The results of molecular dynamics simulation of the crystal structure of the currently most studied CQDs, based on cadmium selenide nanoparticles, are presented, and issues concerning the structure of the ligand shell of these nanoparticles, primarily made of trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO) molecules, which act as a medium and as precursors in the chemical reaction that results in the formation of CQDs, are discussed in detail.
Mechanisms of homogeneous and inhomogeneous broadening of absorption and photoluminescence spectra of CQDs are discussed. The influence of the nature of solvents, their dielectric characteristics, and the type of stabilizing ligands on the luminescent properties of CQDs, including the luminescence blinking effect, is considered.
Various currently known methods for producing quantum dots are described in detail, including the most promising method of high-temperature colloidal synthesis (HTCS). Using the HTCS technique, it is possible to cope quite well with the task of obtaining a relatively perfect structure of colloidal quantum dots (CQDs) and achieve record-breaking narrow size distributions of CQDs. During the synthesis of nanoparticles, high-temperature annealing of their structure occurs. That is why this method has become so widespread and caused such a rapid increase in publication activity.
Nanoclusters of colloidal quantum dots (CQDs) are considered, the luminescent properties of which largely determine the electronic-excitation transport processes described by the Förster mechanism of inductive resonance interaction of CQDs. A simple theoretical model is proposed taking into account the Kennard–Stepanov relation, with the help of which numerous experimental results are analyzed.
The physical mechanism of the quantum size effect, which determines the main feature of the size dependence of absorption and photoluminescence spectra of nanoparticles of semiconductor materials, is outlined, and the effects of multiexciton generation and luminescence blinking of colloidal quantum dots are discussed.
A brief review of the well-known laws and rules of photoluminescence is given, and it is shown that these laws usually do not hold for CQD solutions. It has been shown that this is due to a special mechanism for the formation of the luminescent properties of CQDs. The derivation of a new universal law of photoluminescence, applicable to any type of luminophores, which has recently been substantiated theoretically and verified experimentally using the example of CQDs, is presented.
The laser material Y3Al5O12 (YAG), originally known in the form of a single crystal, has become widespread and widely commercialized in the form of optical ceramics. The desire to expand by the size effect the functionality of materials made from nanocrystals actualizes studying the influence of their structure on the optical (vibrational and electronic) and other properties of new promising materials with the YAG base, including glass ceramics. In this work, models of crystalline yttrium aluminum garnet fragments have been calculated using the DFT/uPBEPBE/SDD, DFT/uPBEPBE/lanl2DZ, and DFT/uB3PW91/SDD methods. Infrared spectra have been calculated using the DFT/uPBEPBE/lanl2DZ method, and absorption bands at calculated wave numbers have been correlated with the measured ones. The electronic absorption spectrum and level energies have been calculated using the DFT/RB3PW91/SDD method.
The stress–strain diagram of a polymer composite material based on rubber PDI-3A filled with thermally expanded graphite or potassium chloride has been studied before and after microwave treatment for 300, 600, 900, and 1200 s. It has been found that the ultimate tensile strength and strain increase twofold after a 300-s microwave treatment and testing at 223 K. A significant decrease in the stress–strain properties of the synthesized composites with an increase in the test temperature or microwave treatment time is observed.
The radiolysis of liquid and boiling hexafluoroacetylacetone has been studied. The structure of the main radiolysis products indicates the predominance of C–CF3 and C–F bond cleavages. Ten compounds including monoketones, trifluoroacetic acid, keto alcohols, and tautomeric tetraketones were formed. Carbon monoxide was the main gaseous product, and its yield increased under boiling conditions. The initial yields of hexafluoroacetylacetone degradation were 0.29 ± 0.2 and 0.32 ± 0.2 µmol/J at 293 and 343 K, respectively. No accumulation of free HF was observed at low doses. The products of radiolysis are less diverse than those in acetylacetone; this is due to enhancement of the cage effect and to an increase the Onsager radius and the ability of trifluoromethyl groups to dissipate excitation energy.
An analysis of the luminescence spectra of plasma formed during laser ablation of a gold target immersed in superfluid helium at a laser radiation power density below the breakdown threshold of liquid helium showed that the ionization energy of the Au2+ ion should be no lower than 34 eV.
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