In this manuscript, we present a study on the optical properties of ZnO NWs and microcrystals synthesized via hydrothermal method. The NWs were characterized by low-temperature photoluminescence spectroscopy, which revealed resonance modes indicating random lasing behavior mediated by scattering from misoriented nanowires. The spectral position of the resonance modes suggests lasing in the P-band region of exciton–exciton interaction. Our results also indicate a correlation between the surface density of nanostructures and the peak emission intensity. In addition, optically behavior of individual ZnO microprisms integrated in with a thin perovskite active layer were investigated by room-temperature microphotoluminescence spectroscopy. The results indicate that the ZnO microprisms are efficient optical cavities. Overall, our findings demonstrate the potential of hydrothermal synthesis for the fabrication of efficient ZnO-based light-emitting devices.

Zinc oxide (ZnO) nanostructures are widely used in various fields of science and technology due to their properties and ease of fabrication. To achieve the desired characteristics for subsequent device application, it is necessary to develop growth methods allowing for control over the nanostructures’ morphology and crystallinity governing their optical and electronic properties. In this work, we grow ZnO nanostructures via hydrothermal synthesis using surfactants that significantly affect the growth kinetics. Nanostructures with geometry from nanowires to hexapods are obtained and studied with photoluminescence (PL) spectroscopy. Analysis of the photoluminescence spectra demonstrates pronounced exciton on a neutral donor UV emission in all of the samples. Changing the growth medium chemical composition affects the emission characteristics sufficiently. Apart the UV emission, nanostructures synthesized without the surfactants demonstrate deep-level emission in the visible range with a peak near 620 nm. Structures synthesized with the use of sodium citrate exhibit emission peak near 520 nm, and those with polyethylenimine do not exhibit the deep-level emission. Thus, we demonstrate the correlation between the hydrothermal growth conditions and the obtained ZnO nanostructures’ optical properties, opening up new possibilities for their precise control and application in nanophotonics, UV–Vis and white light sources.

Climate change is one of the most important global problems of the 21st century. The territory of Russia is located in an area of significant observed and forecasted climate change. Achieving Russia's carbon neutrality by 2060 requires the development of a national system for monitoring greenhouse gas emissions and uptake. To achieve this goal, the Ministry of Science and Higher Education launched a pilot programme to create a national network of carbon polygons. St Petersburg State University together with Voeikov Main Geophysical Observatory created the concept of Ladoga carbon polygon focusing the study the greenhouse gas absorption (or sequestration) potential of forest ecosystems typical for Northwest Russia. The evolution of this project assumes the establishment of a forest carbon farm (nature-based solutions). Based on the assumption that the territories of forest areas that were previously part of the state agricultural lands of the Leningrad region can be used for carbon farms (afforestation, enhanced carbon uptake by changing land use), an estimate of CO2 absorption has been made. For the total area of forest carbon farms of 677.9 · 103 ha, it was evaluated of 3700 ± 1900 kt CO2/year or (1000 ± 520) ·106kg С/ year. It is shown that the CO2 absorption of such carbon farms can offset up to 20 % of the total CO2 emission of the Leningrad Region and not more than 8 % of the total CO2 emission for the combined region consisting of Leningrad Region and St Petersburg. The economic effect of the operation of forest carbon farms can only be achieved in the long term. At the current price level per tonne of CO2 (35 USD/(t CO2 )), a 1 hectare of forest carbon farm would yield an income of 9500 USD over a 75-year lifetime. This determines the economic feasibility of creating carbon farms, which is also due to the potential for the production of carbon units based on them, which will either be traded on carbon exchanges or be taken into account as the results of activities aimed at reducing carbon emissions.

A model is proposed for the radial growth of III-V nanowires (NWs) in vapor phase epitaxy on masked substrates, which provides explicitly the NW radius as a function of its length. Analytical solutions are obtained for the NW radius in different stages of growth. A comparison of the model with the data on the growth kinetics of GaAs NWs is presented and a good correlation with the data is demonstrated

A model for III-V nanowire (NW) growth in molecular beam epitaxy (MBE) is developed, which describes the NW growth by surface diffusion of adatoms influenced by the shadowing effect. It is shown that the shadowing effect strongly influences the growth kinetics in dense ensembles of NWs. A new solution for the NW length as a function of its radius and deposition thickness is obtained. A comparison is given for theoretical and experimental lengths of InP NWs grown on either adsorbing or reflecting substrates. Keywords: nanowires, adatom diffusion, shadowing effect.

A model for III-V nanowire (NW) growth in molecular beam epitaxy (MBE) is developed which describes the NW growth by surface diffusion of adatoms influenced by the shadowing effect. It is shown that the shadowing effect strongly influences the growth kinetics in dense ensembles of NWs. A new solution for the NW length as a function of its radius and deposition thickness is obtained. A comparison is given for theoretical and experimental lengths of InP NWs grown on either adsorbing or reflecting substrates.

Characteristics of a compact III–V optocoupler heterogeneously integrated on a silicon substrate and formed by a 31 µm in diameter microdisk (MD) laser with a closely-spaced 50 µm × 200 µm waveguide photodetector are presented. Both optoelectronic devices were fabricated from the epitaxial heterostroctructures with InGaAs/GaAs quantum well-dot layers. The measured dark current density of the photodetector was as low as 2.1 µA cm−2. The maximum link efficiency determined as the ratio of the photodiode photocurrent increment to the increment of the microlaser bias current was 1%–1.4%. The developed heterogeneous integration of III–V devices to silicon boards by Au-Au thermocompression bonding is useful for avoiding the difficulties associated with III–V epitaxial growth on Si and facilitates integration of several devices with different active layers and waveguides. The application of MD lasers with their lateral light output is promising for simplifying requirements for optical loss at III–V/Si interface.

The optical properties of Cu2O nanowhiskers grown by the liquid method with material deposition in an electric field have been studied. The spectral lines forbidden by the selection rules for perfect Cu2O crystals were found in the Raman spectra. The nature of related phonon states is analyzed. In the photoluminescence spectra in the red and near-IR regions, broad bands of defective origin are observed. It was found that the presence of a band at 650 nm (1.9 eV) is a specific feature of the photoluminescence of nanowhiskers. Its properties are studied and possible radiation mechanisms are discussed. In the intrinsic absorption region of nanowhiskers, the photoluminescence band at 572 nm (2.17 eV) associated with band-band transitions is detected. At a low excitation level, the emission of a free exciton n = 1 of the yellow exciton series is observed with simultaneous emission of an optical phonon.

The results of experimental studies on the synthesis by molecular-beam epitaxy of AlGaAs nanowires with InGaAs quantum dots are presented. It was shown that, as in the case of the InP/InAsP material system, the formation of predominantly two objects is observed in the body of AlGaAs nanowire: InGaAs quantum dot due to axial growth and InGaAs quantum well due to radial growth. It is important to note that the grown nanostructures were formed predominantly in the wurtzite crystallographic phase. The results of the grown nanostructures physical properties studies indicate that they are promising for moving single-photon sources to the long-wavelength region. The proposed technology opens up new possibilities for integration direct-gap III-V materials with a silicon platform for various applications in photonics and quantum communications. Keywords: semiconductors, nanowires, quantum dots, III-V compounds, silicon, molecular-beam epitaxy.

A model is proposed for the radial growth of III-V nanowires (NWs) in vapor phase epitaxy on masked substrates, which provides explicitly the NW radius as a function of its length. Analytical solutions are obtained for the NW radius in different stages of growth. A comparison of the model with the data on the growth kinetics of GaAs NWs is presented and a good correlation with the data is demonstrated. Keywords: III-V nanowires, radial growth, vapor phase epitaxy, modeling.

Lead halide perovskite nanoplatelets (NPls) attract significant attention due to their exceptional and tunable optical properties. Doping is a versatile strategy for modifying and improving the optical properties of colloidal nanostructures. However, the protocols for B-site doping have been rarely reported for 2D perovskite NPls. In this work, we investigated the post-synthetic treatment of CsPbBr3 NPls with different Cd2+ sources. We show that the interplay between Cd2+ precursor, NPl concentrations, and ligands determines the kinetics of the doping process. Optimization of the treatment allows for the boosting of linear and nonlinear optical properties of CsPbBr3 NPls via doping or/and surface passivation. At a moderate doping level, both the photoluminescence quantum yield and two-photon absorption cross section increase dramatically. The developed protocols of post-synthetic treatment with Cd2+ facilitate further utilization of perovskite NPls in nonlinear optics, photonics, and lightning.

Growth of hexagonal Ge stripes on the side facets of wurtzite AlGaAs and GaAs nanowires is considered. It is shown experimentally and explained within a model that Ge forms stripes on AlGaAs nanowires, while it covers conformally GaAs nanowires. The effect is explained by different surface and interface energies in the two material systems.

The results of experimental studies on the synthesis by molecular-beam epitaxy of AlGaAs nanowires with InGaAs quantum dots are presented. It was shown that, as in the case of the InP/InAsP material system, the formation of predominantly two objects is observed in the body of AlGaAs nanowire: InGaAs quantum dot due to axial growth and InGaAs quantum well due to radial growth. It is important to note that the grown nanostructures were formed predominantly in the wurtzite crystallographic phase. The results of the grown nanostructures physical properties studies indicate that they are promising for moving single-photon sources to the long-wavelength region. The proposed technology opens up new possibilities for integration direct-gap III−V materials with a silicon platform for various applications in photonics and quantum communications.

The optical properties of Cu2O nanowhiskers grown by the liquid method with material deposition in an electric field have been studied. The spectral lines forbidden by the selection rules for perfect Cu2O crystals were found in the Raman spectra. The nature of related phonon states is analyzed. In the photoluminescence spectra in the red and near-IR regions, broad bands of defective origin are observed. It was found that the presence of a band at 650 nm (1.9 eV) is a specific feature of the photoluminescence of nanowhiskers. Its properties are studied and possible radiation mechanisms are discussed. In the intrinsic absorption region of nanowhiskers, the photoluminescence band at 572 nm (2.17 eV) associated with band−band transitions is detected. At a low excitation level, the emission of a free exciton n = 1 of the yellow exciton series is observed with simultaneous emission of an optical phonon.

The small-signal amplitude modulation, threshold, and spectral characteristics of microdisk lasers with InGaAs/GaAs quantum well-dots active region were studied jointly with the spectral and threshold parameters of edge-emitting lasers made from the same epitaxial heterostructure. Using the obtained material parameters, the relative intensity noise of the microdisk lasers was calculated as a function of the bias current and side-mode suppression ratio. It is shown that the integral noise is low enough for error-free optical data transmission with the maximum possible bitrate limited by the microdisk modulation bandwidth, if the bias current is above 1.7× threshold current (for side mode suppression ratio > 20 dB).

Obtaining hexagonal Ge is a great challenge and has previously been achieved by transferring the wurtzite phase of GaAs nanowires, where Ge forms a conformal shell around a nanowire. Here, we demonstrate hexagonal Ge stripes of 6 nm height and 17 nm width, which decorate 25 nm-wide side facets of wurtzite AlGaAs nanowires. Ge shells are grown by molecular beam epitaxy at a low temperature of 320 degrees C. The hexagonal structure of Ge is revealed by Raman spectroscopy and high-resolution transmission electron microscopy (TEM), the latter shows the pure 2H phase. The formation of Ge stripes on the side facets of AlGaAs nanowires is demonstrated by scanning TEM in the angular annular dark-field mode and explained within an energetic model. These results show a possibility of forming 2H wire-like Ge structures with tunable geometry using AlGaAs nanowire templates. Such structures can be exploited for direct band gap engineering and quantum confinement effects and used in near-infrared optoelectronics based on nanostructured Ge.

Experimental data on the rapid (≈4.4 nm s−1) axial growth rate of narrow (≈9 nm in radius) InAs nanowires (NWs) obtained by Au‐catalyzed molecular beam epitaxy on Si substrates at a low surface temperature of 270 °C are presented. These NWs exhibit pure wurtzite crystal structure and an unusually high ratio of the average NW length over the effective thickness of deposited InAs of about 60 despite the presence of parasitic InAs islands on the Si substrate. These trends are explained within a dedicated growth model. In the absence of In evaporation, In atoms either diffuse from the substrate to the NW tips or remain in the parasitic layer. This leads to a linear time dependence of the NW length and other unusual growth properties that are thought to have not previously been accessed.

The absorption spectrum of cadmium selenide nanocrystals in a glassy fluorophosphate matrix has been investigated in the vicinity of the fundamental absorption edge 400–650 nm. The revealed oscillations of the absorption have been interpreted as a manifestation of the quantum-well effect for electrons and holes under strong and intermediate confinement conditions. The data obtained have demonstrated that the individual discrete confinement states arise from the band and exciton states of the bulk crystal. The results are in good agreement with those obtained from theoretical consideration of the intermediate confinement model.

The Raman spectra of nine samples of glasses with different content of CdSe semiconductor nanocrystals of different dimensions obtained by annealing samples are studied. It is established that, in the spectra of nanocrystals of all samples, there appears a line of the fundamental polar vibration whose frequency is close to that of the longitudinal optical mode of the CdSe bulk crystal. In this case, the asymmetry of this line essentially depends on the sample, the semiconductor concentration, and the local excitation place. To analyze the obtained results, a factor analysis method is used to separate linearly independent components from the data set. It is established that three or four contributions with frequencies near 180, 190, 208, and, probably, 210 cm−1 can be singled out in the contour of the line under consideration. A comparison of the obtained results with the conclusions made by using microscopic models demonstrates a significant difference between the experimental data and the results obtained by using mechanical and dielectrical continuum models. It is possible that the real picture of quantum dot vibrations is more complicated and can be described better within the microscopic model. Moreover, for a CdS nanocrystal, the experimental spectra agree satisfactorily with results of calculation of vibrations, in which 3–4 bands with a frequency difference of 10-15 cm−1 exist in the region of the LO mode for crystals with dimensions of 5 × 5 × 5 unit cells (1000 atoms).