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Hybrid polymer films of polyvinyl pyrrolidone (PVP)/polyvinyl alcohol (PVA) embedded with gradient levels of Bi-powder were prepared using a conventional solution casting process. XRD, FTIR, and SEM techniques have been used to examine the micro/molecular structure and morphology of the synthesized flexible films. The intensities of the diffraction peaks and transmission spectrum of the PVP/PVA gradually declined with the introduction of Bi-metal. In addition, filler changes the microstructure surface of the pure film. The modification in the microstructure leads to an enhancement in the optical absorption characteristic of the blend films. The indirect allowed transition energy was calculated via Tauc’s and ASF (Absorption Spectra Fitting) models. The decrease in the hybrid film’s bandgap returns to the localized states in the forbidden region, which led the present films to be suitable for photo-electric, solar cell, etc., applications. The relation between the transition energy and the refractive index was studied. The enhancement in the refractive index with Bi-metal concentrations led to use the as-prepared films in optical sensors. The rise of Bi-metal concentrations leads also to the improvement of the nonlinear susceptibility and refractive parameters. The optical limiting characteristics revealed that the higher concentration dopant films reduce the light transmission intensity which is appropriate for laser attenuation and optical limiting in photonic devices. The results suggest that hybrid films are promising materials in a wide range of opto-electronic applications.

We investigate phonon induced electronic dynamics in the ground and excited states of the negatively charged silicon-vacancy ( ) centre in diamond. Optical transition line widths, transition wavelength and excited state lifetimes are measured for the temperature range 4 K-350 K. The ground state orbital relaxation rates are measured using time-resolved fluorescence techniques. A microscopic model of the thermal broadening in the excited and ground states of the centre is developed. A vibronic process involving single-phonon transitions is found to determine orbital relaxation rates for both the ground and the excited states at cryogenic temperatures. We discuss the implications of our findings for coherence of qubits in the ground states and propose methods to extend coherence times of qubits.

We report the photon number resolution at a telecommunication wavelength using a fabricated iridium optical transition edge sensor (TES). Iridium is a chemically stable material, and hence, the iridium TES is expected to exhibit long-term stable device characteristics. Because of the material stability, iridium TES can be formed in relatively simple single-layer structure, which would exhibit uniform device characteristics if large-arrays are constructed in a future. An iridium TES with a sensitive area of 8 μm × 8 μm was fabricated via radio frequency magnetron sputtering, photolithography, and a lift-off technique. The device was cooled in a dilution refrigerator, and its characteristics such as current-to-voltage curve, power-to-voltage curve, and power-to-bath-temperature curve were investigated. The TES exhibited a transition temperature of 355 mK. The TES was irradiated with a pulsed laser source with a wavelength of 1528 nm. A fast response speed was obtained using the TES, and the dominant decay time constant was 761 ns. The photon number resolution was successfully performed, and the energy resolution was 0.464 eV in full width at half maximum.

Large excitonic binding energies in monolayers of transition metal dichalcogenides such as molybdenum disulfide (MoS 2 ), molybdenum diselenide (MoSe 2 ), tungsten disulfide (WS 2 ) and tungsten diselenide (WSe 2 ), were calculated using a gravitational search algorithm. The optimized fitness function is based on a two dimensional (2D) effective mass model of excitons, parameterized by first principle calculations, including a suitable treatment of screening. In addition to the ground state, the binding energies of the first few excited states of the exciton were computed, hence the optical transition energies, as a function of principal quantum number n, were obtained for the exciton states. The method was also used to predict the corresponding 2D polarizabilities, and consequently, dielectric constants for the 2D semiconductors. Dependence of the effective dielectric constants on n was also investigated. Our results compare favorably with existing theoretical methods based on density function theory or GW approximation and the Bethe–Salpeter equation. Furthermore, our results are in reasonable agreement with recent experimental measurements.

In this paper, we propose a method for resonant optical excitation of ortho states of two-electron donors in silicon, direct transitions to which from the ground state are extremely suppressed in case of a weak spin-orbit coupling. Excitation is proposed to be carried out using the points of anti-crossing of ortho and para states under conditions of uniaxial stress of the crystal. In these points the states cannot be unambiguously assigned to any group of states with a certain spin, as a result of which the optical transition becomes allowed. The structure of the energy levels of two-electron impurities is such that the excitation of such state almost unambiguously leads to the population of the underlying ortho-type state, which is expected to be very long-lived in the case of weak spin-orbit coupling. In the present work, theoretical estimates of the cross sections for optical transitions in the vicinity of the level anticrossing point as a function of strain for strong and weak spin-orbit coupling are made.

Coherent optical transition radiation (COTR) from femtosecond electron bunches is simulated using an earlier proposed model. It is shown that partial screening of the COTR field followed by focusing with a lens allows increasing the spatial resolution and makes it possible to measure transverse bunch sizes accurate within a few microns. It is demonstrated that the most reasonable lens screening ratio equals to 50%. Given this, it is possible to eliminate the ring-like structure typically observed on bunch images as a result of coherence.

The optical properties of alternating ultrathin Ti 0.91 O 2 nanosheets and CdS nanoparticle hybrid spherical structures designed by the layer-by-layer (LBL) assembly technique are investigated. From the photoluminescence (PL) spectral measurements on the hybrid spherical structures, a spectrum-shifted fluorescence emission occurs in this novel hybrid material. The time-resolved PL measurements exhibit a remarkably increased PL lifetime of 3.75 ns compared with only Ti 0.91 O 2 spheres or CdS nanoparticles. The novel results were attributed to the enhanced electron-hole separation due to the new type II indirect optical transition mechanism between Ti 0.91 O 2 and CdS in a charge-separated configuration.

Strong optical absorption by a semiconductor is a highly desirable property for many optoelectronic and photovoltaic applications. The optimal thickness of a semiconductor absorber is primarily determined by its absorption coefficient. To date, this parameter has been considered as a fundamental material property, and efforts to realize thinner photovoltaics have relied on light-trapping structures that add complexity and cost. Here we demonstrate that engineering cation disorder in a ternary chalcogenide semiconductor leads to considerable absorption increase due to enhancement of the optical transition matrix elements. We show that cation-disorder-engineered AgBiS2 colloidal nanocrystals offer an absorption coefficient that is higher than other photovoltaic materials, enabling highly efficient extremely thin absorber photovoltaic devices. We report solution-processed, environmentally friendly, 30-nm-thick solar cells with short-circuit current density of 27 mA cm−2, a power conversion efficiency of 9.17% (8.85% certified) and high stability under ambient conditions.AgBiS2 nanocrystals with enhanced optical absorption yield efficient ultrathin solar cells.

The strong light-matter interaction and the valley selective optical selection rules make monolayer (ML) MoS2 an exciting 2D material for fundamental physics and optoelectronics applications. But, so far, optical transition linewidths even at low temperature are typically as large as a few tens of meV and contain homogeneous and inhomogeneous contributions. This prevented in-depth studies, in contrast to the better-characterized ML materials MoSe2 and WSe2 . In this work, we show that encapsulation of ML MoS2 in hexagonal boron nitride can efficiently suppress the inhomogeneous contribution to the exciton linewidth, as we measure in photoluminescence and reflectivity a FWHM down to 2 meV at T=4K . Narrow optical transition linewidths are also observed in encapsulated WS2 , WSe2 , and MoSe2 MLs. This indicates that surface protection and substrate flatness are key ingredients for obtaining stable, high-quality samples. Among the new possibilities offered by the well-defined optical transitions, we measure the homogeneous broadening induced by the interaction with phonons in temperature-dependent experiments. We uncover new information on spin and valley physics and present the rotation of valley coherence in applied magnetic fields perpendicular to the ML.

Optical tweezers provide a versatile platform for the manipulation and detection of single atoms. Here, we use optical tweezers to demonstrate a set of tools for the microscopic control of atomic strontium, which has two valence electrons. Compared to the single-valence-electron atoms typically used with tweezers, strontium has a more complex internal state structure with a variety of transition wavelengths and linewidths. We report single-atom loading into an array of subwavelength scale optical tweezers and light-shift-free control of a narrow-linewidth optical transition. We use this transition to perform three-dimensional ground-state cooling and to enable high-fidelity nondestructive imaging of single atoms on subwavelength spatial scales. These capabilities, combined with the rich internal structure of strontium, open new possibilities including tweezer-based metrology, new quantum computing architectures, and new paths to low-entropy many-body physics.