Circularly polarized light stimulation of spin transport in zinc-blende semiconductors

An experimental and theoretical study on the optically stimulated spin transport in zinc-blende semiconductors is presented. The first part of the paper describes an experiment which investigates the effect of a longitudinal electric field on the spin-polarized carriers induced by a circularly polarized light. Since the photo-generated hole spins relaxation is extremely fast, the experiment observes only the effect resulting from spin-polarized electrons accumulating at the transverse edges of the sample, as a result of left-right asymmetries in scattering for spin-up and spin-down electrons in the presence of spin–orbit (SO) interaction. It is found that the effect depends on the longitudinal electric field and doping density as well as on temperature. The results are discussed. The second part of the paper deals with a theoretical investigation using norm-conserving pseudopotential and Green function formalism to analyse the SO mechanism responsible for the light-induced Hall voltage. The findings resulting from the investigation are discussed and are compared with experimental data.     

Manifestation of up-conversion in Yb3+/Tm3+ doped Li2O–Y2O3–SiO2 glass system

In this study, we have investigated the principal role of Y₂O₃ on the emission features of Tm³⁺ ion and up-conversion phenomenon in Tm³⁺ and Yb³⁺ co-doped Li₂O–Y₂O₃–SiO₂ glass system. The concentration of Y₂O₃ is varied from 0 to 5 mol% while that of Yb³⁺ and Tm³⁺ is fixed. When the glasses are doped with Tm³⁺ ions, the intense blue and red emissions were observed, whereas Yb³⁺ doped glasses exhibited NIR emission at about 980 nm. When the glasses are co-doped with Tm³⁺ and Yb³⁺ ions and excited at 900 nm, the blue and red emission lines were observed to be reinforced and strengthened with increase in the concentration of Y₂O₃. The IR emission band detected at about 1.8 μm due to ³F₄ → ³H₆ transition of Tm³⁺ ions is also observed to be strengthened due to co-doping. The reasons for enhancement in the intensity of various emission bands due to co-doping have been identified and discussed with the help of rate equations for various emission transitions.     

Ordering behaviour of the mineral lawsonite

Lawsonite crystals have been investigated by dilatometry and dynamic mechanical analysis as well as by measurements of the optical birefringence and the dielectric constant in the temperature range 90K ≤T ≤ 633K. Two successive phase transitions have been found at low temperatures. The analysis of the spontaneous strain and the excess birefringence data reveals that the transition around 273 K (T ₁) is tricritical. The other transition around 120K. (T ₂) is of second order and proper ferroelectric. The mineral shows remarkable pretransitional effects in a temperature range up to 200 K. above T ₁. The data below T ₂ are interpreted in terms of a mutual interference of the two different ordering processes associated with T ₁ and T ₂, respectively.     

C_(60)-TTF及Ru-oligothienylacetylide复合物的设计合成:新型非线性光诱导效应纳米材料(英文)

Nonlinear optics has been the subject of intensive research because of its wide applications in field of photonics, nanophotonics[1] and optoelectroncs such as optical signal processing, broad-band optical communications, integrated optics, optical sensing, optical poling, optical limiting, optical computing etc.     

Ferrocene‐Donor and 4,5‐Dicyanoimidazole‐Acceptor Moieties in Charge‐Transfer Chromophores with π Linkers Tailored for Second‐Order Nonlinear Optics

A series of new nonlinear optical chromophores ( 1 – 15 ) that were comprised of ferrocene‐donor and 4,5‐dicyanoimidazole‐acceptor moieties and various π linkers of different length were synthesized. Support for the presence of significant D ? A interactions in these NLO‐phores was obtained from the evaluation of the quinoid character of the 1,4‐phenylene moieties and their electronic absorption spectra, which featured intense high‐energy (HE) bands that were accompanied by less‐intense low‐energy (LE) bands. The redox behavior of these compounds was investigated by cyclic voltammetry (CV) and by rotating‐disc voltammetry (RDV); their electrochemical gaps decreased steadily from 2.64 to 2.09 V. In addition to the experimentally obtained data, DFT calculations of their absorption spectra, HOMO/LUMO levels, and second‐order polarizabilities (β) (?2ω,ω,ω) were performed. A structure–property relationship study that was performed by systematically altering the π linker revealed that the intramolecular charge‐transfer and nonlinear optical properties of these inorganic–organic hybrid D? π? A systems ( 1 – 15 ) were primarily affected by: 1) The presence of olefinic/acetylenic subunits; 2) the length of the π linker; and 3) the spatial arrangement (planarity) of the π linker.     

Photoinduced effects in γ-glycine nanocrystallites embedded in polymer matrices

We have established a principal role of the polarity of polymer matrices on the piezooptical dispersion of the γ-glycine nanocrystallites embedded into the polymethymethacrylate (PMMA) and polycarbonate (PC) matrices. We found that the optical treatment by bicolor two laser beams at 1064 nm and 532 nm which are originating from the same 10 ns Nd:YAG laser, causes occurrence of the piezooptical effects. The optimal content of the γ-glycine nanocrystallites with respect to the magnitude of piezooptical coefficients was within the range of size 50-80 nm, corresponding to the 6.5 wt.%. We studied relaxation and spectral dependence of the corresponding coefficients of the piezooptic tensor.     

Photovoltaic response and values of state dipole moments in single-layered pyrazoloquinoline/polymer composites

We report the photovoltaic response of composite films formed by polymer transport matrices poly(3-octylthiophene) (P3OT) and poly(3-decylthiophene) (PDT) with incorporated 1H-pyrazolo[3,4-b]quinoline (PAQ) chromophore (see the first figure). The photovoltage (PV) data were obtained for different substituted PAQ possessing different state dipole moments. The photovoltaic cells were formed between ITO and aluminum electrodes. We found that the PV signal of polymer/PAQ substantially depends on the state dipole moments of the pyrazoloquinoline chromophore. This fact indicates on a possibility of significant enhancement of PV efficiency by appropriate variations of the state dipole moments of chromophore. This results in photoinduced electron transfer from polymer serving as donors to PAQ being the electron acceptor. Despite an efficiency of the PV devices is below 1%, however, it may be substantially enhanced in future varying the chromophore state dipole moments appropriately.     

UV-induced two-photon absorption in BiB3O6 single crystals

We show that BiB₃O₆ (BiBO) crystals, well known for their excellent second harmonic generation (SHG) properties, may also be of interest for third-order optical phenomena, particularly for two-photon absorption (TPA). Photoinduced TPA measurements were performed under illumination of excimer Xe–F laser (λ = 217 nm) as a photoinducing (pumping) beam. It created a thin surface layer (about 85 nm) that was a source of the observed photoinduced TPA. Raman shifted Nd-YAG laser radiation (λ = 1.9 μm) as well as its second and fourth harmonics (λ = 950 and λ = 475 nm, respectively) were used as fundamental (probing) beams of the TPA. The highest values of the TPA β coefficient were achieved for a polarization of the pumping light directed along crystallographic axis b. Quantum chemical simulations indicate on substantial contribution of UV-induced electron–phonon anharmonicity to the observed TPA. The obtained values of TPA coefficients indicate a possibility of using BiBO crystals as UV-operated optical limiters in a wide spectral range.     

Synthesis and Spectroscopic Study of Several Novel Annulated Azulene and Azafluoranthene Based Derivatives

A series of cyclized five-membered annulated azafluoranthene (AAF) and seven-membered annulated azulene (AA) derivatives have been synthesized and characterized by spectroscopic methods. The optical absorption and fluorescence spectra have been recorded in organic solvents of different polarity and analyzed within the semiempirical quantum chemical model PM3. In combination with the molecular dynamics simulations it properly reproduces the overall shape of the measured absorption spectra of both AA and AAF dyes including the strongest band in the region of 250-300 nm and the broad first absorption band above 400 nm. While the solvent polarity rises all the dyes exhibit the hypsochromic shift of the first absorption band and the bathochromic shift of the fluorescence band. Such opposite solvatochromic trends appear to be consistent with the Lippert-Mataga solvatochromic model. Compared to AA compounds, both AAF dyes reveal much stronger solvatochromic shift and broadening of the fluorescence band likewise the relative decrease in quantum yield on rising solvent polarity what may be an evidence for the intramolecular charge transfer mechanism being involved into the fluorescence emission. Depending on solvent polarity AA and AAF dyes emit light in the green-yellow range of the visible spectra what may be of interest for potential luminescent or electroluminescent applications.