatings composed of 2D structures with enhanced photocatalytic properties, suitable for easy application in water remediation.

Photonic Crystal fibres have been gaining attention since 1995, when the first PCF was introduced. The flexibility to alter various properties of a PCF just by varying its geometrical properties, like the hole size, pitch, or number of rings, makes it versatile and more convenient to use as compared to normal optical fibres. We report a chalcogenide glass (As2Se3)-based photonic crystal fibre with a solid core. The proposed PCF has an ultra-high numerical aperture value reaching up to 1.82 for the explored wavelength range of 1.8-10 μm in the mid-infrared region. With this, the PCF has a high light-gathering capacity. With negative dispersion reaching up to approx. -2000 ps/km-nm at 4.8 micrometres, the fibre acts as a dispersion compensating fibre, with confinement loss being close to zero for higher values of wavelength. The value of dispersion is significantly less due to the regular variation in the size of the holes in the transverse direction, as compared to the design when there is no gradation. The value of the numerical aperture increases as the pitch increases from 0.92 to 0.96 and then to 1 micrometre, at a particular wavelength value. The design has been optimized with the appropriate value of the perfectly matched layer to obtain the best results.

In this work, we investigate the integration of graphene nanoplatelets (GNPs) with amorphous germanium (Ge) substrates. The unique properties of amorphous Ge, such as its ability to introduce localized energy states and disorders, significantly influence the electronic interactions within the composite material. These peculiarities, including density variations and distinct optical properties, are crucial in determining the overall behavior of the GNPs–amorphous Ge composite.

Germanium films were deposited onto glass substrates using DC magnetron sputtering, followed by the deposition of GNPs through a dip-coating process. The optical properties of these composites were meticulously characterized using Variable Angle Spectroscopic Ellipsometry (VASE) across a wavelength range of 300–1000 nm and incident angles between 50° and 70°. A comprehensive spectral fit was achieved using a generalized oscillator model incorporating three Gaussian oscillators.

Our findings reveal a significant alteration in the optical properties resulting from the interaction between GNPs and the amorphous Ge substrate. This interaction likely involves the merging of electronic states from both materials, leading to an increased density of states at the Fermi level and enhanced optical absorption. The resulting composite exhibited an improved refractive index and extinction coefficient, suggesting a stronger light–matter interaction.

These enhanced optical properties underscore the potential of GNPs–amorphous Ge composites in various optoelectronic applications. This study provides a deeper understanding of the interaction mechanisms at play, paving the way for the development of advanced materials with tailored optical properties for specific technological applications.

Introduction

Metamaterial-based optical filters are commonly used to address the ‘blue-shift’ issue as they exploit the absorption of the material and interplays of photonic crystals. A shift-free bandpass filter based on a silicon nanosphere (SiNP) with gold as a core--shell array was developed. However, the single-layer design’s blocking performance is relatively weak due to inadequate absorption and scattering. Moreover, it faces pronounced difficulties with transverse electric (TE) polarized light at a high angle of incidence (AOI); therefore, an extra AOI insensitive edge-filter design was employed. The optimized bandpass metamaterial filter demonstrates high insensitivity to AOI and stronger blocking performance, evidenced by its high optical density (OD = 2.35).

Method

A systematic design protocol that combined fullwave simulation software (CST) and transfer-matrix-based thin-film filter design software (Essential Macleod, ESM) was employed to optimize the design.

Results

The fundamental single layer is composed of infinite unit cells in a primitive cubic lattice configuration. Each unit cell comprises silicon nitride (SiN) as the host medium and a SiNP with a gold shell. To address the poor blocking performance problem, a second meta-layer was introduced. Furthermore, to remove the undesired peaks observed at high AOI, an AOI insensitive edge filter was introduced. It incorporates “H/2 L H/2” units, where H and L denote the high (Amorphous silicon) and low (SiN) refractive index materials, respectively, each with a quarter wavelength thickness. The final optimized design significantly enhances the OD up to 2.35 for TE polarization and 1.75 for transverse magnetic polarization.

Conclusion

In conclusion, a multi-layer, wide-angle, shift-free bandpass filter was successfully designed using the combined design protocol and further optimized by introducing an AOI insensitive edge filter. It demonstrates high OD in the stopband at all AOI due to the introduction of the second meta-layer and edge-filter design.

Inorganic nanocrystals doped with transition metal ions combine several advantageous features: (1) high chemical and photochemical stability with (2) efficient luminescence resulting from the high absorption cross-section and (3) tunabile spectral positions of the absorption and emission bands depending on the chosen host material. The most extensively studied transition metal ions in optical spectroscopy are Cr³⁺ and Mn⁴⁺ ions, which seems promising for many applications related to their red or infrared emission [1,2]. However, their properties have already been determined in many host materials, making it possible to roughly predict their behavior in others and thus assume certain limitations. This issue does not apply to Ti³⁺ ions, the stabilization of which beyond the well-known sapphire has only been confirmed in a few host materials. Meanwhile, it has already been presented that the emission and excited state lifetimes of Ti³⁺ ions are characterized by a significant dependence on temperature changes, which may be beneficial for luminescent thermometry [3]. Moreover, Ti³⁺ ions can be characterized by relatively long excited state lifetimes of the order of several tens of milliseconds. Therefore, step-by-step optimization of the synthesis condition and dopant concentration of LaAlO₃ doped with Ti³⁺ ions will be presented in order to understand the influence of dopant concentration on spectroscopic properties and the thermal quenching process. Finally, the influence of non-stoichiometric ion distribution on the above properties will be analyzed.

Acknowledgments:

This work was supported by the National Science Center Poland (NCN) under project no. 2022/45/N/ST5/01457.

References:

[1] W. E. Cohen et al., ECS J. Solid State Sci. Technol. 12, (2023), 76004.

[2] Z. Pan et al., Nat. Mater. 11 (2012) 58–63.

[3] W. M. Piotrowski et al., Chem. Eng. J. 428, (2022), 131165.

Introduction: The opto-electronic characteristics of Zr-doped HfO₂ have been thoroughly investigated by many researchers, yet further research is needed to fully understand these materials. To improve the electrical and optical characteristics of Zr-doped HfO₂ films, experiments involving novel structures are crucial. The analysis of various characteristics of Zr_?Hf_1−?O₂/Al/Zr_?Hf_1−?O₂ trilayer thin-films are still under consideration.

Methods: In this study, Zr_?Hf_1−?O₂/Al/Zr_?Hf_1−?O₂ trilayer thin-films have been deposited with different substrate temperatures varied from 25 to 300^◦C using magnetron sputtering. The trilayer film has been deposited on n type silicon substrates to examine structural and electrical properties. The purpose of depositing the trilayer film on commercial glass substrates is to investigate its optical properties. Zr and HfO₂ targets were co-sputter deposited to form the top and bottom layers of Zr_?Hf_1−?O₂. Using a pure Al target, dc sputtering was used to deposit the intermediate metal layer. Various techniques such as grazing incidence x-ray diffraction, field emission scanning electron microscopy, atomic force microscopy, cross-sectional transmission electron microscopy, and energy-dispersive x-ray spectroscopy were employed for structural analysis. UV–VIS spectroscopy has been employed to investigate optical characteristics of the films. The MOS structure with gate electrodes of 100 μm was fabricated using UV photolithography followed by electron beam evaporation technique. Capacitance–voltage and current–voltage measurements were conducted to evaluate the electrical characteristics of the trilayer thin films.

Results: Physical characterization indicates that increasing the substrate temperature enhances the crystallinity, grain size, and surface roughness of the trilayer thin films. The trilayer thin-film, deposited at 300^◦C, exhibits enhanced optical transmittance across 400 to 1100 nm wavelength. Furthermore, this film exhibits excellent performance in terms of figure of merit, leakage current, and breakdown performance.

Conclusions: These qualities suggest that the films deposited at 300°C hold potential for application in optoelectronic devices.

Thin films with a thickness of a few nanometers to a few tens of nanometers, also called trans-dimensional (TD) materials, are an exceptional tool to tune various opto-plasmonic properties of a system that are unattainable when using both single-layered two-dimensional (2D) counterparts and/or three-dimensional (3D) bulk counterparts. Taking the planned periodic arrangement of single-walled carbon nanotube (SWCNT) films as an example, we semi-analytically calculate the dynamical conductivities and dielectric responses of a TD film as a function of the photon frequency and radius of the SWCNT. The periodic array of SWCNs has an anisotropic dielectric response, which is almost a constant and is the same as that of the host dielectric medium in the perpendicular direction of the alignment of the SWCNT array due to the depolarization effect that SWCNTs have. However, the dielectric response depends on the incident photon energy, in addition to the film’s thickness, the SWCN’s sparseness, inhomogeneity, and the SWCNT’s diameter. The energy difference between the resonant absorption peak and the plasmonic peak varies with the thickness of the film. We reveal that thinner SWCNT TD films have a comparatively stronger exciton-plasmon coupling than thicker SWCNT TD films.

The author gratefully acknowledges the support of the 2024 Ralph E. Powe Junior Faculty Enhancement Awards, provided by Oak Ridge Associated Universities (ORAU).

Photonic technologies have emerged as powerful tools for advancing biochemical sensing and micromanipulation, offering novel approaches in life sciences, diagnostics, and environmental monitoring. In this talk, we will present multidisciplinary work from the Centre of Applied Photonics at INESC TEC, focusing on the development of state-of-the-art photonic platforms. Key innovations in optical fiber sensors, integrated microresonators, and optical tweezers for micromanipulation and sensing will be introduced, with a focus on their specific applications.

Building on these developments, the capabilities of femtosecond (fs) laser microfabrication in creating high-sensitivity monolithic optofluidic platforms will be showcased, with examples such as high-Q resonators coupled with suspended integrated waveguides being introduced. The application of fiber optic technology for high-sensitivity plasmonic sensing of relevant biomolecules will also be explored.

Finally, we will discuss the potential of optical tweezers in extracting valuable information from target bioparticles, demonstrating their utility as a powerful diagnostic tool. These advancements illustrate how photonic technologies continue to push the boundaries of biochemical sensing and micromanipulation, offering exciting possibilities for future research and real-world applications. Ultimately, the integration of these technologies holds the promise of revolutionizing diagnostic capabilities and enhancing our understanding of complex biological systems. By fostering collaboration across disciplines, we can accelerate the development of innovative solutions to pressing global challenges.

Nanomedicine has proven to be a promising avenue for the diagnosis and treatment of various diseases, offering customised solutions that are more specific and effective compared to conventional methods. The main components of nanomedicine are engineered nanoparticles (NPs), which can be produced from a variety of materials. Organic, inorganic, metallic, and polymeric NPs, including dendrimers, micelles, and liposomes, are examples of NPs that are widely explored in nanomedicine. Among them, inorganic NPs offer several advantages, such as tunable size and surface chemistry, high surface-to-volume ratio, chemical stability, biocompatibility, and unique optical, magnetic and electrical properties.

In this work, the use of porous biosilica-based NPs is described for biomedical applications. The NPs are derived from diatomite, a material of sedimentary origin formed from the remains of diatom skeletons. Diatomite-based NPs (DNPs) can be produced in a size range between 100 and 400 nm by a mechanical process based on ultrasound application and filtering. DNPs are characterized by a porous morphology, which is useful for the efficient loading of drugs. Moreover, they can be made photoluminescent for imaging purposes. The biocompatibility and cellular uptake of DNPs are demonstrated using different cancer cell lines, including human epidermoid, breast, cervical, and colorectal cancer cells. The silica surface can be chemically modified by various functionalization strategies to increase the drug uptake capacity of DNPs and improve the pharmacokinetic and pharmacodynamic profiles of the delivered drugs.

A hybrid nanosystem constituted by DNPs covered by gold NPs acting as SERS substrates is proposed for simultaneous intracellular drug sensing and delivery. This nanosystem constitutes the first example of a multifunctional platform realized from diatomite. Active targeting strategies, performed by immobilizing ligands on NPs, are also explored to enhance drug delivery efficiency^.