A. V. Prudnikau

Formation of structures based on semiconductor quantum dots and organic molecules in track pore membranes

We prepared hybrid structures based on CdSe/ZnS quantum dots and organic azo-dyes and porphyrin molecules embedded into polymer track pore membranes. The quenching of the quantum dots photoluminescence and the shortening of its decay time, accompanied in the latter case by a porphyrin sensitized photoluminescence, present a clear evidence of the efficient energy transfer in these structures. The proposed quantum-dot/azo-dyes and quantum-dot/porphyrin structures can be used in different microfluidic systems for, e.g., sensing of metal ions or efficient singlet oxygen generation.

Reversible photoluminescence quenching of CdSe/ZnS quantum dots embedded in porous glass by ammonia vapor.

The photoluminescence response of semiconductor CdSe/ZnS quantum dots embedded in a borosilicate porous glass matrix to exposure to ammonia vapor is investigated. The formation of surface complexes on the quantum dots results in quenching of the photoluminescence and a shortening of the luminescence decay time. The process is reversible, desorption of ammonia molecules from the quantum dot surface causes the photoluminescence to recover. The sensitivity of the quantum dot luminescence intensity and decay time to the interaction time and the reversibility of the photoluminescence changes make the CdSe/ZnS quantum dots in porous glass system a candidate for use as an optical sensor of ammonia.

Size-dependent room-temperature luminescence decay from PbS quantum dots

We study size dependence of kinetic and spectral properties of near-infrared luminescence from PbS quantum dots in colloidal solution. Luminescence lifetimes are found to lie between 250 ns for the largest quantum dots and 2:5 μs for the smallest ones, while the Stokes shift is found to increase from 4-5 to 300 meV. These results are explained by the presence of the long-living in-gap state, with the size-dependent energy. Analytical modeling shows that the relaxation from this state is dominant in small quantum dots and negligible in large ones. Biexponential luminescence decay with the size-dependent recombination rates is predicted for quantum dots of all sizes.

The effect of an external electric field on photoluminescence of CdSe colloidal nanoparticles of different topologies

Photoluminescence of CdSe colloidal nanocrystals of different topologies in an external electric field has been studied. It has been found that quenching of photoluminescence, which takes place in quantum dots, is proportional to the square of the field, and in elongated nanocrystals quenching of photoluminescence is proportional to the square root. A physical model of the mechanism of quenching based on tunneling of free charges through potential barrier nanocrystal/matrix has been proposed.

Analysis of structural and chemical features of CdHgSe nanocrystals via resonance Raman spectroscopy

We investigate quantum dots (QDs) of ternary compounds CdXHg1-XSe with 0<X<1 using a Raman scattering technique at room temperature. We obtained the correlation between QDs chemical composition and the frequencies of CdSe-like LO and the HgSe-like TO and LO modes. It is shown that the crystalline structure of original CdSe QDs used for Cd/Hg substitution, either zinc blende or wurtzite affects strongly on structural properties of resultant CdXHg1-XSequantum dots.

Optical properties and aging of PbS quantum dots embedded in a porous matrix

PbS quantum dots (QDs) with diameter of 2.9-7.4 nm were embedded into a porous matrix. The samples prepared by developed low-cost effortless method demonstrate linear dependencies of optical density and luminescence intensity on the QDs concentration and perfect homogeneity. Optical properties of quantum dots in the matrix were studied using absorption and steady-state and time-resolved photoluminescence spectroscopy. Luminescence lifetimes were found to be size-dependent and increase with decreasing of QDs size. The aging behavior of PbS QDs in a porous matrix was explored for a variety of QDs sizes. The energy transfer process in quasi-monodispersed PbS QDs ensemble was discovered.

Raman analysis of chemical substitution of Cd atoms by Hg in CdSe quantum dots and rods

Abstract. We investigate nanocrystals of ternary compounds CdXHg1−XSe with 0<X<1 using a Raman scattering technique at room temperature. We obtained the correlation between nanocrystal (NC) chemical composition and the frequencies of CdSe-like LO and the HgSe-like TO and LO-modes. It is shown that the crystalline structure of the original CdSe NCs used for Cd/Hg substitution, either zinc blende or wurtzite, strongly affects the structural properties of the resultant CdXHg1−XSe quantum dots and rods.

Optical properties of two-dimensional (2D) CdSe nanostructures

The resonant and off-resonant Raman spectra of optical phonons in two-dimensional CdSe nanocrystals of 5, 6, and 7 monolayers are analysed. The spectra are dominated by SO and LO phonon bands of CdSe, whose frequencies are thickness-independent in the off-resonant Raman scattering but demonstrate an evident thickness dependence in the case of the resonant Raman scattering.