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.
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.
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.
In this study, we analyzed the effect of the composition and thickness of shell material on morphology, structure and optical properties of ultrathin CdSe/CdS, CdSe/CdS/ZnS and CdSe/ZnS core-shell ...nanoplatelets. It is shown that the growth of CdS and ZnS shells on ultrathin CdSe nanoplatelets with excitonic absorption at 463 nm leads to the formation of flat CdSe/CdS and CdSe/CdS/ZnS and folded CdSe/ZnS core-shell heterostructures, respectively. The tuning of the first excitonic transition in a range of 510–635 nm is shown by changing the composition and thickness of the shell material. Despite large lateral sizes, the CdSe/CdS and CdSe/CdS/ZnS core-shell nanoplatelets showed narrow emission bands with about 18–21 nm width. Emission width of the CdSe/ZnS heterostructures is shown to be thickness dependent and broader than that of CdSe/CdS and CdSe/CdS/ZnS heterostructures. Such control of the electronic structure of 2D core-shell nanoparticles, simply by changing the thickness and composition of the shell material may be attractive for the light-emitting device technology and lasers.
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•The PL of CdSe/CdS and CdSe/ZnS NPLs can be changed by composition and thickness of the shell in a range of 530-635 nm.•The morphology of ultrathin CdSe/CdS and CdSe/ZnS NPLs can be changed from flat-sheets to folded-sheets.•The broadening of the absorption and emission bands of ultrathin CdSe/CdS and CdSe/CdS/ZnS NPLs is homogenous.
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.
Nonlinear absorption of colloidal solution of core/shell CdSe/CdS nanoplatelets (NPLs) in the case of resonant and nonresonant stationary excitation of the electron/light-hole and electron/heavy-hole ...exciton transitions was investigated. We have revealed the induced bleaching simultaneously of both exciton transitions. The peculiarities of the nonlinear change in absorption were associated with saturation of exciton transitions absorption due to phase space filling, energy up- and down-conversion mechanisms.
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.
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