The Peculiarities of Singlet Electronic Excitation Energy Transfer Processes in Alq3 Films

The absorption and luminescence of new boron-containing dyes in two-component films of Alq3 (matrix)-dye(impurity) (obtained by the method of thermal vacuum deposition) are studied. The comparison of the spectra of absorption, fluorescence, and fluorescence excitation of a dyes in one-component solutions and double-component films shows the existence of the effective electronic excitation energy transfer (EEET) from the matrix to dye molecules. Time-resolved spectra of two-component films also manifest strong EEET in these systems. For the estimation of the average exciton spreading length in Alq3 films, the diffusion model of the motion of singlet excitons is used. The diffusion coefficient is evaluated using time-resolved spectroscopy. The optimum concentrations of dyes in a light-emitting layer of OLED are evaluated based on experimental data and the used model of EEET.

Люминесцентные свойства соединений европия(III) с хинолиновой кислотой и фосфорсодержащими нейтральными лигандами

Luminescent mixed-ligand europium(III) complexes with quinolinic acid and phosphorus-containing neutral ligands with a dimeric structure of the composition Eu_2(QA)_3 · 3Н_2О, Eu_2(QA)_3 · D · 2Н_2О, where QA is quinolinic acid and D is hmpa (hexamethylphosphortriamide), tppo (triphenylphosphinoxide), (hmpa), or Et_6pa (hexaethylphosphortriamide), are synthesized. The thermal and spectral-luminescent properties of the synthesized complex mixed-ligand europium(III) compounds are studied. It is shown that the detachment of water and neutral ligand molecules during thermolysis occurs in two stages with endothermic effects and that the complex compounds are stable at temperatures up to 320°С. It is found by IR spectroscopy that quinolinic acid coordinates to the europium(III) ion by two carboxylate ions. The low luminescence intensity of mixed-ligand europium(III) quinolinates is explained by inefficient electronic excitation energy transfer from quinolinic acid and phosphorus-containing neutral ligands to europium ions.

Передача энергии электронного возбуждения в масcиве квантовых точек CdS на квазидвумерной поверхности

The optical spectra of films composed of spherical silicon-dioxide particles coated with small-radius CdS quantum dots are recorded and analyzed. Large shifts of the absorption and photoluminescence bands are detected and studied in relation to the concentration of quantum dots and to the pumping density and wavelength. Analysis of the experimental data shows that the effects are due to electronic excitation energy transfer by particles through the mechanism of tunneling induced by a strong interaction between quantum dots. The results obtained at low pumping densities and different excitation wavelengths make it possible to describe the size distribution of CdS quantum dots. This distribution can be adequately approximated with a Gaussian function.

Energy transfer in liquid and solid nanoobjects: application in luminescent analysis

Radiationless resonance electronic excitation energy transfer (ET) is a fundamental physical phenomenon in luminescence spectroscopy playing an important role in natural processes, especially in photosynthesis and biochemistry. Besides, it is widely used in photooptics, optoelectronics, and protein chemistry, coordination chemistry of transition metals and lanthanides as well as in luminescent analysis. ET involves the transfer of electronic energy from a donor (D) (molecules or particles) which is initially excited, to an acceptor (A) at the ground state to emit it later. Fluorescence or phosphorescence of the acceptor that occurs during ET is known as sensitized. There do many kinds of ET exist but in all cases along with other factors the rate and efficiency of ET in common solvents depends to a large extent on the distance between the donor and the acceptor. This dependency greatly limits the efficiency of ET and, correspondingly, does not allow the determination of analytes in highly diluted (10–9–10–15 M) solutions. To solve the problem of distance-effect, the effects of concentrating and bring close together the donor and acceptor in surfactant micelles (liquid nanosystems) or sorption on solid nanoparticles are used. Various approaches to promote the efficiency of ET for improvement determination selectivity and sensitivity using liquid and solid nanoobjects is reviewed and analyzed.