S. B. Brichkin

Hydrophilic semiconductor quantum dots

Comparative analysis of recent literature data on hydrophilization of semiconductor quantum dots, which are actively used at present in various fields, has been performed. The main methods of preparation of hydrophilic quantum dots are considered: synthesis of the particles in aqueous solutions; replacement of hydrophobic ligands with hydrophilic ligands in the shells stabilizing the particles; creation of a second, water-soluble shell around the hydrophobic particles; and various methods of post-preparative treatment to improve photoluminescent properties of quantum dots.

Supramolecular complexes based on cyclodextrins

A summary of the application of cyclodextrins (CDs) in the field of supramolecular chemistry has been given. Unique structural features of CDs, namely the separation of hydrophilic and hydrophobic groups, cause unusual physical and chemical properties of these molecules. The most important property of natural or chemically modified CDs is the ability to reversibly and selectively bind organic, inorganic, and biological molecules, forming inclusion complexes (ICs) of the “guest-host” type or nanostructured supramolecular assemblies. The most interesting examples of the application of ICs with CDs in pharmaceutical, food, and chemical industry, spectrometric analysis, separation technologies, of the use of CDs as models for molecular recognition in biology, as well as the cyclical component in the construction of supramolecular architectures (rotaxanes, pseudorotaxanes) are given in the review. The mechanism and methods of the formation of ICs, their properties and the methods of analysis have been described. Particular attention has been paid to molecular necklaces. One of the new promising directions of the application of CDs, namely, the preparation of nanosized materials, has been considered.

On the possibility of nonradiative energy transfer between hydrophobic quantum dots in solutions

The Förster resonance energy transfer between CdSe quantum dots with two different sizes has been studied in an organic solvent upon the formation of close-packed aggregates of quantum dots, with the aggregation being both spontaneous and induced by a precipitating solvent. The addition of a precipitant has been established to noticeably increase the efficiency of the energy transfer. It has been shown that the sizes and numbers of resulting aggregates may be controlled by varying the experimental conditions.

Colloidal quantum dots InP@ZnS: Inhomogeneous broadening and distribution of luminescence lifetimes

Indium phosphide colloidal quantum dots with a zinc sulfide shell, an average core diameter of 3 nm, a luminescence peak position of 600 nm, and a luminescence quantum yield up to 50% have been synthesized. By analyzing the stationary absorption and luminescence spectra in terms of the Kennard—Stepanov relationship, the values of homogeneous width and inhomogeneous broadening have been obtained, which determine the resulting width of the spectra: the corresponding full widths at half maximum (FWHM) were 31, 63, and 70 nm. From the value of inhomogeneous broadening and the sizing curve of indium phosphide, polydispersity of the synthesized particles has been estimated as 11%. Analysis of the luminescence decay kinetics has revealed three reproducible peaks with maxima near 4.35, 35 (main) and 200 ns in the lifetime distribution. It has been found that although repeated washing of the synthesized particles with methanol can decrease the quantum yield, the lifetime distribution observed remains constant, which in the context of the “blinking” effect indicates a very short luminescence decay time of the particles in the OFF-state.

Luminescent properties of CdSe quantum dots in dispersion media with different polarity

It has been found that the luminescence quantum yield of CdSe colloidal quantum dots (QD) synthesized in the presence of n-octadecylphosphonic acid and trioctylphosphine oxide significantly depends on the polarity of the medium in which they are dispersed and increases with decreasing the polarity of the medium. Different methods of increasing the quantum yield have been studied; the conditions have been found under which its value reaches 0.9, which is comparable to record values currently known for core@shell QD and is maximum for QD without an additional semiconductor shell. The effect of precipitating solvents on the luminescence efficiency of QD has been studied.

The solvent effect on luminescent properties of cadmium selenide quantum dots

It has been shown that the synthesis of CdSe quantum dots using a mixture of p-octadecylphosphonic acid (ODPA) and trioctylphosphine oxide (TOPO) as stabilizing ligands makes it possible to obtain nanoparticles with good luminescence characteristics without overcoating an additional semiconductor shell. It has been found that ODPA used as a stabilizing ligand in a mixture with TOPO in the synthesis of CdSe quantum dots can facilitate the preparation of particles with good spectral and luminescent properties. The luminescence intensity of these particles is increased by storage them in the dispersed state in an organic solvent. The luminescence quantum yield depends on the dielectric constant of the medium, the average size of the quantum dots, and the time of their holding in the solvent.

Synthesis and properties of colloidal indium phosphide quantum dots

Semiconductor colloidal quantum dots possessing unique spectral-luminescent characteristics are of great interest for the development of novel materials and devices, which are promising to be used in various fields. However, the contemporary high-quality quantum dots contain Cd, Pb, Hg, Se, and Te ions and are toxic, with this circumstance limiting their wide practical application. Therefore, the attention of researchers has recently been focused on AIIIBV semiconductor quantum dots—in particular, InP ones, which are markedly more environmentally safe. InP quantum dots have spectral characteristics similar to those of well-studied CdSe quantum dots and can, in principle, replace the latter in many cases, especially, taking into account their more pronounced size effect caused by the narrow energy gap and the large Bohr radius of the exciton. Moreover, the stronger InP covalent bond than the ionic one in AIIBVI semiconductors makes it possible to expect that they have a higher photostability and stability in active media. This work presents a review of the modern literature devoted to the synthesis and properties of colloidal indium phosphide quantum dots, which are very promising for use as substitutes of toxic cadmium-based quantum dots.

Hybrid system based on styrylquinoline ligand and CdS quantum dots

A new hybrid organo-inorganic system, QD-L, where QD is a nanoparticle (quantum dot) of CdS with a diameter of 2.65 nm and L is an organic photoactive ligand based on 2-(4-[9-mercaptononoxy]styryl)quinoline, is synthesized and characterized. The luminescence spectrum of QD-L is a superposition of the spectra of QD and ligand. The styrylquinoline ligand in the hybrid system retains the ability to trans-cis-photoisomerization; as a result it becomes possible to control the spectral-luminescent properties of the whole system under the action of light by transforming the ligand from one isomer state into another.

New hybrid photochromic materials with switchable fluorescence

A method for synthesizing a photochromic ligand and using it as a structural element in a new nanodimensional hybrid construction in which CdSe quantum dots are covalently bonded to a spiropyran molecule has been proposed. Such a hybrid construction makes it possible to reversibly control the system fluorescence using a change in spiropyran ligand structure induced by light with different wavelengths (a reversible conversion from a colorless closed form into a colored merocyanine form). The possibilities for using this type of hybrid material for photocontrollable devices in nanophotonics are discussed.

Phenidone Oxidation during Photoinitiated Chemical Reduction of AgBr Nanocrystals in Water Pools of Reverse Micelles

Photoinitiated chemical reduction of AgBr nanocrystals (synthesized in water pools of reverse micelles of Aerosol OT and sodium dodecyl sulfate) with phenidone was shown to yield 1-phenyl-3-hydroxypyrazole along with reduced silver. This becomes possible because of irreversible oxidation of phenidone (1-phenyl-3-pyrazolidone) used as a reducing agent, and the rate of 1-phenyl-3-hydroxypyrazole accumulation significantly increases in the presence of a silver halogenide. The formation of the dissociated form of 1-phenyl-3-hydroxypyrazole becomes more probable with decreasing diameter of the water pool of reverse micelles formed by both surfactants.