All-Optical Switching Demonstrated with Photoactive Yellow Protein Films

Integrated optics (IO) is a field of photonics which focuses on manufacturing circuits similar to those in integrated electronics, but that work on an optical basis to establish means of faster data transfer and processing. Currently, the biggest task in IO is finding or manufacturing materials with the proper nonlinear optical characteristics to implement as active components in IO circuits. Using biological materials in IO has recently been proposed, the first material to be investigated for this purpose being the protein bacteriorhodopsin; however, since then, other proteins have also been considered, such as the photoactive yellow protein (PYP). In our current work, we directly demonstrate the all-optical switching capabilities of PYP films combined with an IO Mach–Zehnder interferometer (MZI) for the first time. By exploiting photoreactions in the reaction cycle of PYP, we also show how a combination of exciting light beams can introduce an extra degree of freedom to control the operation of the device. Based on our results, we discuss how the special advantages of PYP can be utilized in future IO applications.

Size- and Temperature-control Optical Direct/indirect Band Tuning in Layered Compounds: Band Gap Engineering

The X-ray diffraction (XRD) is studied in thermally evaporated cadmium iodide (CdI2) thin films with various thicknesses. The grain size, calculated from the XRD, is found to increase with increasing the thickness of the film, while the reflectivity and refractive index decease with increasing the wavelength of the exciting light. The optical absorption spectra show both allowed direct and indirect interband transitions across a fundamental gap in CdI2. It is found that both indirect and direct band gap (Eg) decrease with increasing the thickness of the film and that the indirect Eg is lower than the direct Eg by an amount of about 0.7 eV. The direct Eg is also decreased with increasing both the grain size and temperature. However, the temperature dependence of Eg follows the Varshni relation. Our results highlight the possibility of engineering or tuning the Eg of CdI2 by controlling the thickness of the film, grain size as well as temperature.

Effect of Plasmonic Nanostructures on the Optical Properties of CH3NH3PbI Perovskite Films

This paper investigated the optical properties of both silver island films (SIF) and CH3NH3PbI3 perovskite films obtained on the surface of SIF. It was found that the surface morphology of SIF has a substantial effect on the optical density of perovskite films. Furthermore, a significant redshift in the absorption spectrum of the island films was observed when perovskite is deposited on them. The intensity and lifetime of the luminescence of perovskite films on the surface of the island films depend on the wavelength of the exciting light. The results indicate that SIFs not only can be potentially used to increase the intensity of light emitting diodes based on perovskites, but also prolong the lifetime of charge carriers in perovskites, and thus lead to potentially improve the photovoltaic properties of perovskite solar cells.

Investigations of Electron-Electron and Interlayer Electron-Phonon Coupling in van der Waals hBN/WSe2/hBN Heterostructures by Photoluminescence Excitation Experiments

Monolayers of transition metal dichalcogenides (TMDs) with their unique physical properties are very promising for future applications in novel electronic devices. In TMDs monolayers, strong and opposite spin splittings of the energy gaps at the K points allow for exciting carriers with various combinations of valley and spin indices using circularly polarized light, which can further be used in spintronics and valleytronics. The physical properties of van der Waals heterostructures composed of TMDs monolayers and hexagonal boron nitride (hBN) layers significantly depend on different kinds of interactions. Here, we report on observing both a strong increase in the emission intensity as well as a preservation of the helicity of the excitation light in the emission from hBN/WSe2/hBN heterostructures related to interlayer electron-phonon coupling. In combined low-temperature (T = 7 K) reflectivity contrast and photoluminescence excitation experiments, we find that the increase in the emission intensity is attributed to a double resonance, where the laser excitation and the combined Raman mode A′1 (WSe2) + ZO (hBN) are in resonance with the excited (2s) and ground (1s) states of the A exciton in a WSe2 monolayer. In reference to the 2s state, our interpretation is in contrast with previous reports, in which this state has been attributed to the hybrid exciton state existing only in the hBN-encapsulated WSe2 monolayer. Moreover, we observe that the electron-phonon coupling also enhances the helicity preservation of the exciting light in the emission of all observed excitonic complexes. The highest helicity preservation of more than 60% is obtained in the emission of the neutral biexciton and negatively charged exciton (trion) in its triplet state. Additionally, to the best of our knowledge, the strongly intensified emission of the neutral biexciton XX0 at double resonance condition is observed for the first time.

Особенности спектральных характеристик различных структурных модификаций Lu-=SUB=-1-x-=/SUB=-RE-=SUB=-x-=/SUB=-BO-=SUB=-3-=/SUB=-

The structure, IR absorption and luminescence spectra of the microcrystals of Lu1-xEuxBO3, Lu0.99-xTbxEu0.01BO3, and Lu0.99−xYxEu0.01BO3 orthoborates (0 ≤ x ≤ 0.25) synthesized at 970°С were studied. An increase in х leads to a sequential change of the structural state of the orthoborates. At х ≤ 0.07 – 0.09, the compounds form a solid solution with the calcite structure and microcrystal size of 8 – 20 µm. Then, they become two-phase: the vaterite phase arises along with the calcite structure. At х ≥ 0.2 – 0.25, the entire bulk of a sample has the vaterite structure. A correspondence between the structure and spectral characteristics of these compounds was established. Luminescence spectra were investigated at different wavelengths of exciting light. This allowed obtaining information on the structure of a near-surface layer and the bulk of microcrystals of the investigated samples. It is shown that the vaterite phase arises both in the bulk of large microsrystals (8 – 20 µm) and in the form of small microsrystals (1 – 2 µm).

Одноэлектронный эмиссионно-инжекционный транспорт в микроструктуре с коллоидными квантовыми точками узкозонных полупроводников

By approximating the tunneling current-voltage characteristics (CVCs) of colloidal quantum dots (QDs) of narrow-gap semiconductors InSb and PbS, it is shown that in the one-electron mode, electron transport is determined by competing processes – emission from a quantum dot, injection into it and transport through it with current limitation by space charge. At voltages above 0.5 V, for single QD on the CVCs, regions of instability and current dip similar to the Coulomb gap were observed. Qualitative and numerical comparative estimates suggest that one-electron transport and current limitation similar to the Coulomb blockade are observed in the structure of a segregated set of quantum dots. Illumination of the sample with white light when measuring the CVCs breaks the Coulomb blockade, greatly increasing or decreasing the current, depending on the spectrum of the exciting light.

Эволюция спектральных и структурных характеристик ортоборатов La-=SUB=-0.98-x-=/SUB=-Lu-=SUB=-x-=/SUB=-Eu-=SUB=-0.02-=/SUB=-BO-=SUB=-3-=/SUB=-

The structure, IR absorption, luminescence, and luminescence excitation spectra of La0.98xLuxEu0.02 BO3 orthoborates synthesized at 970°C were studied at 0 ≤ x ≤ 0.98. An increase in х leads to a sequential change of the structural state of the orthoborates. At first, the compound has the aragonite structure. Then, it becomes two-phase and contains the aragonite and vaterite phases. With a further increase in х, the compounds have the vaterite structure, then the vaterite and calcite structure, and, finally, the calcite structure. Correspondence between the structure and spectral characteristics of these compounds was established. Luminescence spectra were investigated at different wavelengths of exciting light. This allowed obtaining information on the structure of a near-surface layer and the bulk of microcrystals of the investigated samples. It is shown that the vaterite phase arises in the bulk of microcrystals of samples that have the aragonite structure.

SOL-GEL PROCESSED SIO2-AL2O3 XEROGELS: SYNTHESIS AND LUMINESCENT PROPERTIES

SiO2-Al2O3 xerogels with various Si : Al ratios were synthesized via sol-gel method (two kinds of synthetic procedures were used) and characterized by means of elemental analysis, XRD, thermogravimetry and IR spectroscopy. No losses of precursors were found during the synthesis and the introduced components are quantitatively transferred from the initial mixture to the composition of the formed samples.The position of the luminescence band in the 300–500 nm region depends on the wavelength of the exciting light, time of gel maturation and the drying temperature, which is the manifestation of the influence of the structure of units in xerogels on the luminescent properties.

A miniaturized fluorescence imaging device for rapid early skin cancer detection

Fluorescence imaging is very useful for skin cancer lesions detection because of its properties of noninvasion and fast imaging. However, conventional fluorescence imaging devices’ excitation light source and camera are usually separated, which will cause problems such as complicated structure, large volume, and poor illumination homogeneity. In this paper, we introduce a miniature portable fluorescence imaging device to diagnose skin cancer. A coaxial design has been introduced to combine the exciting light source and fluorescence receiver as an integral part, which significantly reduces the size of the device and ensures illumination homogeneity. The volume of the device is less than [Formula: see text][Formula: see text]cm3 with weight of 150[Formula: see text]g, and the total power (including the excitation lamp) is only 1.5 W. It is used to detect the squamous cell carcinoma mice for demonstration. The results show that the location of the cancer lesions can be easily distinguished from the images captured by the device. It can be efficiently used to detect early skin tumors with noninvasion. It also has prospects to be integrated with other diagnostic methods such as ultrasound probe, for multiple diagnose of skin tumors thanks to its miniature size.

Quartz-Enhanced Photoacoustic Detection of Ethane in the Near-IR Exploiting a Highly Performant Spectrophone

In this paper the performances of two spectrophones for quartz-enhanced photoacoustic spectroscopy (QEPAS)-based ethane gas sensing were tested and compared. Each spectrophone contains a quartz tuning fork (QTF) acoustically coupled with a pair of micro-resonator tubes and having a fundamental mode resonance frequency of 32.7 kHz (standard QTF) and 12.4 kHz (custom QTF), respectively. The spectrophones were implemented into a QEPAS acoustic detection module (ADM) together with a preamplifier having a gain bandwidth optimized for the respective QTF resonance frequency. Each ADM was tested for ethane QEPAS sensing, employing a custom pigtailed laser diode emitting at ~1684 nm as the exciting light source. By flowing 1% ethane at atmospheric pressure, a signal-to-noise ratio of 453.2 was measured by implementing the 12.4 kHz QTF-based ADM, ~3.3 times greater than the value obtained using a standard QTF. The minimum ethane concentration detectable using a 100 ms lock-in integration time achieving the 12.4 kHz custom QTF was 22 ppm.