The characteristics of single photons emitted by columnar microstructures based on epitaxial microcavity heterostructures with distributed Bragg reflectors, which include self-organized InAs/GaAs quantum dots and have a comparatively low Q factor in the range of 2000–3000, have been studied. It has been shown that a state with a given spin configuration—exciton with a certain polarization or trion—can be initialized in a single quantum dot under the coherent resonant linearly polarized optical pumping by a π pulse. The measurement of two-photon interference by the Hong–Ou–Mandel scheme has demonstrated that the degree of indistinguishability of successively emitted single photons is 97 and 93% at a time delay of 2 and 250 ns, respectively. Prospects of application of such sources in optical quantum computing schemes have been discussed.

InSe is a promising material for next-generation two-dimensional electronic and optical devices, the characteristics of which are largely determined by the type of band structure, direct or indirect. In general, atomic force microscopy and optical methods can be sensitive to peculiarities of the electronic structure, leading to different results. In this work we will focus on the luminescent properties of few-layer $\beta$-InSe with a thickness of 6–75 monolayers (MLs). Low-temperature micro-photoluminescence ($\mu$-PL) studies show a sharp increase in PL intensity in the range of thicknesses from 16 to 20 monolayers, where, in addition, there is a singularity in the dependence of the work function on the thickness. Time-resolved photoluminescence spectroscopy reveals three characteristic PL decay times that differ from each other by about an order of magnitude. We associate the processes underlying the two faster decays with the recombination of electrons and holes between the band extrema, either directly or through the interband relaxation of holes. Their contributions to the total PL intensity increase significantly in the same thickness range, 16–20 MLs. On the contrary, the slowest contribution, which we attribute mainly to the defect-assisted recombination, prevails at a smaller number of monolayers and then noticeably decreases. These results indicate the indirect-to-direct band-gap transition near 16–20 MLs, which determines the range of applicability of few-layer $\beta$-InSe for efficient light emitters.

Fluorescence spectra of nanodiamonds synthesized at high pressure from adamantane and other organic compounds show narrow (≈1 nm) lines of unknown origin over the spectroscopic range from ≈500 to 800 nm. The study proposes and experimentally confirms the hypothesis that these lines are related to radiative recombination of donor–acceptor pairs (DAP). According to the experimental data, these pairs can be formed from donor‐like substitutional nitrogen present in the diamond lattice and 2D acceptor layer resulting from the effect of transfer doping on the nanodiamond surface. A peculiar behavior of the narrow lines is identified within the temperature range of 100–10 K: their energy position slightly shifts downward, and the majority of the lines divide into two or more components as the temperature decreases. The lines are shown to be predominantly associated with single photon emitters, with an emission rate exceeding 1 million counts s ⁻¹ at room temperature. A new narrowband source of room‐temperature fluorescence found in hydrogen‐terminated nanodiamonds push horizons for quantum optical technologies related to the development of single photon emitters and temperature nanosensors.

A single nanotube synthesized from a transition metal dichalcogenide (TMDC) exhibits strong exciton resonances and, in addition, can support optical whispering gallery modes. This combination is promising for observing exciton-polaritons without an external cavity. However, traditional energy-momentum-resolved detection methods are unsuitable for this tiny object. Instead, we propose to use split optical modes in a twisted nanotube with the flattened cross-section, where a gradually decreasing gap between the opposite walls leads to a change in mode energy, similar to the effect of the barrier width on the eigenenergies in the double-well potential. Using micro-reflectance spectroscopy, we investigated the rich pattern of polariton branches in single MoS₂ tubes with both variable and constant gaps. Observed Rabi splitting in the 40–60 meV range is comparable to that for a MoS₂ monolayer in a microcavity. Our results, based on the polariton dispersion measurements and polariton dynamics analysis, present a single TMDC nanotube as a perfect polaritonic structure for nanophotonics.

In this paper, we studied the role of the crystal structure in spheroidal CdSe nanocrystals on the band-edge exciton fine structure. Ensembles of zinc blende and wurtzite CdSe nanocrystals are investigated experimentally by two optical techniques: fluorescence line narrowing (FLN) and time-resolved photoluminescence. We argue that the zero-phonon line evaluated by the FLN technique gives the ensemble-averaged energy splitting between the lowest bright and dark exciton states, while the activation energy from the temperature-dependent photoluminescence decay is smaller and corresponds to the energy of an acoustic phonon. The energy splittings between the bright and dark exciton states determined using the FLN technique are found to be the same for zinc blende and wurtzite CdSe nanocrystals. Within the effective mass approximation, we develop a theoretical model considering the following factors: (i) influence of the nanocrystal shape on the bright–dark exciton splitting and the oscillator strength of the bright exciton, and (ii) shape dispersion in the ensemble of the nanocrystals. We show that these two factors result in similar calculated zero-phonon lines in zinc blende and wurtzite CdSe nanocrystals. The account of the nanocrystals shape dispersion allows us to evaluate the linewidth of the zero-phonon line.