Search

Four novel 1,3-diketonate Eu 3 + complexes bearing pyrazole moieties as main ligands and a 4,7-Diphenyl-1,10-phenanthroline (bathophenanthroline) ancillary ligand were synthesized. The number of fluorine atoms in the main ligand was varied from 3 to 13. From spectroscopic studies of the synthesized complexes we conclude that increasing the degree of fluorination results in a significant rise in the quantum yield and sensitization efficiency. With further extension of the fluorinated chain length, saturation of these characteristics was observed. The maximum obtained values of the quantum yield and sensitization efficiency were 56% and 99%, respectively. In order to reveal the potential of the complexes for OLED applications, electroluminescent devices based on these compounds were fabricated and their performance was studied. It was found that the quantum efficiencies of the OLEDs and the sensitization efficiencies exhibit similar behaviour depending on the degree of fluorination of the ligands in the complexes.

We studied luminescent properties of two Nd 3 + complexes with two different ligands. The first one was 1,3-diketone bearing a pyrazole fragment and the second ligand was either 1,10-phenanthroline or EtOH. For the ligand environment composed of 1,3-diketone and 1,10-phenanthroline the position of the hybrid triplet level was as low as 18200 cm − 1 . The spectral features specific to Nd 3 + emission observed in the photoluminescence spectra of the complexes under optical excitation provided the evidence for ion-centered luminescence. Radiative transitions were identified using the obtained spectroscopic data. Corresponding diagram of the energy levels of the complex with 1,10-phenanthroline ligand was developed. Possible energy transfer pathways were discussed.

We performed spectroscopic investigations of four novel Sc(III) metal-organic complexes with β -diketonate ligands. It was demonstrated that bonding the ligands with an optically passive Sc(III) ion leads to sensitization of the luminescence of the complexes and affects their optical absorption spectra. Luminescence decays of the complexes exhibit non-exponential behaviour. From spatially-resolved decay measurements we evaluated the number of different sites responsible for the luminescence in the investigated complexes. Small variations of the ligand structure significantly affects the wavelength of emission maximum. This phenomenon may occur due to the difference in crystal packing of the complexes or formation of charge-transfer states.

The luminescent properties of hybrid nanostructures constructed from colloidal quantum dots (QDs) of CdS passivated with thioglycolic acid, europium(III) tris(tenoyltrifluoroacetonate), and methylene blue dye molecules are studied. Spectral features typical for the formation of core/shell QDs of the CdS/CdS:Eu3+ type are found. It is noted that the adsorption of the europium complex at the QD interfaces and the formation of QDs of the CdS/TGA/Eu3+ are probable. Spectral patterns that reveal nonradiative energy transfer from the recombination luminescence centers of CdS QDs to the Eu3+ ions in the CdS/CdS:Eu3+ and CdS/TGA/Eu3+ structures are obtained. This is manifested in quenching the recombination luminescence of QDs and in the ignition of the intracentric luminescence of Eu3+, which enhance with an increase in the concentration of the europium complex. When such structures are combined with methylene blue molecules, the half-width of the absorption spectra is found to increase by 10–15% with an unchanged position of the absorption band maximum. With an increase in the concentration of methylene blue molecules, decreases in the intensity of the recombination luminescence band of CdS QDs at a wavelength of 530 nm and in the luminescence intensity of Eu3+ ions and simultaneously the rise up of the fluorescence of methylene blue at a wavelength of about 675 nm are observed. At the same time, a decrease in the luminescence lifetime of the bands of QDs and europium ions are observed. It is concluded that the nonradiative excitation energy transfer from both the recombination luminescence centers and Eu3+ ions to methylene blue molecules takes place.

In this study, two novel Pr 3 + complexes with different 1,3-diketonate ligands were synthesized and investigated. To study the effect of the ancillary ligand on the energy transfer mechanisms in the complexes, a phenanthroline ligand was introduced. To take into account the influence of the ligand environment composed of different ligands on the energy transfer and relaxation processes, we compared the synthesized compounds with a similar complex containing the phenanthroline ligand. The spectroscopic studies in the visible and near-infrared spectral regions were supplemented with DFT and TD-DFT calculations. We found two ligand-to-ligand charge transfer (LLCT) states, with one state corresponding to energy transfer between 1,3-diketones and the other – to energy transfer from the 1,3-diketone to the phenanthroline motif. It was demonstrated that optical excitation via the latter channel leads to a fourfold increase in the luminescence quantum yield as compared with excitation via the π - π ∗ transitions in 1,3-diketones. Moreover, both LLCT states provide sensitization of the Pr 3 + luminescence involving the 3 P 0 and 3 P 1 levels.

We studied luminescent properties of Pr 3 + complex with pyrazole and 1, 10-phenanthroline ligand environment. It was demonstrated that the complex exhibits so-called “antenna” effect which involves the electronic excitation transfer from the ligands to the rare-earth ion. The observed complex structure of the luminescence spectrum specific to Pr 3 + indicates that in the investigated compounds the luminescence originates from the rare-earth ion exclusively. The obtained data provided a means to identify the electronic transitions in the ion and to develop the corresponding energy diagram. Fluorescence lifetime imaging revealed uniform distribution of luminescence decay times for the Pr 3 + complex crystalline phase. Consequently, the Pr 3 + complex under study has one type of emission sites.

The efficiency of electronic-excitation energy transfer from organic semiconductor TPD to CdSe/CdS/ZnS nanocrystals passivated with different organic ligands is investigated. It is shown that the rate of energy transfer from TPD to nanocrystals decreases with increasing thickness of the passivation coating. It is suggested that the Forster mechanism is responsible for the excitation transfer.

We present a composite material based on polymer matrices doped with a new europium(III) complex exhibiting high quantum yield. The Eu(III) complex was introduced into two types of polymer matrices. We investigate the concentration influence of the complex embedded into polymers on luminescent properties of the composite material. This Eu(III) complex proved to be highly dispersible in polymers and compatible with ink-jet technology.

We report on the results of analysis of the kinetics of charge–discharge current of Panasonic supercapacitors in a wide range of time from 10–1 to 104 s. The non-Debye behavior of relaxation observed earlier by us and other authors is confirmed experimentally, and the influence of the supercapacitor charging regime on this process for various previous histories (values of applied voltage, charging time, and load resistance) is analyzed. The results are compared with available experimental data for paper–oil and electrolytic capacitors and with the results of calculations in the linear response model. It is found that in contrast to conventional capacitors, the response of the supercapacitor under investigation to variations of the charging regime does not match the linear response model. The relation of this nonlinearity to processes in the double electric layer, the morphology of the porous electrode, and the effect of charge reversal in pores is considered.

A series of novel highly NIR-emitting Nd 3 + complexes with specially designed 1,3-diketones bearing a pyrazole moiety and a linear C x F 2 x + 1 group ( x = 1 , 3 , 6 ) was obtained and exhaustively investigated. It was demonstrated that for the complexes with an increased number of fluorine atoms, the triplet level energy of the ligands is decreased and phonon relaxation processes are suppressed. This provides a remarkable increase in the photoluminescence quantum yield up to 1.1%, which is close to the highest values reported for Nd 3 + complexes with 1,3-diketones. The photoluminescence spectra of the complexes exhibited the Stark splitting indicative of non-cubic symmetry. Low symmetry of coordination environment was confirmed by the X-ray structural data and analysis of calculated Judd–Ofelt intensity parameters. Besides, it was revealed that the most intense band in the PL spectrum is attributed to the 4 F 3 ∕ 2 → 4 I 9 ∕ 2 transition (at 880 nm) which is commonly rather weak for simple diketonate complexes. The calculations showed that the unexpectedly high branching ratio of the 4 F 3 ∕ 2 → 4 I 9 ∕ 2 transition raises with elongation of the fluorinated chain and reaches 59% for the complex with x = 6 . The studies were conducted for solutions of the complexes as well as for solid samples, and the corresponding changes in their optical behavior were discussed. Uncommon properties of the synthesized Nd 3 + complexes make them promising materials for various state-of-the-art luminescent applications, e.g., luminescent markers with an unusual spectral intensity distribution. Based on the electroluminescence studies, we also estimated the potential of the complexes for purely NIR-emitting OLEDs fabrication.

A novel, to the best of our knowledge, approach to the design of the single-photon sources emitting in the spectral regions of 1060 and 1337 nm was developed. A unique hybrid structure based on colloidal CdSe/CdS/ZnS nanocrystals and neodymium(III) 1,3-diketonate was created. Direct energy transfer from the CdSe/CdS/ZnS single nanocrystal to the near-infrared (NIR) luminescent Nd(III) complex was observed and investigated by spectroscopic methods. The single-photon emission mode was confirmed for the novel hybrid source by Hanbury Brown and Twiss experiments.

Two new Sm3+ complexes with pyrazolic β-diketones bearing a CF3 group acting as main ligands and with 2,2’-bipyridine or 1,10-phenanthroline being the ancillary ligand were studied, and their energy level structure was established. Stark splitting observed in the photoluminescence spectra of the complexes points to their non-cubic symmetry, confirmed by the calculated Judd-Ofelt intensity parameters. Internal quantum yields obtained for the compounds by the Judd-Ofelt calculations were of the order of 5.5%, whereas the measured external quantum yields were 0.75% and 1.5% for Sm3+ complexes involving 2,2’-bipyridine and 1,10-phenanthroline ancillary ligands, respectively, with the corresponding sensitization efficiencies calculated as 0.16 and 0.26. It was demonstrated that replacing the 1,10-phenanthroline ancillary ligand with 2,2’-bipyridine provides an increase in the intensity of 650 nm emission of the Sm3+ complexes, with the branching ratio reaching 55%. Intensive emission of the studied complexes at 650 nm offers hope for their use as spectrally pure red emitters.

The temperature dependence of the photoluminescence intensity of colloidal CdSe nanocrystals having 5 nm in diameter was studied. It was demonstrated that the photoluminescence intensity exhibits a hysteresis at temperatures below 220 K. This effect was explained by a model taking into account formation of an additional nonradiative relaxation channel associated with Auger recombination promoted by hole trapping on the surface of the nanocrystals. The activation energy of the hole release process obtained in the framework of the model was 0.7 eV.

It is shown that the finite-term representation of current relaxation in supercapacitors with a set of exponential functions fails to approximate it at long time, meanwhile the one-term approximation with the stretched fractional exponent gives a good agreement with experimental data both at short- and long-time asymptotics.