Core–shell nanorods (NRs) with InGaN/GaN quantum wells (QWs) are promising for monolithic white light-emitting diodes and multi-color displays. Such applications, however, are still a challenge because intensity of the red band is too weak compared with blue and green. To clarify this problem, we measured photoluminescence of different NRs, depending on power and temperature, as well as with time resolution. These studies have shown that dominant emission bands come from nonpolar and semipolar QWs, while a broad yellow-red band arises mainly from defects in the GaN core. An emission from polar QWs located at the NR tip is indistinguishable against the background of defect-related luminescence. Our calculations of electromagnetic field distribution inside the NRs show a low density of photon states at the tip, which additionally suppresses the radiation of polar QWs. We propose placing polar QWs inside a cylindrical part of the core, where the density of photon states is higher and the well area is much larger. Such a hybrid design, in which the excess of blue radiation from shell QWs is converted to red radiation in core wells, can help solve the urgent problem of red light for many applications of NRs.

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Graphene is considered as a promising candidate for manufacturing of sensors due to its extreme sensitivity to molecule absorption. In this work, we show the connection between the electrical and optical properties of epitaxial graphene chips grown on 4H-SiC and intended for the production of protein-based sensors. Using of a complex of techniques, including Raman spectroscopy, atomic force microscopy, Kelvin probe microscopy, study of I-V characteristics and low-frequency noise, it is shown that the character of frequency dependence of the spectral density of voltage fluctuations and its value at a frequency of 1 Hz can be used for classification and selection of graphene chips for their application as sensors. Classification of the graphene chips will allow more efficient development of graphene-based biosensors.

In this work, we demonstrate the possibility of using mechanical Scanning probe lithography (m-SPL) for fabricating nanophotonic devices based on multilayered transition metal dichalcogenides (TMDCs). By m-SPM, we created a nanophotonic resonator from a 70-nm thick MoSe2 flake transferred on Si/Au substrate. The optical properties of the created structure were investigated by measuring microphotoluminescence. The resonator exhibits four resonance PL peaks shifted in the long-wavelength area from the flake PL peak. Thus, here we demonstrate that m-SPL is a high-precision lithography method suitable for creating nanophotonic devices based on multilayered TMDCs.

The fine structure of the exciton spectrum, containing optically allowed (bright) and forbidden (dark) exciton states, determines the radiation efficiency in nanostructures. We study timeresolved micro-photoluminescence in MoS2 monolayers and bilayers, both unstrained and compressively strained, in a wide temperature range (10-300 K) to distinguish between exciton states optically allowed and forbidden, both in spin and momentum, as well as to estimate their characteristic decay times and contributions to the total radiation intensity. The decay times were found to either increase or decrease with increasing temperature, indicating the lowest bright or lowest dark state, respectively. Our results unambiguously show that, in an unstrained film, the spin-allowed state is the lowest for a series of A excitons (1.9 eV) with the dark state being about 2 meV higher, and that the splitting energy can increase several times at compression. In contrast, in the indirect exciton series in bilayers (1.5 eV), the spinforbidden state is the lowest, being ~ 4 meV below the bright one. The strong effect of strain on the exciton spectrum can explain the large scatter among the published data and must be taken into account to realize the desired optical properties of 2D MoS2.