Unsymmetrical 4,4 '-biphenyl derivative with tris(trifluoromethyl)germylethynyl -C =C-Ge(CF3)3 and ferrocenylethynyl Fc-C =C- substitutes have been prepared ( 21 ), its properties have been studied and compared with those full non-fluorinated analogue of trimethylgermylethynyl -C =C-Ge(CH3)3 compound ( 20 ). UV-visible, absorption, steady state, and time-resolved fluorescence spectra in solution for these germanium and a number of similar compounds ( 15 -17, 22 ) have been investigated. The process of photoinduced electron transfer from the n-conjugated system to the germanium center is confirmed for 21 , as well as for the first time discovered earlier [19] in the 4-biphenyl -C =C-Ge(CF3)3 molecule ( 9 ). It was found that the lifetime of the radical-ion pair 21 in the excited state (kCR2 = 1.2 x 10 5 s-1 ) is approximately an order of magnitude longer than for 9 , which can be explained by the stabilizing effect of the electron donor Fc-C =C- group. Density-functional theory (DFT) computations was used to calculate the optimized geometry of 21 in excited state, and two main bands in the emission spectrum at laser excitation (340 and 386 nm) an excellent fit to the experimental data. An additional data on the nature of the (CF3)3Ge group, including geometry, electronegativity, and contributions 4d AOs of germanium into lowest unoccupied molecular orbital (LUMO) in a wide range of fluorinated and non -fluorinated compounds were also calculated. The molecular structure of compound 21 was determined by X-ray structural analysis. In the crystal lattice of 21 , numerous intermolecular F middotmiddotmiddotF interactions shortened in comparison with the van der Waals radii were detected, which leads to the formation of quasi-two-dimensional fluorinated layers in crystals.(c) 2022 Elsevier B.V. All rights reserved.

The results of the investigations of photoluminescence and photoluminescence excitation spectra together with the transmission electron microscopy structural analysis of AlxGa1-xAs nanowires grown by molecular beam epitaxy with nominal aluminum content of 0.2 - 0.7 are presented. It is shown that the investigated nanowire possess wurtzite phase and the spectral positions of their luminescence band differ significantly from the bulk sphalerite type alloys of similar content.

Herein, complexes [ZnL]2 (1), {(H2O)Zn(μ-L)Yb[OCH(CF3)2]3} (2), {[(CF3)2HCO]Zn(μ-L)Yb[OCH(CF3)2](μ-OH)}2 (3), and [(H2O)Ln2(L)3] (Ln = Yb (4) and Gd (5)) containing a bridging Schiff-base ligand (H2L = N,N'-bis(3-methoxy salicylidene)phenylene-1,2-diamine) were synthesized. The compounds 1-4 were structurally characterized. The ytterbium derivatives 2-4 exhibited bright NIR metal-centred photoluminescence (PL) of Yb3+ ion under one- (λex = 380 nm) and two-photon (λex = 750 nm) excitation. The superior luminescence properties of complex 2, which was suggested as a marker for NIR bioimaging, were explained via the strong absorption of the 375 nm LMCT state of the ZnL chromophore, efficient energy transfer from ZnL towards Yb3+ through a reversible ligand-to-lanthanide electron transfer process, and absence of luminescence quenchers (C-H and O-H groups) in the first coordination sphere of the rare-earth atom.

The processes associated with the transfer of excitonic excitations between tunnel-uncoupled quantum wells (QW) and the influence of the local electric field were investigated in AlGaAs/GaAs heterostructures by the method of photoluminescence excitation (PLE) spectroscopy at low (4.2 K) temperature. The variation in the intensity of photoluminescence (PL) from the wider QW under resonant excitation of excitonic transition in the adjacent narrow QW has been observed. The difference in the PL maximum position and intensity of the wider QW under resonance excitation of the narrow one is explained by the influence of quantum-confined Stark effect on the process of exciton recombination.

В гетероструктурах AlGaAs/GaAs методом спектроскопии возбуждения фотолюминесценции исследовались процессы, связанные с переносом экситонных возбуждений между туннельно-несвязанными квантовыми ямами и изменением встроенного электрического поля. Наблюдалось изменение интенсивности сигнала низкотемпературной фотолюминесценции (при 4.2 K) из более широкой квантовой ямы при совпадении кванта энергии лазера накачки с энергией экситонного перехода в узкой яме. Изменение положения максимума и интенсивности фотолюминисценции из более широкой квантовой ямы при возбуждении вблизи экситонных резонансов в узкой квантовой яме объясняется влиянием квантово-размерного эффекта Штарка на процесс экситонной рекомбинации.

Optical losses caused by the interaction of radiation with optically active Er3+ ions in epitaxial waveguide structures Si:Er/SOI have been directly measured. The cross section for the I-4(13/2)-> I-4(15/2) radiative transition in the Er3+ ion has been estimated as s300 K similar to 8 x 10(-19) cm(2) at T = 300 K and sigma(10 K) similar to 10(-17) cm(2) at T = 10 K.

Symmetrical and unsymmetrical 4,4′-biphenyl, and 9,10-anthracene derivatives with tris(trifluoromethyl)germylethynyl –CC–Ge(CF3)3 substitutes have been prepared, their properties have been studied and compared with those of dimethyl(phenyl)silylethynyl –CC–Si(Ph)Me2 compounds. UV–visible absorption, steady-state, and time-resolved fluorescence spectra in solution for this germanium and silicon compounds have been investigated. The process of photoinduced electron-transfer from the aromatic group to the germanium center has been found in the unsymmetrical 4-biphenyl –CC–Ge(CF3)3 molecule. Anthracene derivatives with –CC–Ge(CF3)3 substitutes have been characterized crystallographically.

The possibility of using the laser deposition method to grow crystalline light-emitting structures with GaAsSb/GaAs quantum wells (QWs) is experimentally demonstrated for the first time. The growth temperature of the GaAs1 − x Sb x layers is varied within the range 450–550°C; according to X-ray diffraction analyses, the content of antimony reaches x Sb ≈ 0.37 at a growth temperature of 450°C. Low-temperature (4 K) photoluminescence spectroscopy demonstrates the presence of a peak associated with the GaAsSb/GaAs QW at around 1.3 μm at the minimum laser-light pumping level. The optimal growth temperature T g = 500°C and arsine flow rate P A = 2.2 × 10−8 mol/s at which the best emission properties of QWs with x Sb ∼ 0.17–0.25 are observed at temperatures of 77 and 300 K are determined. It is shown that GaAsSb/GaAs QWs with similar parameters (width and composition) grown by laser deposition at 500°C and metal-organic vapor-phase epitaxy at 580°C have comparable optical quality.

Optical losses caused by the interaction of radiation with optically active Er3+ ions in epitaxial waveguide structures Si:Er/SOI have been directly measured. The cross section for the 4 I 13/2 → 4 I 15/2 radiative transition in the Er3+ ion has been estimated as σ300 K ∼ 8 × 10−19 cm2 at T = 300 K and σ10 K ∼ 10−17 cm2 at T = 10 K.

Optical losses caused by the interaction of radiation with optically active Er 3+ ions in epitaxial waveguide structures Si:Er/SOI have been directly measured. The cross section for the 4 I 13/2 → 4 I 15/2 radiative transition in the Er 3+ ion has been estimated as σ 300 K ∼ 8 × 10 −19 cm 2 at T = 300 K and σ 10 K ∼ 10 −17 cm 2 at T = 10 K.

The specific features of the nonradiative relaxation of Er3+ ions in Si:Er layers grown by sublimation molecular-beam epitaxy (SMBE) are studied. In Si:Er/Si diode structures containing precipitation-type emitting centers, a resonance photoresponse at the wavelength λ ≈ 1.5 μm is observed, which is indicative of the nonradiative relaxation of Er3+ ions via the energy back-transfer mechanism. Saturation of the erbium-related photocurrent is for the first time observed at high temperatures. This allows estimation of the concentration of Er centers that undergo relaxation via the above-mentioned back-transfer mechanism (N 0 ≈ 5 × 1016 cm−3). In terms of order of magnitude, the estimated concentration N 0 corresponds to the concentration of optically active Er ions upon excitation of the Si:Er layers by means of the recombination mechanism. The features of the nonradiative relaxation of Er3+ ions in Si:Er/Si structures with different types of emitting centers are analyzed.

In this work, a study of the photoluminescence (PL) temperature dependence in quantum well GaAs/GaAsSb and double quantum well InGaAs/GaAsSb/GaAs heterostructures grown by metalorganic chemical vapor deposition with different parameters of GaAsSb and InGaAs layers has been performed. It has been demonstrated that in double quantum well InGaAs/GaAsSb/GaAs heterostructures, a significant shift of the PL peak to a longer-wavelength region (up to 1.2 μm) and a considerable reduction in the PL thermal quenching in comparison with GaAs/GaAsSb structures can be obtained due to better localization of charge carriers in the double quantum well. For InGaAs/GaAsSb/GaAs heterostructures, an additional channel of radiative recombination with participation of the excited energy states in the quantum well, competing with the main ground-state radiative transition, has been revealed.

In this work, we report on the time-resolved photoluminescence studies of a double quantum well In0.2Ga0.8As/GaAs0.8Sb0.2/GaAs heterostructure which, in contrast to the GaAsSb/GaAs structures, is expected to provide effective confinement of electrons due to additional InGaAs layer. The studies at 4.2K have revealed a complicated nonmonotonic dependence of the ground-state transition energy on the concentration of nonequilibrium charge carriers in the quantum well. The effect observed in this work is important in terms of creating sources of radiation, including stimulated emission, on the basis of InGaAs/GaAsSb/GaAs structures. (C) 2014 AIP Publishing LLC.

The time-resolved photoluminescence of GaAs/AlGaAs quantum-cascade structures under intense pulse excitation is studied. Aside from optical transitions between the ground electron and hole states of a system of two tunnel-coupled quantum wells, the photoluminescence spectrum at short times after the excitation pulse exhibits features corresponding to transitions between the excited states of these wells, which are not observed in time-integrated photoluminescence spectra. It is shown that, due to a high pump level, the electron gas is initially strongly heated, which makes it possible to observe band-to-band transitions between both the ground and excited states. Nonequilibrium carriers cool down with a characteristic relaxation time of ∼125 ps.

A model of radiative and nonradiative transitions in silicon quantum dots is presented, which describes the photoluminescence temperature dependence of the ion-synthesized ensembles of Si nanocrystals in SiO2. A four-level system of transitions is considered that takes into account thermally activated processses and exchange splitting of the ground energy state of exciton in a silicon nanocrystal into triplet and singlet levels, the transfers from which to the ground state are responsible for the luminescence. The temperature dependence of monochromatic photoluminescence components was obtained based on the stationary solution of the system of kinetic equations for the population of levels that satisfactory describes the experimental data. The exciton energy splitting values depending on the energy of emitted photons were found and compared with the data in the literature.

A series of Pr, Nd, Ho, Er, Tm, and Yb complexes with 3-(2-benzoxazol-2-yl)-2-naphtholate and 3-(2-benzothiazol-2-yl)-2-naphtholate ligands was synthesized. The structure, as well as the photo- and electroluminescent properties of these complexes were studied. An extraordinary bright emission of Yb 3+ was detected. To explain the phenomenon, a novel excitation mechanism involving intramolecular electron transfer was proposed.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The spectral-kinetic properties of heterostructures with GaAs/GaAsSb-based and GaAsSb/InGaAs/GaAs-based quantum wells, emitting in the range of 1.0–1.2 μm are studied with picosecond and nanosecond temporal resolution. Intense photoluminescence in the GaAsSb/InGaAs/GaAs structure, as well as an increase in the photoluminescence wavelength by a factor of 2.5 and a shift of the location of the maximum of the peak (∼100 meV) to the longer-wavelength region were observed up to room temperature. It is established that as the molar fraction of Sb and the thickness of the InGaAs layer increase, the energy of the fundamental transition decreases by a factor of 140 meV compared with the GaAsSb/InGaAs/GaAs structure with a lower Sb content and a smaller thickness of the InGaAs layer. At 300 K, the emission wavelength of such a structure was 1.18 μm. In addition, an increase in the thickness of the InGaAs layer led to an increase in the room-temperature photoluminescence intensity by a factor of 60, which is associated with a decrease in the energy of the fundamental state for electrons in the InGaAs layer and, consequently, to larger electron localization and smaller temperature quenching of photoluminescence.