Iu. Nistor’s research while affiliated with Academy of Sciences of Moldova and other places

Nanocomposites (NCs) thin films based on oligomer poly-N-epoxypropylcarbazole (PEPC) and organic coordinated compounds (OCC) have been obtained by chemical methods. Absorption threshold for samples with different concentrations was determined as 3.34 - 3.4 eV. Photoluminescence spectra reveal a number of emission bands centered at 580, 590, 612-615, 651, and 700 nm, which can be associated to internal 4f - 4f transitions of Eu3+ ion 5D0 → 7Fi (i = 0,1,2,3 and 4). By comparing the photoluminescence spectra of the organic compound and of the PEPC/Eu(o- MBA)3Phen nanocomposite one can observe the amplification of the photoluminescence intensity in NC.

We present experimental results on copolymer-based nanocomposite made of styrene with butyl methacrylate (SBMA) (1:1) and inorganic semiconductor CdS. Thin film composite samples have been characterized by UV-Vis absorption and photoluminescent spectroscopy, as well as by transmission electron microscopy. Transmission electron microscope (TEM) examination confirms a relatively narrow distribution of CdS nanoclusters in the SBMA matrix, which covers the range 2-10 nm. On the other side, the average CdS particles size estimated from the position of first excitonic peak in the UV-Vis absorption spectrum was found to be 2.8 nm and 4.4 nm for two samples with different duration of thermal treatment, which is in good agreement with photoluminescence (PL) experimental data. The PL spectrum for CdS nanocrystals is dominated by near-band-edge emission. The relatively narrow line width (40-45 nm) of the main PL band suggests the nanoparticles having narrow size distribution. On the other side, relatively low PL emission from surface trap states at longer wavelengths were observed in the region 500-750 nm indicating on recombination on defects. Key words: nanocomposite, polymer matrix, photoluminescence,.

A fiber optic intrusion monitoring system comprises a multimode optical fiber, a coherent light source, a CCD, and a processor for generation of the output signal. The system is based on the principle of variation of speckle pattern in the far-field of a multimode optical fiber under mechanical perturbation. By processing the speckle pattern, one can derive information on the amplitude of perturbation. The algorithm for processing of the speckle pattern is based on comparison of the current speckle image with the reference image. An intrusion monitoring system can be applied in surveillance of perimeters, industrial objects, deposits of chemicals and radioactive waste, etc.

Polymer fluorescent nanocomposite materials are of interest for practical applications as well as from the point of view of understanding the mechanisms of carrier transport, energy transfer, recombination and luminescence. We present here experimental results on polymer-based nanocomposite material made of styrene with butyl methacrylate (SBMA) (1:1), isothiocyanato-chalcone (ITCC) and inorganic semiconductor CdS. The concentration of CdS semiconductor nanoparticles was varied in the range 0–20%. Thin film composite samples have been characterized by UV-VIS absorption, photoluminescence spectroscopy, X-ray diffraction, and atomic force microscopy (AFM). Examination of thin films by AFM shows that the surface of the composite can be described as quasi-ordered structure consisting of conic-shaped elements with 25–50 nm height. The average CdS particle size estimated from the X-ray diffraction pattern correlates with the corresponding value obtained from the UV-VIS absorption spectrum, and it was found to vary in the range from 9 to 17 nm. The PL emission spectra have been registered at room temperature. The nanocomposite samples exhibit a strong photoluminescence (PL) band in the range 400–650 nm under the excitation of UV nitrogen laser beam = 337 nm, with the PL maximum varying slightly in dependence of the concentration of CdS nanoparticles. The observed luminescence is supposed to originate from the radiative recombination involving various donor and acceptor centers.

A high sensitivity speckle based fiber-optic method for registration of low intensity IR radiation is described. The method is based on the effect of variation of the speckle pattern in the far-field of a multimode fiber. IR radiation that falls on a lateral surface of the fiber leads to variation of the speckle image. Computer processing of the speckle image provides information on the amplitude of perturbation that interacts with the fiber. An algorithm was developed for processing of the speckle image and determining of the intensity of IR radiation. The results of the computer simulation correlate well with the experimental ones.

A high sensitivity fiber-optic method for registration of low intensity IR radiation is proposed. The method is based on the effect of variation of the speckle pattern in the far-field of a multimode fiber. IR radiation that falls on a lateral surface of the fiber leads to variation of the speckle image. Computer processing of the speckle image provides information on the amplitude of the perturbation that hits the fiber. An algorithm has been developed for processing of the speckle image and determining of the intensity of IR radiation. The results of computer simulation correlate sufficiently well with experimental ones.

A high sensitivity speckle based fiber-optic method for registration of low intensity IR radiation is proposed. The method is based on the effect of variation of the speckle pattern in the far-field of a multimode fiber. IR radiation that falls on a lateral surface of the fiber leads to variation of the speckle image. Computer processing of the speckle image provides information on the amplitude of the perturbation that hits the fiber. An algorithm has been developed for processing of the speckle image and determining of the intensity of IR radiation. The results of computer simulation correlate sufficiently well with experimental ones.

A high sensitivity fiber-optic method for registration of infrared (IR) radiation is proposed. The method is based on the effect of modal interference in an optical fiber. The speckle pattern is registered in the far field of a multimode fiber and is processed by a PC for deriving the output signal. The method also can be applied for registration of temperature, mechanical vibrations, etc.

Chalcogenide glasses are promising materials for different applications in integrated and fiber optics due to a number of advantages in comparison to other optical materials. Chalcogenide glasses exhibit excellent transmission in the near and infrared spectral region up to ~12 µm, high refractive index (n≥2.4), low phonon energy, and higher nonlinearity of the refractive index in respect to silica (typically x100) [1-2]. One of interesting features of chalcogenide glasses is the effect of reversible photoinduced absorption (PA) observed when the chalcogenide glass is illuminated with bandgap light (hν exc ~ E g). Photoinduced absorption proved to be an efficient tool for investigation of optical properties in amorphous semiconductor materials [3-6]. PA effect presents interest both as a method for determination of phenomenological parameters of localized states in chalcogenide glasses as well as from the point of view of application in optoelectronics. 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 1 2 3 4 5 6 W eak absorption tail Urbach tail 2 1 ln(α, dB/m) hν, eV Fig.1. The spectral distribution of the optical absorption in chalcogenide fibers As 2 S 3 (1) and As-S-Se (2). We have investigated the photoinduced absorption in As 2 S 3 glass fibers under continuos illumination of the lateral surface of the fibers with band-gap light. The spectral distribution of the optical absorption in chalcogenide glass fibers As 2 S 3 is represented in Fig.1. PA meas-urements have been carried out on unclad fibre samples in the temperature range 77-330 K. The power of the probe beam was adjusted so that its intensity was much less than the inten-sity of the excitation light not to affect the magnitude of photoinduced absorption. We note that after secession of the bandgap light a full restoration of initial transmittance occurs. Dif-ferent lengths of the fibre samples (up to 4 m) have been used for measurement of PA coeffi-cient.