Antibiotic resistance is a global health crisis driven by the overuse and misuse of antibiotics. To combat this, effective disinfection of air, water, and surfaces is crucial. Ultraviolet C (UVC) lamps, emitting 220-280 nm radiation, have been used for this purpose since the 1930s. Since UVC radiation does not naturally reach the Earth's surface, microbes have not developed resistance to it.

In this work, we synthesized UVC-emitting phosphor doped with Pr³⁺ ions via a high-temperature solid-state reaction. Praseodymium ions are highly effective for UV luminescence due to their interconfigurational transitions between the 5d and 4f levels. Upon Stokes excitation, we observed broad-band emission in the 230–350 nm range, corresponding to the 4f5d → ³H_j and ³F_j transitions. Notably, the same results were obtained with visible (444 nm) excitation. This upconversion (UC) of visible light into UVC can occur through two mechanisms: energy transfer upconversion (ETU) and excited-state absorption (ESA). We analyzed UC luminescence's dependence on the pumping power and Pr³⁺ concentration, as well as the decay kinetics of upconverted light, and found that both mechanisms can occur with varying effectiveness.

The upconversion properties of the prepared materials make them attractive candidates for mercury-free UVC devices, where high-energy photons can be generated by excitation with low-energy radiation. Additionally, these materials have the potential for use in self-cleaning surfaces that emit UVC radiation when exposed to sunlight [2].

This work was supported by The National Science Centre (NCN) under the OPUS 21 project, grant no. UMO-2021/41/B/ST5/03792, which is gratefully acknowledged.

References

[1] Reed, N.G. The History of Ultraviolet Germicidal Irradiation for Air Disinfection. Public Health Reports 2010, 125, 15–27.

[3] Cates, E.L.; Cho, M.; Kim, J.-H. Converting Visible Light into UVC: Microbial Inactivation by Pr ³⁺ -Activated Upconversion Materials. Environ Sci Technol 2011, 45, 3680–3686.

In coherent diffraction imaging systems, autofocusing technology is used to precisely detect the distance from the detector plane to the sample plane, which is a critical factor affecting imaging resolution and quality. We propose a new clarity evaluation function (CEF) based on amplitude differences of fractional Fourier transform (ADFrFT), which focuses on issues of commonly used CEFs such as poor adaptability to the environment and samples, poor noise robustness, and significant oscillations. ADFrFT is based on the fractional-domain features of the sample as the autofocusing criterion and adds a new parameter for adjusting the ratio of fusion between the spatial and frequency domains. This parameter can take the sample type and detection scenario as prior knowledge and can be flexibly selected according to actual situations. Compared with various qualitative and quantitative CEFs, it relaxes the requirements of sample and scenario types, while guaranteeing accuracy, and the features of the autofocus curves can switch between spatial and frequency domain types. We also propose an autofocus strategy that first searches for the initial range of the focal length and then subdivides the search to optimize in the right direction, which can be achieved only using ADFrFT to obtain autofocus curves of two different characteristics. We demonstrate the effectiveness, flexibility, and versatility of ADFrFT through autofocus simulations and experiments. In the coaxial multi-distance coherent diffraction imaging experiment, we achieved a higher imaging quality compared to physical ranging by accurately correcting the diffraction distance through ADFrFT autofocus.

The lighting industry is intensively looking for materials that can generate white light, similar to sunlight. WLED is a new type of semiconductor lighting device, widely used today due to its low cost, long service life, energy efficiency, excellent reliability and environmental friendliness. Commonly used WLED lighting generates light that contains too strong a blue component and no red one, which has a negative impact on health. Our solution is to use Ba₂MgMoO₆ (BMM) as a host for Sm³⁺, as a potential red phosphor to improve the color characteristics of WLEDs.

In this study, the red phosphor of 1% Sm³⁺ ion-doped BMM with a double perovskite structure was prepared using a co-precipitation method. Next, we obtained amorphous structures in the form of balls with a diameter of 1.0 mm, using a unique aerodynamic levitation method. Then, an attempt was made to obtain glass ceramics by crystallising BMM crystallites surrounded by an amorphous structure by heating it at the designated crystallization temperature. The structural and spectroscopic properties of the obtained materials were analyzed.

We can successfully conclude that the obtained BMM:Sm³⁺ materials are good candidates as a red phosphor (CRI=91 and CCT=2943 K), giving a warm white emission. Temperature measurements brought us completely unexpected results. The relative sensitivity calculated from FIR had a maximum of 2.7% K^-1 at -30 ⁰C and another local maximum of 1.6% K^-1 at 75 ⁰C. This value is one of the highest achieved for luminescence thermometry performed only using Sm³⁺ ions. This is an extremely promising precedent for temperature sensing using perovskite materials with high symmetry. Transparent glass samples were obtained (Fig. 1). From the XRD patterns, only a broad diffuse peak is observed, which indicates that the samples are totally amorphous, without any traces of crystalline structure. The SEM images show the homogeneous topography of the sample.

Autofocusing technology is an essential automatic adjustment technology that relies on the clarity evaluation function to achieve clear and accurate imaging in imaging systems. This technology originated from traditional optical microscopes and has been widely promoted in the new generation of microscopic imaging systems, as well as in the more extensive application of computational microscopy imaging technology. Microscopic imaging is closely related to autofocusing technology, from the focusing process of the microscope stage to the calculation of distance parameters in computational imaging technology. Achieving fast and intelligent autofocusing performance in microscopic imaging systems is a pressing research task for the disciplines that apply computer vision automatic detection systems.

In this context, an autofocusing algorithm based on the Tanimoto coefficient was proposed to solve the problems of inaccuracy and low sensitivity of autofocusing results in colour microscopy due to complex colour changes. Background areas without useful information will result in a large amount of computation and affect the accuracy of autofocusing results. The Harris corner detection operator was used to extract the salient feature region as the definition evaluation object. In order to solve the contradiction between ergodic search and high-precision autofocusing in multi-range coherent diffraction imaging, a focusing algorithm based on subdivision search is proposed to accelerate the autofocusing process.

The reconstruction of motion-blurred images and the acquisition of target velocity are widely used in image processing, computer vision and so on. Using traditional optical methods such as Hough transform or differential multiplier, it is difficult to obtain high-resolution and high-definition image quality reconstruction results. Although using deep learning methods for image reconstruction can obtain better results, it will also bring some problems, such as huge data volume, long training time and complex data set construction. In this study, we firstly propose a method based on optimized Radon transform and optical model, combined with adaptive erosion operation, which can process motion-blurred images of various styles and degrees by giving their blur information exactly. Secondly, we construct a sharpness evaluation function scoring algorithm to filter the reconstructed images, which can use blurred information to reconstruct high-fidelity images. Finally, we design a velocity measurement method based on an optical imaging camera system by using blurred prior information. The results show that the blurry image reconstruction and velocity measurement have high robustness and can deal with motion blur in simulations and experiments. The method proposed in this paper can reconstruct a variety of motion-blurred images with high fidelity, and can accurately calculate the motion velocity of the target, which has great application value in the field of image processing, computer vision, and so on.

Gold nanospheroids and cylinders exhibit two surface plasmon resonances, transverse (T mode) and longitudinal (L mode), in the infrared band. In accordance with the dipolar plasmonic response of spheroids, an increase in the aspect ratio (η) causes the two resonances to split further apart spectrally, with the T mode undergoing a blue shift while the L mode moves towards longer wavelengths.
We present in this work a numerical approach to studying the effect of anisotropy on the heating of prolate gold nanoparticles (GNs) interacting with a Ti–Sapphire laser oscillating at a wavelength of 800 nm. The GNs are cooled in water, and the heat transfer from the particles to the water is assumed to occur without mass transfer. The effect of η on the GN temperatures is investigated under 100-femtosecond laser pulse irradiation and 1 J/m2 fluence, and several values of η are considered: 2, 3, 4, and 5. First, the extinction cross-section of randomly oriented GNs was computed in the quasi-static limit using the Rayleigh–Gans formulae. Second, the ultrafast dynamics of the heat inside the GNs and at the GN/water interface were modeled through two temperature equations and Fourier’s law, respectively. The numerical simulation was carried out by a code written in C++ language. It was found that the maximum temperature at the GN/water interface increases as a function of η but does not exceed a certain value corresponding to η= 4.5, and this is independent of the size of the GNs.

Picosecond (ps-) laser systems can be successfully employed in ultrafast micromachining due to some specific characteristics such as extended system stability, reduced costs, increased laser pulse energies, and higher repetition rates. However, there are only a few reports in the literature regarding the fabrication of waveguides in glasses and crystalline materials with laser systems delivering pulses of few ps-pulse duration [1]. In general, such waveguides are realized with femtosecond (fs-) laser sources and by using a line-by-line translation inscription technique along a defined shape [2].

In this work, we are reporting on the fabrication of buried depressed-cladding waveguides in a 0.7-at.% Nd:CLNGG disordered crystal by ps-laser beam writing. The laser emission performances were characterized under the pump at 807 nm with a fiber-coupled diode laser. For a quasi-continuous-wave pumping regime, a waveguide with 100 mm diameter (circular cross-section) delivered laser pulses at 1.06 mm with energy E_p= 0.35 mJ for a pump pulse energy of E_pump= 13.3 mJ (corresponding to an overall optical-to-optical efficiency h_o= 0.03), with a slope efficiency of h_s = 0.04. Such waveguides are good candidates for the realization of integrated laser sources consisting of cladding waveguides pumped by diode lasers and for the generation of ultra-short laser pulses at 1 mm.

Funding: This work was financed by the postdoctoral project PD 63/2022, code PN-III-P1-1.1-PD-2021-0522 and partially supported by the program NUCLEU-LAPLAS VII 30N/2023, Ministry of Research, Innovation and Digitization, Romania. The support of the National Interest Infrastructure facility IOSIN - CETAL at INFLPR is acknowledged.

1. Corbari, C.; Champion, A.; Gecevičius, M.; Beresna, M.; Bellouard, Y; Kazansky, P.G. Femtosecond versus picosecond laser machining of nano-gratings and micro-channels in silica glass. Opt. Express 2013, 21, 3946-3958.
2. Okhrimchuk, A.; Mezentsev, V.; Shestakov, A.; Bennion, I. Low loss depressed cladding waveguide inscribed in YAG:Nd single crystal by femtosecond laser pulses. Opt. Express 2012, 20, 3832-3843.

Direct writing with ultrashort laser pulses is considered to be a very efficient technique for fabricating 3D waveguide structures, such as s-curved waveguides, beam splitters or Y-type waveguides, because it allows for the fabrication of structures with arbitrary geometries in various transparent materials. Among them, Y-branch splitters represent basic elements for the development of integrated photonic devices of interest in various applications, including power dividers, interferometers, multiplexers or micro-fluidic devices.

In this work, we report on the realization of Y-branch beam splitters in 1.1-at.% Nd:YAG ceramics by picosecond-laser beam writing. Laser emission performances were investigated under the pump at 807 nm with fiber-coupled diode lasers. For quasi-continuous-wave pumping, laser emission at 1.06 mm was generated for all waveguides. The linear waveguide (NYAG-Y0; 150 mm width x 100 mm height) yielded laser pulses with an energy of E_p= 2.2 mJ for a pump energy of E_pump= 12.8 mJ at 807 nm (corresponding to an overall optical-to-optical efficiency, η_o, of 0.17); the slope efficiency was η_s= 0.21. The NYAG-Y1 waveguide (1° splitting angle; 75 mm width x 100 mm height) emitted laser pulses with a maximum energy of E_p= 1.32 mJ (η_o= 0.10 and η_s= 0.12). Furthermore, the NYAG-Y2 waveguide (2° splitting angle; 75 mm width x 100 mm height) yielded laser pulses with a lower energy of E_p= 1.20 mJ at an efficiency of η_o= 0.09 and with a slope of η_s= 0.11. The emission performances of these Y-branch waveguide beam splitters confirm that they are promising candidates for realizing the use of integrated devices of interest for various advanced photonics circuits.

Funding: This work was financed by the project PD 63/2022, PN-III-P1-1.1-PD-2021-0522, and partially supported by the program NUCLEU-LAPLAS VII 30N/2023, Ministry of Research, Innovation and Digitization, Romania. The support of the National Interest Infrastructure facility IOSIN - CETAL at INFLPR is acknowledged.

Plasmonic sensors offer ultra-sensitive detection capabilities at the nanoscale, enabling the detection of slight variations in refractive index, molecular binding events, and environmental conditions. Their compact size and compatibility with integrated circuits make them promising candidates for various applications, ranging from biomedical diagnostics to environmental monitoring and beyond. In this study, a comprehensive numerical investigation is conducted using the finite element method (FEM) to analyze a plasmonic sensor employing a metal–insulator–metal (MIM) waveguide for temperature sensing applications. The sensor configuration includes a resonant cavity that is coupled to the MIM bus waveguide and filled with a PDMS polymer. Initially, the device's sensitivity is approximately −0.44 nm/°C. While recognizing the existence of various sensitive plasmonic sensor designs, a gap in understanding the light coupling mechanisms to nanoscale waveguides is identified. To address this, a novel approach is employed: orthogonal mode couplers specifically tailored for plasmonic chips utilizing MIM waveguide-based sensors . Through optimization, the hybrid system, comprising silicon couplers and an MIM waveguide, exhibits optimized transmission ranging from −1.73 dB to −2.93 dB across a broad wavelength spectrum of 1450–1650 nm. The strategic integration of these couplers not only distinguishes the proposed plasmonic sensor but also positions it as a highly promising solution for an extensive range of sensing applications.

Currently, luminescent materials can be found in many important devices, including optical sources, displays, lasers, data storage, dosimeters, high-speed luggage scanners, and CT scanners. In most cases, these are semiconductor materials consisting of a host lattice doped with an activator (transition or rare earth ion). Host matrices doped with rare earth elements and exhibiting luminescence initially caught the attention of scientists in the 1930s. However, more in-depth research into these materials started in the 1960s. In subsequent years, the interest in them has steadily grown due to the development of new applications and the evolving industrial requirements for known materials. One of the extraordinary properties of rare-earth-doped materials that demonstrate luminescence is upconversion emission. There is a strong demand for generating artificial UV light for purposes such as surface decontamination, photopolymerization, solar hydrogen production, and the treatment of skin diseases, including cancer. The current methods of UV generation are costly, inefficient, and harmful to the environment. Therefore, one of the innovative approaches for UV generation is visible-to-ultraviolet upconversion. The Pr³⁺ ion, which predominantly emits in the UVC range (100-280 nm), is the most unique and least-studied activator in this context.

In this study, crystallites of new phosphates doped with varying concentrations of Pr³⁺ were synthesized using the solid-state method. The structure, optical, and upconversion properties in the UV-vis range were examined. Methods for improving the intensity of upconversion emission will be discussed.

ACKNOWLEDGMENTS

This work was supported by the National Science Centre under Grant No. UMO-2021/41/B/ST5/03792, which is gratefully acknowledged. One of the authors, A. Grippa (Oleksandr Gryppa), is thankful to the Polish Academy of Sciences for their support via the PAN-NANU (PAS-NASU) program of scientists cooperating with INTiBS PAN.