Opto-electronics of non-fully conjugated molecules was demonstrated successfully in this research as light emitting diodes (LEDs). A series of benzoxazole poly[2,2-(m-2-hydroxyl phenylene)-4-4¡¦-hexafluoroisopro- pane-bibenzoxazoles] (6F-PBO-OH, Am) and benzimidazole poly[2,2¡¦- (2-hydroxy-o-phenylene)-5,5¡¦-bibenzimiazole] (OH-Pbi, B(1-m)) were copolymerized for coil-like non-fully conjugated poly-(Am-co-B(1-m)) for luminescence investigation. UV-Vis absorption of the non-fully conjugated copolymers showed superposition of individual absorption response from the two chemical components of the copolymer. However, the photoluminescence (PL) and the electroluminescence (EL) emissions had a red shift with increasing OH-Pbi content. It seemed to suggest that OH-Pbi was more charge delocalized than 6F-PBO-OH. In mono-layer LEDs, the diode threshold voltages were about at 2 ~ 3 V and the EL showed a green emission. Tunable emission was not observed in varying the m value of the copolymers. Composites of copolymer, poly(Am-co-B(1-m)) and multi-wall carbon nanotube (MWNT) were in-situ synthesized for mono-layer LED fabrication. Few MWNT aggregation was observed via the field-emission scanning electron microscopy. It was a success in dispersing MWNT in the copolymers. There was a red shift with MWNT addition in the PL and the EL emissions. The diode threshold voltages were about at 2 ~ 5 V and the EL emission still showed a green emission. According to this study, MWNT was inconsequential on the PL and the EL emissions of the copolymers up to 2 wt. %.

The focus of this study is mono-layer polymer light emitting diode (PLED). The emitting layer is poly-p-phenylenebenzobisoxazole (PBO). PBO is a fully conjugated heterocyclic aromatic rigid-rod polymer. Anode is indium-tin-oxide (ITO). Cathode is aluminum (Al). We used UV epoxy resin to package PLED devices, then measured current-voltage response, electroluminescence (EL) emission, and device lifetime. We demonstrate that the packaged mono-layer PBO LED reduced its demise from water and oxygen. Device lifetime increased from 1 hour to several hundred hours. At a larger bias voltage or current, emission intensity and device efficiency became higher. But decay rate increased leading to shortened device lifetime. Device temperature appeared linearly with current density. A red shift of the EL emission was observed. The £fmax. of emission spectra moved from 534 nm (initial) to 582 nm (after 100 hrs). After thermal annealing at 120¢J for ten hours, threshold voltage increased from 5 V to 12 V, current density decreased to several 10 mA/cm2, luminous intensity improved several ten times to 10-2 cd/m2, emission color changed from yellow-green to orange, luminous efficiency improved from 10-7 to 10-4 cd/A, but device lifetime declined to less than 20 hrs.

In this thesis, we study a series of Si doped InN films. These samples are grown on sapphire (0001) by molecular beam epitaxy (MBE). We have doped Si in InN films successfully. In this experiment, we control Si cell temperature to change carrier concentration of samples during InN film growth. The carrier concentration and mobility are explored by van der Pauw Hall measurement. As carrier concentration increases, mobility decreases. Carrier concentration changes with Si cell temperature from 6.16x1018 cm-3 to 1.19x1020 cm-3. Photoluminescence (PL) emission peak energy shows blue shift when carrier concentration increases, but the intensity decreases and full width at half maximum (FWHM) broadens. The PL peak of InN film with 1.19x1020 cm-3 split into two peaks 0.74 eV and 0.89 eV. In Raman spectra, Raman modes position and FWHM do not change with carrier concentration. In temperature dependence PL, the dependence of PL spectra shows decrease when carrier concentration increases. In power dependence PL, the PL emission peak energy of InN films with 6.16x1018 cm-3 and 8.50x1018 cm-3 show blue shift, while the PL peaks of InN films with 1.43x1019 cm-3 and 2.27x1019 cm-3 show no significant move. The fitting of power density vs. intensity is linear for all samples, but all slope of them are less than 1 expect for InN film with 1.43x1019 cm-3.

Luminescent emission of non-fully conjugated homopolymers was successfully demonstrated as light emitting diodes (LEDs) in this research. Coil-like heterocyclic aromatic poly[2,2-(2,5-dialkyloxyphenylene)-4-4¡¦-hexafluoroisopropanebibenzoxazo- les] (6F-PBO-CnOTpA, with n = 10, 15, and 20) was synthesized, and polymer composites of 6F-PBO-CnOTpA was in-situ synthesized with acidified multi-wall carbon nanotube (MWNT- COOH). The non-fully conjugated coil-like heterocyclic aromatic homopolymer was synthesized by reacting 2,2,bis-(3-amino-4-hydroxy[henyl]-hexafluoropropane with 2,5-dialkyloxyterephthalic acid (CnOTpA) for 6F-PBO-CnOTpA, with n = 10, 15, and 20. In addition, MWNT was acidified for connecting the carboxylic group (-COOH) to reduce its aspect ratio and entropy induced aggregation. MWNT-COOH was analyzed using elemental analysis (EA) and viscometry to validate the effects of acidification period. The EA result seemed to suggest that the oxygen content increased, and the carbon and the hydrogen contents decreased with acidification period. The inherent viscosity (£binh) decreased according to acidification period suggesting that the aspect ratio was indeed decreased. A hole transport layer of PEDOT¡GPSS was applied for multi-layer LEDs,. The LEDs all showed a threshold voltage about 4 V also for the composites of 6F-PBO-CnOTpA in-situ polymerized with MWNT-COOH. The 6F-PBO-CnOTpA LEDs with and without MWNT-COOH showed an electroluminescence emission range of 400 to 750 nm.

Poly-p-phenylenebenzobisoxazole (PBO) and carbon nanotube (CNT) contain fully conjugated rod like backbone entailing excellent mechanical properties, thermo -oxidative stability and solvent resistance. Rigid-rod PBO is commonly processed by dissolving in methanesulfonic acid or Lewis acid. A CNT of multi-wall carbon nanotube (MWNT) was dissolved in a Lewis acid solution of PBO for dispersion, and then spun for thin film. MWNT concentration in the films was from zero up to 5 wt. %. Compared to that of pure PBO film, all PBO/MWNT composite films retained same but enhanced UV-Vis absorption peaks, according to MWNT concentration, showing that PBO and MWNT did not have overlapping electron orbitals affecting their energy gaps. The composite films were excited at 325 nm using a He-Cd laser for photoluminescence (PL) emission. All PL spectra had maximum intensity at 540 nm indicative of yellow-green light emission. The composite films were fabricated as light emitting diodes using indium-tin-oxide/glass as substrate and anode, as well as vacuum evaporated Al as cathode for respectively hole and electron injectors. In these light emitting devices, MWNT doped PBO would decrease threshold voltage for about 2 V. Up to 0.1 wt. % of MWNT, the device emission current was increased two orders of magnitude than those of the devices without MWNT. Further increase of MWNT caused a successive decrease in electroluminescence emission intensity attributed to a quench effect from aggregations of MWNTs. UV epoxy resin was applied to package the mono-layer and bilayer PBO light emitting devices. The UV epoxy resin had some gas release during encapsulation. The devices were packaged with vacuum and without vacuum encapsulation. It was demonstrated that the device encapsulation reduced its demise from water and oxygen. The vacuum encapsulation could remove gaseous volatile of the device to inhibit oxygen and moisture to prolong device lifetime. The main degradation of light emitting device was the oxidization of cathode. The interactions between nitrogen of PBO and H2O caused the formation of hydrogen bonding at room temperature. Oxygen and moisture diffused into PBO polymer and were suspected to form mid-gap state for the polymer. The mid energy band disappeared upon heat treatment before encapsulation. A device under a higher bias voltage was found to have a shorter lifetime, but a larger EL emission intensity. The EL emission intensity was not a constant under a constant current bias. The vacuum encapsulated device had two or twenty times lifetime than, respectively, the device encapsulation without vacuum evacuation or in ambient conditions. The sandwich structure of ITO/PBO/Al had no observable photovoltaic effect due to insufficient exciton separation into electrons and holes. Poly(2,3-dihydro thieno-1,4-dioxin):polystyrenesulfonate (PEDOT:PSS), a hole transferring medium, was spun into a thin-film between PBO and indium-tin-oxide to facilitate photovoltaic (PV) effect by forming a donor-acceptor interlayer to separate and to transport photoinduced charges. Optimum PBO thickness for the PV heterojunctions was about 71 nm at which the hole transferring PEDOT:PSS generated the maximum short circuit current (Isc) at a thickness of 115 nm. By using a layer of lithium fluoride (LiF) as an electron transferring layer adhering to Al cathode, the most open circuit voltage (Voc) and the maximum short circuit current (Isc) were achieved with a LiF thickness of 1-2 nm due to possible electric dipole effect leading to an increase of Voc from 0.7 V to 0.92 V and of Isc from about 0.1

In this study, photoluminescence properties of as grown, Ge implanted GaSe and InSe crystals with doses 1013, 1014, and 1015 ions/cm2 and 1015 ions/cm2 Ge implanted and annealed GaSe and InSe single crystals grown by using 3-zone vertical Bridgman-Stockbarger system have been studied by photoluminescence spectroscopy (PL). PL spectra of as grown and implanted GaSe samples with three different doses have been studied in the ranges within the wavelength interval 570-850 nm and in the temperature ranges between 21 and 110 K. Temperature dependencies of all observed bands revealed that the peak with highest energy has excitonic origin and most of the others originate from donor-acceptor pair recombination. For GaSe samples implanted with 1013 and 1015 ions/cm2 Ge, PL spectra exhibited four emission bands while for as grown and the sample implanted with 1014 ions/cm2 v Ge had three bands. Variations of emission peaks were studied as a function of temperature. It was observed that centers of all bands shifted towards red continuously with temperature. The intensities of the emission peaks showed similarities with those obtained from as grown, 1013 and 1014 ions/cm2 Ge implanted GaSe while the peak intensities of the sample implanted with 1015 ions/cm2 Ge decreased with the temperature continuously. Using the temperature variation of the peak intensities and peak energy values activation energies were obtained and these results revealed that the two bands with low wavelength to be excitonic origin for the implanted samples with the doses 1013 and 1015 ions/cm2 Ge. Similar results were obtained for the implanted with 1015 ions/cm2 Ge and annealed sample. The other two peaks observed for these samples were attributed to donor acceptor pair transitions. In addition, direct band gaps were found to be 2.12 eV at 32 K for as grown, 2.121 eV at 25 K for 1013 ions/cm2 Ge implanted, 2.121 eV at 21 K for 1014 ions/cm2 Ge implanted, 2.124 eV at 33 K for 1015 ions/cm2 Ge implanted GaSe samples and lastly 2.113 eV at 28 K for 1015 ions/cm2 Ge implanted and annealed GaSe. PL spectra of as grown, 1013, 1014, 1015 ions/cm2 Ge implanted, and 1015 ion/cm2 Ge implanted and annealed InSe samples were also obtained at 20 K. Two broad bands were observed in the spectrum of all InSe crystals and considered to be due to impurity levels within the materials.

In this study, silicon (Si) rich silicon dioxide (SiO2) films and terbium (Tb) embedded in three different Si containing films has been produced by e-beam evaporation and magnetron sputtering techniques. Post deposition annealing was done for different temperatures and durations to study its effect on both Si nanocrystal formation and Tb luminescence. It was verified by X-ray diffraction technique (XRD) that Si nanocrystals were formed in Si rich matrices. Energy dispersive X-ray (EDS) spectroscopy analysis was carried out to determine the relative concentrations of the atoms inside the produced films. X-ray photoelectron spectroscopy (XPS) gave the evidence of different bonding structures inside the Tb-Si-O containing films. Depth profile measurements were carried out to analyze changes in the relative concentration during sputtering of the layers after annealing of the Tb containing film. Luminescence characteristics of Si nanocrystals and Tb3+ ions were studied by photoluminescence (PL) spectroscopy. It was observed that Tb3+ luminescence enhanced by an energy transfer from Si nanocrystals and trap levels in a matrix. This result supplies valuable information about the excitation paths of Tb3+ ion the way of intense luminescence.

In this thesis, in order to study the structural, optical and electrical transport properties of Tl2In2S3Se, TlInSeS and Tl2In2SSe3 crystals, X-ray diffraction (XRD), energy dispersive spectroscopic analysis (EDSA), transmission, reflection, photoluminescence (PL), thermally stimulated current (TSC) and photoconductivity decay (PC) measurements were carried out. Lattice parameters and atomic composition of these crystals were determined from XRD and EDSA experiments, respectively. By the help of transmission and reflection experiments, the room temperature absorption data were analyzed and it was revealed the coexistence of indirect and direct band gap energies of the studied crystals. Moreover, the refractive index dispersion parameters - oscillator energies, dispersion energies, oscillator strengths, oscillator wavelengths and zero-frequency refractive indexes were determined. Temperature-dependent transmission measurements made it possible to find the rate of change of indirect band gaps with temperature, absolute zero values of the band gap energies and Debye temperatures of these crystals. From the analysis of the transmission and reflection measurements, it was established that, there is a decrease in the values of indirect and direct band gaps energies and an increase in zero-frequency refractive indexes with increasing of selenium content. PL measurements were carried out to obtain the detailed information about recombination levels in crystals studied. The behavior of PL spectra were investigated as a function of laser excitation intensity and temperature. The variation of the spectra with laser excitation intensity and temperature suggested that the observed emission bands in these crystals were due to the donor-acceptor pair recombination. TSC measurements were carried out with various heating rates at different illumination temperatures to obtain information about trap levels in these crystals. The mean activation energies, attempt-to-escape frequencies, concentrations and capture cross sections of the traps were determined as a result of TSC spectra analysis. The analysis of experimental TSC curves registered at different light illumination temperatures revealed the exponential trap distribution in the studied crystals. From the analysis of PC measurements, carrier lifetimes were obtained.

Luminescence is the emission of light resulting from radiative transition of an atom from an excited state to a ground state. This radiative transition yields emission of photons and the luminescence is the general name which is used to classify &ldquo / cold emission&rdquo / other than the blackbody radiation. Spectroscopy involves the measurement of intensity of emitted, absorbed or scattered electromagnetic radiation as a function of wavelength. Thus, it is a valuable tool in the study of understanding the luminescence production mechanisms. Measurement of emission spectra gives information about the energy levels of transition and structure, geometry and composition of the sample. In this study, a versatile luminescence emission spectrometer was designed and developed with the main aim of measuring Photoluminescence (PL), Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) emission spectra of materials relevant for dosimetry. The spectrometer was constructed around a Littrow type monochromator by developing the necessary hardware, firmware and software. Wavelength calibration, measurement of spectral response and determination of resolution of the spectrometer were done using calibration lamps and a calibrated spectroradiometer. Finally the performance of the constructed spectrometer was tested by measuring the emission spectra of materials such as BeO, Al2O3 and CaF2 wherever possible the measured spectra were compared with the ones reported in the literature.

Molecular light emitting diode, including organic light emitting diode (OLED) and polymer light emitting diode (PLED), is commonly consist of one or several molecular layer(s) sandwiched between an anode and a cathode. When electrons and holes are injected respectively from cathode and anode into the molecular layer by a bias voltage, these two types of carriers migrate towards each other and a fraction of them recombine to form light emission. The focus of this study is electrode modifications of molecular light emitting diode. The electrode modifications include using a low work function cathode material, a high work function anode material or inserting a very thin electrode modifier between molecular layer and electrode for enhancing the electron or the hole injection efficiency leading to higher electroluminescence emission and/or lower threshold voltage. Low work function metal, Mg, could effectively reduce the electron injection barrier between molecular layer and cathode leading to better emission brightness and threshold voltage. A monolayer rigid-rod poly-p-phenylenebenzobisthiazole (PBT) or poly-p-phenylenebenzobis- oxazole (PBO) PLED with Mg cathode demonstrated a low threshold voltage of 3 V. Besides, a very thin layer of LiF (or Al2O3) inserted between molecular layer and Al cathode was applied to enhance the electron injection efficiency leading to a stronger electroluminescence intensity and a low threshold voltage of 2.8 V. On anode modification, a thin PBO layer was inserted between molecular layer and the indium-tin-oxide (ITO) substrate for improving the electroluminescence emission brightness and the threshold voltage. The PBO modified anode could effectively enhance the electro- luminescence intensity and lower the threshold voltage to 1 V~ 3 V on several mono- or multi-layer molecular light emitting diodes. Besides, a novel ITO substrate cleaning method via acid treatment was applied for increasing the work function of ITO to effectively enhance the hole injection efficiency.