The nonlinear absorption and photoluminescence of CdTe/CdSe nanotetrapod colloids have been studied by the pump–probe method for the case of single-photon nonresonance excitation of excitons. ...A competition between the short-wave and long-wave shifts of the peak of photoluminescence associated with an indirect electron–hole transition, which is observed with increasing excitation radiation intensity, has been found and explained. The former shift is associated with an increase in the one-dimensional exciton radius after the exciton state occupation, and the latter shift may be attributed to the charge-induced Stark effect and local heating of nanotetrapods as a result of electron–phonon interaction at nonresonance excitation of the system.
In experiments on mice the study of the radioprotective and radiotherapeutic efficacy of the combined use of the selenium-containing feed additive DAFS-25k and the iodine-containing preparation ...Monclavit-1 was carried out. It has been shown that intragastric administration of DAFS-25k oil solution 3 hours before the total, external, single exposure to γ-radiation, and the subsequent (in 12 hours) intragastric administration of an aqueous solution of Monclavit-1, increases the survival rate of irradiated animals to 67% versus 17% in the control animals. The mechanisms of radioprotective efficacy are assumed to be the antioxidant activity of selenium compounds in DAFS-25k, normalization of thyroid function and relief of gastrointestinal syndrome due to the pronounced antimicrobial activity of Monclavit-1.
This work devotes to investigation of two-photon absorption in a colloidal solution of nanoplatelets CdSe/CdS (3.5 and 2 monolayers of CdSe core and CdS shell respectively) in the case of light- and ...heavy-hole exciton excitation (1lh-1e, 536 nm) and (1hh-1e, 578 nm) by femtosecond laser radiation (1064 nm, 100 kHz). An open-aperture z-scan technique was utilized to measure nonlinear two-photon absorption coefficient which was found as β = 0.08 ± 0.01 cm/GW, two-photon absorption cross sections σ
(2)
≈ 1.5 × 10
6
GM and nonlinear refraction index γ ≈ –5 × 10
–16
cm
2
/W. The revealed features of the measured
z
-scan dependencies can be the evidence of amplified spontaneous emission in the colloidal solution of CdSe/CdS nanoplatelets at high intensity of two-photon excitation.
Nonlinear change in transmission and photoluminescence of the colloidal CdSe nanoplatelets in the case of stationary exciton excitation by the third harmonic of mode-locked Nd
3+
:YAP laser pulses ...allowed to identify peculiarities of the exciton dynamics. The values of saturation intensity were determined from the measured differential transmission spectra. The revealed broadening and red shift of the photoluminescence spectra can be the evidence of the formation of trions and their radiative recombination at room temperature.
It is shown that the impedance spectroscopy allows identification of the resistive switching mechanisms in complex composite structures. This statement was demonstrated on an example of organic based ...sandwich structures with a modified polymer matrix as an active element. The impedance spectroscopy scanning was performed for a series of intermediate states formed within the switching process. Analysis of the experimentally obtained impedance spectra shows that the electron transport is provided by delocalized charge carriers and proceeds via conducting filaments formed in a highly resistive matrix. The filament configuration changes during the switching. With the shift from isolating to conducting states, single isolated filaments are reorganized into a branched network.
The results of study of primary melt inclusions in accessory Cr–spinelides from dunite have revealed features of the chemical compositions of high-magnesium picrite–basalt melts that formed ...ultramafic massifs of the Siberian Platform. Computational modeling (with the PETROLOG and PLUTON software) using the inclusion compositions allowed determination of the crystallization temperatures of olivines from dunites of the Guli (1520–1420°С), Konder (1545–1430°С), Inagli (1530–1430°С), and Chad (1460–1420°C) massifs. The Cr–spinellids from the same complexes crystallized at Guli (1410–1370°С), Konder (1420–1380°С), Inagli (up to 1430°С), and Chad (1430–1330°С). Overall, computational modeling has revealed two types of trends of high-Mg melt evolution on the Siberian Platform. The first type is characteristic of the Guli Pluton, with the following rock sequence: dunite–pyroxenite–alkalic rocks. The second type occurs in the Konder massif, with a different sequence: dunite–kosvite–pyroxenite and olivine–diopside rocks.
Comparative analysis of the composition and formation conditions of the dunite–pyroxenite association of the Guli Pluton and ultramafic vulcanite (meimechite) showed the similarity of their initial ...melts and the same type of crystallization, demonstrating the cumulative origin of dunite.
Tip-enhanced Raman scattering (TERS) has recently emerged as a powerful technique for studying the local properties of low dimensional materials. Being a plasmon driven system, a dramatic enhancement ...of the TERS sensitivity can be achieved by an appropriate choice of the plasmonic substrate in the so-called gap-mode configuration. Here, we investigate the phonon properties of CdSe nanocrystals (NCs) utilizing gap-mode TERS. Using the Langmuir-Blodgett technique, we homogeneously deposited submonolayers of colloidal CdSe NCs on two different nanostructured plasmonic substrates. Amplified by resonant gap-mode TERS, the scattering by the optical phonon modes of CdSe NCs is markedly enhanced making it possible to observe up to the third overtone of the LO mode reliably. The home-made plasmonic substrates and TERS tips allow the analysis of the TERS images of CdSe phonon modes with nanometer spatial resolution. The CdSe phonon scattering intensity is strongly correlated with the local electromagnetic field distribution across the plasmonic substrates.
We demonstrated resonant/non-resonant gap-mode TERS on CdSe nanocrystals analyzing of LO (up to 3rd order), SO/TO phonons, as well as Se vibrational modes.
Abstract
Two-photon processes in CdSe/CdS nanoplatelets were investigated under high intensity excitation by femtosecond laser radiation (1064 nm, 100kHz). The open-aperture z-scan technique and the ...measurement of photoluminescence spectra were utilized for studying their nonlinear optical properties. As a result, two-photon absorption and amplified spontaneous emission at high intensity were found in these nanoplatelets.
The features of the nonresonant absorption of CdSe nanoplatelets with a CdS shell are studied in the case of excitation to the exciton absorption edge by high-power nanosecond laser pulses. It is ...shown that the exciton–phonon interaction plays a key role in the processes of nonresonant absorption of photons in colloidal nanoplatelets. The observed features of the nonlinear change in absorption are explained by the effect of the partial filling of the exciton phase space owing to the interaction with longitudinal optical phonons.