We report on the reversible photo and thermo modification of optical properties in nanocomposite films of As2S3 nanocrystals and Au nanoparticles dispersed within an acrylic polymer matrix. The films were fabricated by solution blending and spin coating, followed by a 1 h annealing step at 150 degrees C. This thermal treatment induces a pronounced red shift of the absorption edge by 400 meV and broadens the Urbach tail from 0.6 eV to 0.8 eV, indicative of enhanced structural disorder and the formation of metastable As2S3 clusters. Subsequent exposure to 532 nm laser illumination (20 W/cm2) for 1 h fully restores the original absorption spectrum, demonstrating a reversible, light induced annealing effect. Spectroscopic analysis confirms that the Au nanoparticles lower the activation energy of the As2S3 clusters, facilitating the photo thermal switching. These findings reveal a novel mechanism for active control of optical absorption in chalcogenide based nanocomposites and suggest potential applications in switchable photonic devices, optical data storage, and smart coatings.

The circularly polarized photoluminescence (PL) of excitons induced by application of a magnetic field is investigated experimentally and theoretically for an inhomogeneous ensemble of (In,Al)As/AlAs quantum dots with indirect band gap and type-I band alignment. We demonstrate that the circular polarization degree of the PL shows a nonmonotonic dependence on the dot size and the splitting of the oppositely polarized emission bands is significantly larger than the Zeeman splitting of the excitons in individual dots. The low-energy polarized luminescence band has lower intensity than the high-energy one. The polarization sign of the exciton emission coincides in large dots and the wetting layer, while it is opposite in small dots. A model description of this phenomenon that takes into account the equilibrium populations of long-lived exciton states is developed. The dependence of the exciton $g$ factor on the size of the quantum dot is obtained. Good agreement of the modeled spectra with the experimentally observed ones is achieved without any fitting parameters.

This paper presents a study of the photoluminescence and polarized reflectance spectra of WS2 multilayers deposited on Si/SiO2 substrates. We demonstrate that spectral features observed in the 1.9-2.1 eV energy range originate from the dimensional quantization of exciton polaritons within a 0.32 mu m-thick WS2 layer. Key polariton parameters, including resonance frequency, oscillator strength, and exciton damping, are extracted from the data. Furthermore, analysis of the spectral dependence of the reflected light polarization reveals pronounced optical anisotropy in the WS2 multilayers. We identify the presence of a well-defined optical axis, which we attribute to the formation of a moir & eacute; pattern resulting from the stacking and/or relative orientation of the WS2 layers.

Time-resolved and time-integrated circularly polarized photoluminescence of excitons and trions in external magnetic fields up to 10 T has been studied in undoped and n-type doped quantum well structures based on ZnSe. In an undoped structure, a circular polarization of photoluminescence induced by magnetic fields corresponded to the Boltzmann distribution of excitons on Zeeman sublevels. The inverse spin orientation of excitons is observed in doped samples with a carrier density of 3×1010 cm−2 and higher. Model calculations show that the reason for the inverse spin orientation is the effective depletion of the lowest-exciton Zeeman sublevel as a result of the spin-dependent formation of trions. The trion formation time as a result of exciton-electron binding was determined as 2 ps. This is noticeably shorter than the characteristic time of the exciton-photon interaction. The observed effect can be considered as a way of spin manipulation by electric fields.

The spectra of photoluminescence and polarized reflection under normal and oblique incidence of light from structures with quantum wells with symmetric Cd0.9Zn0.1Te/CdTe/Cd0.9Zn0.1Te and asymmetric Cd0.9Zn0.1Te/CdTe/Cd0.4Mg0.6Te barriers have been studied. Due to the mechanical stresses caused by the mismatch of the crystal lattices of the wells and barriers, the energy of light holes in quantum wells was higher than in barriers, i.e., the band structure for them was of type II. However, in the reflection spectra, the lines of heavy and light excitons had comparable intensities. In structures with symmetric barriers, exciton resonances, which do not appear in the photoluminescence spectra, were found in the reflection spectra. A detailed calculation of the energy levels and reflection spectra has been carried out.

In this paper, polarized photoluminescence caused by exciton quasi-equilibrium spin orientation on Zeeman sublevels in an ensemble of quantum dots of different sizes is theoretically studied. It is found that: (i) the splitting of the photoluminescence bands in a magnetic field in an ensemble of quantum dots is several orders of magnitude larger than the Zeeman splitting of exciton levels in a single dot, (ii) the sign of the circular polarization of the photoluminescence changes along the contour of the bands, (iii) the change of the sign of the polarization is associated with the change of the sign of the exciton g-factor. A universal formula for the dependence of the exciton g-factor on the quantum dot size is obtained. This dependence is valid for both bulk material and nanostructures of different types and sizes. Comparison of the results obtained with the experimentally measured data has been carried out.

The spectra of photoluminescence and polarized reflection under normal and oblique incidence of light from structures with quantum wells with symmetric Cd0.9Zn0.1Te/CdTe/Cd0.9Zn0.1Te and asymmetric Cd0.9Zn0.1Te/CdTe/Cd0.4Mg0.6Te barriers have been studied. Due to the mechanical stresses caused by the mismatch of the crystal lattices of the wells and barriers, the energy of light holes in quantum wells was higher than in barriers, i. e., the zone structure for them was of type II. However, in the reflection spectra, the lines of heavy and light excitons had comparable intensities. In structures with symmetric barriers, exciton resonances, which do not appear in the photoluminescence spectra, were found in the reflection spectra. A detailed calculation of the energy levels and reflection spectra has been carried out.

The spectra of polarized reflection from a structure with a single quantum well and asymmetric Cd 0.9 Zn 0.1 Te/CdTe/Cd 0.4 Mg 0.6 Te barriers are studied in this work. The Stokes parameters of reflected light were measured. In the structure with asymmetric barriers under study in the region of exciton resonances, the phenomenon of light birefringence caused by a reduced symmetry of the interfaces compared to the bulk was found.

Photoluminescence and polarized reflection spectra of quantum well structures with symmetric Cd0.9Zn0.1Te/CdTe/Cd0.9Zn0.1Te and asymmetric Cd0.9Zn0.1Te/CdTe/Cd0.4Mg0.6Te barriers were studied. The Stokes parameters of the reflected light from these structures were measured. In structures with asymmetric barriers, in the region of exciton resonances, the phenomenon of light birefringence was detected, caused by a lower symmetry of the interfaces compared with the symmetry of bulk crystals. A discussion of this phenomenon is given.

Photoluminescence and polarized reflection spectra of quantum well structures with symmetric Cd$_{0.9}$Zn$_{0.1}$Te/CdTe/Cd$_{0.9}$Zn$_{0.1}$Te and asymmetric Cd$_{0.9}$Zn$_{0.1}$Te/CdTe/Cd$_{0.4}$Mg$_{0.6}$Te barriers were studied. The Stokes parameters of the reflected light from these structures were measured. In the structures with symmetric barriers, exciton resonances were found in the reflection spectra and were not present in the photoluminescence spectra. In structures with asymmetric barriers, in the region of exciton resonances, the phenomenon of light birefringence was detected, caused by a lower symmetry of the interfaces compared to the symmetry of bulk crystals. A discussion of both phenomena was given.

Unusual optical anisotropy was experimentally observed in hexagonal boron nitride thin films produced from bulk boron nitride via ultrasonication. Both the linear and circular polarisation demonstrated a well-defined single axis of anisotropy over a large sample area. To understand this phenomenon, we employed statistical analysis of optical microscopy images and atomic force microscopy to reveal an ordered particle density distribution at the microscopic level corresponding to the optical axis observed in the polarisation data. The direction of the observed ordering matched the axis of anisotropy. Hence, we attribute the measured optical anisotropy of the thin films to microscopic variations in the particle density distribution.

Тонкие пленки гексагонального нитрида бора толщиной несколько моноатомных слоев были изготовлены путем расщепления объемных образцов в ультразвуковой ванне. Исследовались спектры пропускания, отражения и фотолюминесценции таких пленок. Были измерены спектральные зависимости линейной и круговой поляризации прошедшего через образец света. Исследование с помощью сканирующей электронной микроскопии показало однородность полученных образцов. Однако исследование параметров Стокса прошедшего через образец света позволило установить наличие скрытой анизотропии оптических свойств этих пленок. Ключевые слова: нитрид бора, оптическая анизотропия, спектроскопия, поляризация, тонкие пленки.

Thin hexagonal boron nitride films with a thickness of several monoatomic layers have been manufactured by splitting of bulk samples in an ultrasonic bath. The transmission, reflection, and photoluminescence spectra of such films are studied. The spectral dependences of linear and circular polarization of light passing through the sample are measured. Scanning electron microscopy investigation demonstrates homogeneity of the obtained samples. However, investigation of Stokes parameters of light passing through the sample makes it possible to reveal hidden anisotropy of optical properties of these films.

The spectra of exciton-polariton photoluminescence from cylindrical microcavities under optical excitation below and above the threshold of transition to the polariton laser regime under conditions of strong exciton-photon coupling were studied. At relatively weak optical excitation, lateral quantization modes of polaritons and whispering gallery modes appeared. Both the spectral distribution of these modes and the spatial dependence of their wave functions in the resonator plane were observed. With an increase in the excitation intensity and a transition to the polariton laser regime, only one, the longest-wavelength lasing line remained in the spectrum. It has been suggested that under strong optical excitation, the spectrum contains not only exciton-polariton radiation, but also trion-polariton radiation.

Polariton photoluminescence from cylindrical microcavities was studied under optical excitation below and above a nonlinear regime threshold. Lines of lateral excitonic polaritons quantization were observed in the spectra. In addition to quantization lines with a small orbital quantum number m, exciton-polariton whispering gallery modes with large m > 10 were observed in the cavities of relatively large diameter. In addition to the spectral distribution of the polariton size quantized modes, it was possible to observe their wavefunctions' spatial distribution.

The spectra of exciton-polariton photoluminescence from cylindrical microcavities under optical excitation below and above the polariton lasing threshold under conditions of strong exciton–photon coupling are studied. Under relatively weak optical excitation, modes of lateral quantization of polaritons and whispering gallery modes were detected. Spectral distribution of these modes and spatial dependence of their wave functions in the plane of the cavity were observed. With an increase in the excitation intensity and a transition to the polariton lasing mode, only one, the longest-wavelength lasing line remained in the spectrum. It is suggested that, under strong optical excitation, the spectrum contains not only exciton-polariton, but also trion-polariton radiation.

Heterostructures with atomically thin double quantum wells based on CdTe/ZnTe are investigated by optical spectroscopy (photoluminescence and reflectivity methods) as a function of temperature and density of excitation. Heavy and light exciton luminescence lines are observed with comparable intensities and different temperature behaviors (they cross each other at about 65° K). All these features agree with a complete calculation that takes into account both a very small chemical band offset for such monolayer CdTe inclusions in the ZnTe matrix (namely, 2%), and, consequently, the importance of Coulombic interaction in these double quantum wells.

Abstract Heterostructures of the CdTe/ZnTe type with ultrathin quantum wells are studied. Lines of light and heavy excitons bound to the CdTe layers are observed in the spectra. It is found that the photoluminescence intensity of the light exciton is comparable to the luminescence intensity of the heavy exciton. The temperature shifts of these lines are different, and the lines are intersected at a temperature of 65 K. The estimates of the energy and wave functions of the exciton states have made it possible to clarify parameters of some bands and excitons in such structures.

Reflectivity and modulated photoreflectivity spectra of ZnO and Zn1 – xMgxO epitaxial layers as well as ZnO/Zn1 – xMgxO quantum wells have been studied at normal and oblique light incidence. Comparison of experimental and calculated spectra allowed refinement of certain parameters of excitons in these structures and the order of energy bands in ZnO.

Исследованы спектры отражения и модуляционного фотоотражения от эпитаксиальных слоев ZnO и Zn1-xMgxO, а также квантовых ям ZnO/Zn1-xMgxO при нормальном и наклонном падении света. Сравнение экспериментально измеренных и расчетных спектров позволило уточнить некоторые параметры экситонов в этих структурах и уточнить порядок следования энергетических зон в ZnO. Ключевые слова: гетероструктуры, квантовые ямы, экситоны, спектроскопия.