Multifunctional assistant acceptor modulated pyrenyl phenanthrimidazole derivatives for highly efficient blue and host-sensitized OLEDs

We have designed novel blue emitters namely, PPINCN, PPINCN-TPE and PPINCN-Cz with orthogonal D-A structure to harvest maximum exciton efficiency (EUE) through reverse intersystem crossing (RISC) with hot exciton mechanism....

Method of obtaining and studying the optical properties of carbon quantum dots.

The proposed method of synthesis of CQDs on the basis of nanoporous carbon obtained from plant raw materials. It is established that in the short-wave region a band is registered, which is due to the exciton mechanism of recombination, whereas in the long-wavelength region it is related to the state of defects. The kinetics of PL extinction is not strictly exponential, which most likely indicates the distributed nature of fading from individual emitters.

Резонансный безызлучательный перенос энергии в гибридных ассоциатах молекул тионина и коллоидных квантовых точек Ag-=SUB=-2-=/SUB=-S с различными механизмами люминесценции-=SUP=-*-=/SUP=-

We have considered the resonant nonradiative energy transfer in hybrid associates of thionine dye (TH^+) molecules and Ag_2S colloidal quantum dots (QDs) passivated with thioglycolic acid (Ag_2S/TGA) and Ag_2S QDs stabilized with gelatin (Ag_2S/Gel). Used samples of Ag_2S QDs possess luminescence, which arises by the exciton mechanism, as well as by the recombination mechanisms of holes with electrons localized at luminescence centers and of electrons with holes localized at the luminescence centers. The quenching of luminescence of Ag_2S/TGA QDs (1.8 nm) with a maximum at 630 nm and a decrease in the luminescence lifetime from 13.7 to 6.5 ns, which occurs upon association with TH^+ molecules, have been established. On the contrary, for associates of Ag_2S/TGA QDs (5.5 nm) with TH^+ molecules, we have observed the quenching of luminescence of the dye and a decrease in the lifetime of this luminescence from 0.43 to 0.3 ns, as well as an enhancement of luminescence of QDs. In the case of hybrid association with TH^+ molecules, the luminescence enhancement of Ag_2S/Gel QDs (1.6 nm) has been established, which results from the recombination of free holes with electrons localized at luminescence centers. Based on our analysis of the luminescence kinetics of the dye, we have inferred the occurrence of resonant nonradiative energy transfer from TH^+ molecules to centers of recombination luminescence in Ag_2S/TGA (5.5 nm) and in Ag_2S/Gel (1.6 nm) QDs with its maxima at 950 and 1205 nm, respectively. For Ag_2S/TGA QDs (2.2 nm), which luminesce with a maximum at 620 nm by the exciton mechanism, we have observed a significant overlap both between the luminescence spectra of QDs and TH^+ and between their absorption spectra. Close parameters of the luminescence kinetics for both the initial components and their associates indicate the energy transfer, which is realized in opposite directions.

LASER INDUCED METAL INSULATOR TRANSITION THROUGH EXCITON MECHANISM IN QUANTUM WELL SYSTEMS

Within the effective mass approximation, the binding energies of a Wannier exciton in a GaAs-Ga 1-x Al x As quantum well in an electric field are investigated using a variational method. The binding energiesare obtained upon illlumination by laser radiation. The binding energy decreases as the well size increases when the size of the well is beyond 50 Å. The above behavior is for a quantum well of finite confinement. We have investigated the metal-insulator transition in such a system and report the values of critical concentrations of excitons at which metal-insulator transition occurs for different well dimensions. The calculated diamagnetic susceptibility shows the catastrophic behavior at the critical concentration.

DOPING DEPENDENT ELECTRONIC STRUCTURE OF CUPRATES AND THE EFFECTIVE LOW ENERGY HAMILTONIAN FOR THE MAGNETIC PAIRING

The properties of the normal and superconducting phases of p- and n-type cuprates are investigated in the appropriate low-energy models in the approximation beyond Hubbard I considering spin fluctuations. Calculated chemical potential dependence on doping, Fermi surface and Tc(x) phase diagram for n-type cuprates are in remarkably good agreement with the experimental ones. Comparison of the singlet-triplet t-J model with simple t-J model shows that the spin-exciton mechanism originated from singlet-triplet hybridization leads to small contribution to the Tc(x) - optimal doping value becomes slightly lower and the maximum value of Tc become slightly higher.