Absorption spectra of poly-N-vinylcarbazole derivatives by experiment and simulation

Geometry molecular optimization and quantum chemical simulations of absorption spectra for newly synthesized poly-N-vinylcarbazole derivatives were performed using a semi-empirical approach. The studied polymers were modified by changing the positions of the carbazole group with respect to the polymer backbone. The absorption spectra were calculated for different numbers of PNVK monomers. A sufficient agreement between the calculated and experimentally measured spectra was observed. A change of the red shift absorption with respect to the blue shift was observed for cases when the number of monomers was higher than 4. The theoretical simulations indicate that this behavior is a consequence of the specific molecular structure of the considered molecules. The results demonstrate the potential of combined simulation and experimental studies in materials engineering and searching of new electro-luminescent materials

Microcrystalline Bi2ZnB2O7-polymer composites with silver nanoparticles as materials for laser operated devices

A novel type of composite for optoelectronic which is operated by second harmonic generation in the Bi2ZnB2O7 crystallites (with sizes varying within 1–30 μm) and Ag nanoparticles (NP) embedded in PMMA polymer composites is proposed. The substantial influence of the Ag NP on the bicolor induced second harmonic generation was established. The phototreatment was performed by bicolor beams of nanosecond Nd:YAG laser (1,064/532 nm) at angles between the fundamental and photoinducing beams varying within the 19°–21° range. The studies of the corresponding dependences of the SHG during illumination by the two coherent beams at 1,064/532 nm showed a maximal enhancement of the output SHG for the Ag NP average sizes equal to about 40 nm. The role of the excited plasmons may be here crucial. Additionally the time shift between the fundamental and the doubled frequency beam maxima was found, which shows strong sensitivity to illumination. The established time shift is sensitive to the pumping power

Дослідження оптичного поглинання та п’єзоелектричного ефекту у монокристалі твердого розчину AgGaGe3Se7.6Te0.4

In present work spectral distribution of absorption coefficient in the range of 100 – 300 K was investigated and band gap values  evaluated. Parameters of Urbach rule were calculated and linearity  of temperature dependence of Urbach energy was showed. Thermo induced piezoelectric effect in a range of 297 ‑ 357 K was investigated. Laser induced kinetics of piezomodule was investigated and absence of irreversible changes was showed. Influence of heating the crystal during laser illuminating on piezoelectric module was adjusted.У даній роботі досліджено спектральний розподіл коефіцієнта поглинання в діапазоні температур 100 – 300 К, оцінена ширина забороненої зони. Показана експоненційна залежність коефіцієнта поглинання в області краю поглинання, розраховані параметри правила Урбаха. Досліджено температурно- та лазерно- індукований п’єзоелектричний ефект. Скорегован

beta-BaTeMo2O9 microcrystals as promising optically operated materials

Studies of optical second harmonic generation (SHG) at fundamental wavelength of 1064 nm under photoinducing treatment of monoclinic piezoelectric beta-BaTeMo2O9 (beta-BTMO) were done. Continuous wave (CW) lasers generating at 808 and 1040 nm were used as photoinducing sources. The investigations were performed for the beta-BTMO microcrystalline powder samples with grain sizes varying within the 25-300 mu m range. We showed that depending on the microcrystallites size, the photoinduced changes of the SHG were substantially different depending on number of defects which were controlled by positron annihilation. The photoinduced SHG efficiency was substantially higher for more defective crystallites. The processes are completely reversible; however, their photoinduced time kinetics is very sensitive to the wavelength of the photoinducing CW laser beam. The possible reasons for the observed differences are discussed within a framework of intrinsic defect trapping levels and their interactions with phonon subsystem

Features of the alkynyl ruthenium chromophore with modified anionic subsystem UV absorption

Theoretical simulation of UV–vis absorption for a new series of alkynyl ruthenium chromophores spectra and investigations the influence of anionic substituence on a spectral shift of UV absorption was presented. The MM+ molecular force field method was used for total energy minimization and for building of the molecular optimized geometry [S.J. Weiner, P.A. Kollman, D.A. Case, U.C. Ghio, G. Alagona, J.S. Profeta, P. Weiner, J. Am. Chem. Soc. 106 (1984) 765; S.J. Weiner, P.A. Kollman, D.T. Nguyen, D.A. Case, J. Comput. Chem. 7 (1986) 230]. All quantum chemical calculations were performed by semi-empirical ZINDO/1 method within a framework of the restricted Hartree–Fock approach and convergence limit up to 10−6 eV after 500 iterations was achieved. Good agreement between the theoretically calculated and experimentally measured spectra was observed. The largest spectral shift in position of absorption peaks was observed for compound containing the anionic (Cl), substituent. The theoretically calculated absorption maximum is blue shifted with respect to the experimental spectra for all compounds what is connected with the changes of the charge transfer determining the corresponding state dipole moments. Analysis of the theoretical spectra shows a substantial sensitivity to the backside groups

Linear and nonlinear optical properties of ZnO/PMMA nanocomposite films

The nanoscale crystals (NCs) of ZnO were embedded into polymethylmethacrylate (PMMA) polymeric matrix and nanocomposite films were prepared by modified spin coating method. The surface of the ZnO/PMMA nanocomposite films has been investigated using atomic force and scanning electron microscopy. The prepared films are highly transparent, the ultraviolet-visible spectra show their high optical quality. The second and third harmonic generation (SHG and THG) studies of ZnO/PMMA nanocomposite films with different concentrations of ZnO NCs were carried out at λ=1.064 μm and the effective values of the second and third order nonlinear susceptibilities were estimated to be higher than that of ZnO bulk for the films at low concentration of ZnO NCs. This could indicate that surface effects in ZnO/PMMA nanocomposite films have a dominant role over bulk effects for the SHG and THG processes

Physical, structural, thermal, and optical spectroscopy studies of TeO2–B2O3–MoO3–ZnO–R2O (R = Li, Na, and K)/MO (M = Mg, Ca, and Pb) glasses

Six optically transparent zinc molybdenum borotellurite glasses containing different network modifier ions (alkali, alkaline, and heavy metal oxides) with compositions, 60TeO2–10B2O3–10MoO3–10ZnO–10M (mol%) (M = Li2O, Na2O, K2O, MgO, CaO, and PbO) were prepared by melt quenching technique. For all these glass matrices, physical, structural, thermal, and optical properties have been studied. The physical properties of all the glasses were evaluated with respect to the glass composition. The structure of the glasses was monitored by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Energy dispersive X-ray analysis (EDAX), Attenuated total reflectance-Fourier transform infrared (ATR-FTIR), and Raman spectroscopy. The XRD and SEM measurements reveal the amorphous nature for all the prepared glasses and EDAX confirms that all the elements present in the respective glasses. The presence of various functional groups such as stretching vibrations of the TeO4 trigonal bi-pyramid structure, asymmetrical stretching vibrations of the TeO3 trigonal structural units, B–O bond stretching in BO4 groups, asymmetric stretching vibrations of B––O bond in trigonal BO3 units from various types of borate groups, stretching vibrations of Mo–O–Mo linkages, corner shared MoO6 octahedra units, stretching vibrations of Mo–O− bonds in MoO6 units, including stretching vibrations of ZnO4− structural units, and non-hygroscopic nature of the glasses are confirmed by ATR-FTIR and Raman spectra, respectively. It is established that the glass network is primarily a mixture of TeO4, TeO3/TeO3+1 and BO4, BO3 structural units. The thermal properties of the glasses were obtained by performing simultaneous thermal analysis (STA). For these glasses, from the differential scanning calorimetry (DSC) profiles the glass transition temperature (Tg), onset crystallization temperature (Tx), crystallization temperature (Tc), and melting temperature (Tm) are identified and from these values, all relevant thermal parameters were evaluated to obtain complete thermal behavior of the synthesized glasses. The calculated thermal stability values have been varied in the temperature range of 106–189 °C with different modifier ions incorporation. For alkali metal oxides incorporated glasses reduced glass transition temperature (Trg) values almost coincide with classical two-third rule while alkaline and heavy metal oxides based glasses weakly obey this rule in our study of relationship between glass transition temperature (Tg) and melting temperature (Tm). From the measured optical absorption spectra of all the glasses, direct and indirect optical band gap energies were evaluated and the values of indirect optical band gap energies calculated from absorption spectra (Eopt) match well with the values of optical band gap energies calculated from absorption spectrum fitting (ASF) method. The optical absorption cut-off wavelengths have shown a gradual spectral red shift from Li to Pb oxides based glass compositions indicating the decrease of rigidity of the glasses. Optical band gap energies were calculated to be within the range of 2.325–2.655 eV for direct and 1.790–2.378 eV for indirect transitions and both direct and indirect band gap values decreases monotonically from Li to Pb oxides introduced glass. The structural, thermal, and optical features of all the synthesized tellurite rich glasses with different modifier ions are understood and our comprehensive analysis could contribute towards the development of suitable fiber Raman amplifiers

Synthesis and Characterization of Glomerate GaN Nanowires

Glomerate GaN nanowires were synthesized on Si(111) substrates by annealing sputtered Ga2O3/Co films under flowing ammonia at temperature of 950 °C. X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy and Fourier transformed infrared spectra were used to characterize the morphology, crystallinity and microstructure of the as-synthesized samples. Our results show that the samples are of hexagonal wurtzite structure. For the majority of GaN nanowires, the length is up to tens of microns and the diameter is in the range of 50–200 nm. The growth process of the GaN nanowires is dominated by Co–Ga–N alloy mechanism

Contribution of hexagonal-like structure to the nonlinear optics in large sized SiC nanocrystallites

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