Nanoplasmonic Raman detection of bromate in water.

The possibility of using surface enhanced Raman scattering (SERS) detection method for bromate-anion determination and quantitative evaluation in water has been demonstrated for the first time. The decreasing of Rhodamine 6G (R6G) Raman peaks intensity has been used as the analytical signal corresponding to the catalytic oxidation by bromate. Electrostatically immobilized silver nanoparticles have been proven as efficient SERS-active substrate. A linear relationship between the Raman intensity of Rh6G as a function of BrO(3)(-) was observed in the range of 0 - 10(-7) М and the detect limit was as low as 10(-10) M (nearly 0.01 µg/L). The results prove the potential of the proposed method for further application in the development of new portable SERS-based sensors for drinking water monitoring with high sensitivity, simplicity and the low cost.

Hyperbolic metamaterials based on quantum-dot plasmon-resonator nanocomposites.

We theoretically demonstrate that nanocomposites made of colloidal semiconductor quantum dot monolayers placed between metal nanoparticle monolayers can function as multilayer hyperbolic metamaterials. Depending on the thickness of the spacer between the quantum dot and nanoparticle layers, the effective permittivity tensor of the nanocomposite is shown to become indefinite, resulting in increased photonic density of states and strong enhancement of quantum dot luminescence. This explains the results of recent experiments [T. Ozel et al., ACS Nano 5, 1328 (2011)] and confirms that hyperbolic metamaterials are capable of increasing the radiative decay rate of emission centers inside them. The proposed theoretical framework can also be used to design quantum-dot/nanoplasmonic composites with optimized luminescence enhancement.

Photoluminescent Properties of Phosphor Based on Perovskite CsPbBr3 Nanocrystals Combined with Violet Leds.

The characteristics of an LED lighting system consisting of a commercial violet LED and a green phosphor based on CsPbBr3 nanocrystals are studied in the context of development of LED illumination sources with antibacterial effects but without harmful effects on human health. The internal efficiency of the nanocrystalline phosphor in a silicone compound was found to exceed 40%, dropping noticeably because of heating for an electric current of ~0.1 A (phosphor excitation intensity ~0.1 W/mm2). This undesirable feature can be diminished by using a remote phosphor design for the illuminators and by using chemical techniques to improve the thermal stability of the nanocrystals.

Anomalous retroreflection from strongly absorbing nanoporous semiconductors.

Pronounced retroreflection behavior is reported for a fishnet nanoporous strongly absorbing semiconductor material. Retroreflection features a half-cone about 0.35 rad along with diffusive specular reflection for all angles of incidence. Retroreflection is apparent by the naked eye with daylight illumination and exhibits no selectivity with respect to wavelength and polarization of incident light featuring minor depolarization of retroreflected light. The reflectance in the backward direction measures 12% with respect to a white scattering etalon. The phenomenon can be classified neither as coherent backscattering nor as Anderson localization of light. The primary model includes light scattering from strongly absorptive and refractive superwavelength clusters existing within the porous fishnet structure. A reasonable qualitative explanation is based on the fact that strict retroreflection obeys shorter paths inside absorbing medium, whereas all alternative paths will lead to stronger absorption of light.

Surface enhanced Raman scattering of inorganic microcrystalline art pigments for systematic cultural heritage studies.

The present work summarizes our experimental data on Surface-enhanced Raman scattering (SERS) of inorganic pigments. The effect of pigment type on Raman scattering enhancement was studied. The paper also describes the features of the SERS-active substrates used as well as the methods of sample preparation for SERS analysis of the pigments. The results of successful application of SERS and micro-SERS for art pigments identification in the canvas paintings and icons have been demonstrated. The techniques allowed us to clearly identify the composition of blue and green paint layers as well as grounds in the nine artworks. This lead to determination of the lower time limit of work creation, to dating of the restoration interventions, to distinguish red ochers from two different deposit sources of raw mineral. The enhancement of Raman scattering intensities allows to reduce significantly the amount of the sample being taken from artwork (up to 1 µg).

Constraints on transmission, dispersion, and density of states in dielectric multilayers and stepwise potential barriers with an arbitrary layer arrangement.

Normal-incidence transmission and dispersion properties of optical multilayers and one-dimensional stepwise potential barriers in the nontunneling regime are analytically investigated. The optical paths of every constituent layer in a multilayer structure, as well as the parameters of every step of the stepwise potential barrier, are constrained by a generalized quarter-wave condition. No other restrictions on the structure geometry are imposed, i.e., the layers are arranged arbitrarily. We show that the density of states (DOS) spectra of the multilayer or barrier in question are subject to integral conservation rules similar to the Barnett-Loudon sum rule but occurring within a finite frequency or energy interval. In the optical case, these frequency intervals are regular. For the potential barriers, only nonperiodic energy intervals can be present in the spectrum of any given structure, and only if the parameters of constituent potential steps are properly chosen. The integral conservation relations derived analytically have also been verified numerically. The relations can be used in dispersion-engineered multilayer-based devices, e.g., ultrashort pulse compressors or ultracompact optical delay lines, as well as to design multiple-quantum-well electronic heterostructures with engineered DOS.

Propagation of classical waves in nonperiodic media: scaling properties of an optical Cantor filter.

Wave propagation through a subclass of deterministic nonperiodic media, namely, fractal Cantor multilayer structures are investigated theoretically as well as experimentally. Transmission spectra of Cantor structures are found to have two distinctive properties (scalability and sequential splitting) closely related to the geometrical peculiarities of the multilayers. A systematic correlation between structural self-similarity and spectral regularities of Cantor multilayers is established.