The development of ultraviolet semiconductor emitters (LEDs and lasers) will enable a large number of industrial and medical applications. AlGaN alloys are ideally suited for the development of such devices since their energy gap can be tuned from the near UV (365 nm) to deep UV (200 nm). However, the doping of such materials n- and p-type is difficult. Another problem is the generally poor light extraction efficiency from both UV and visible LEDs. This research addressed the first problem by developing UV emitters in the form of graded-index-separate-confinement-heterostructure (GRINSCH). In these device the active region is embedded in two compositionally graded wave guiding layers. Due to the polar nature of nitride semiconductors these compositionally graded AlGaN films are doped p- or n-type if the grading changes from high to low concentration or from low to high concentration respectively. Thus, a p-n junction is automatically formed without the incorporation of dopants. The polarization induced doping level in these structures was calculated to be 1018cm-3 for the p- and n-sides. A number of devices, whose active region is either 75 nm Al0.72Ga0.28N bulk film or multiple QWs have been grown on 6H-SiC substrates by Molecular-Beam Epitaxy (MBE) and investigated. The emission properties of these structures were investigated by cathodoluminescence (CL) and by measuring their optical gain. A maximum net modal gain in excess of 80 cm-1 was measured with an optical gain threshold of 14 µJ / cm2. Some of these structures, emitting in the near UV, were also electrically pumped. The second problem was addressed by incorporating dielectric (TiO2) photonic crystals on the phosphor plates of white LEDs in order to increase the light extraction efficiency upon illumination with blue LEDs. The two-dimensional (2D) hexagonal-lattice of TiO2 photonic crystal was formed by e-beam lithography on low-scattering (Y1-xCex)3Al5O12 (YAG:Ce) ceramic phosphor plates. Yellow light extraction enhancement by a factor of 4.4 was achieved with a 2D photonic crystal nano-cylinders having diameter 430 nm, lattice constant of 580 nm and height of 350 nm. Simulations using a three-dimensional finite difference time domain are consistent with our measured data.

Orientador: Dante Luis Chinaglia / Banca: Gerson Santarine / Banca: Valtencir Zucolloto / Resumo: As novas tecnologias para a construção de telas e displays têm permitido reduzir o consumo de energia, o peso e a espessura, como também melhorar a eficiência e flexibilidade se comparado aos antigos monitores de CRTs e até mesmo aos atuais displays de cristal líquido. Dentre estas novas tecnologias destacam-se as que utilizam materiais orgânicos (OLED) ou orgânicos poliméricos (PLED) não somente por suas possibilidades de aplicações industriais, mas também por permitirem o desenvolvimento das ciências básica e aplicada. Seguindo uma linha alternativa, propomos, neste trabalho, um novo compósito híbrido, resultante da combinação de uma fase polimérica e uma fase inorgânica, que, do nosso ponto de vista também poderá contribuir para o desenvolvimento dessa nova geração de displays e telas. Este compósito é formado pela blenda de um polímero condutor dopado, a PANI (polianilina) ou POMA (poli(o-metóxi anilina)), e um polímero isolante, o P(VDF-TrFE) poli(vinilideno-co-trifluoretileno), na qual micro partículas de Zn2SiO4:Mn (SZF) foram adicionadas. Para o desenvolvimento desse novo compósito, estudamos cada um de seus elementos constituintes, notadamente quanto ao seu modo de preparo, características morfológicas e propriedades elétricas. Como resultado final, obtivemos dispositivos constituídos de uma única camada do compósito híbrido depositado por espalhamento sobre um substrato de ITO/FTO, acrescido, ainda, de um eletrodo de alumínio depositado por evaporação. Para a caracterização destes dispositivos foram realizadas medidas de condutividade elétrica, luminescência (L) e fotoluminescência (PL). Os compósitos PANI/P(VDF-TrFE)/SZF 05/95/80 e POMA/P(VDF-TrFE)/SZF 25/75/80 com condutividade elétrica da ordem de 10-3 S/m foram os que melhor se adequaram para a construção dos dispositivos. Os espectros de L e PL apresentaram um pico em ? = 538... (Resumo completo, clicar acesso eletrônico abaixo). / Abstract: New technologies recently applied to the fabrication of organic screens and displays have allowed the manufacture of lighter, thinner monitors in comparison to either the conventional cathodic rays tube (CRTs) or the liquid crystal displays (LCDs). In addition, displays based on organic materials (the so-called organic light emitting displays (OLEDs and the polymeric light emitting displays - PLEDs) may exhibit improved efficiency and flexibility. The organic displays have attracted attention of a number of research groups aimed at investigating the potential applications of these new devices in the electronic industry. In this study, a new hybrid composite comprising an inorganic phase dispersed in a polymeric matrix was investigated as a possible candidate material for displays fabrication. The continuous, organic phase was a blend containing a conducting polymer, viz. polyaniline (PANI) or its derivative poly(o-methoxyaniline) (POMA) and an insulating polymer, P(VDF-TrFE) (Poly(viny1idene fluoride- trifluorethylene)). Micro particles of Zn2SiO4:Mn (SZF) was added to the polymeric phase as the luminescent, active material. Luminescent devices were fabricating using a conventional trilayer architecture in which a thin film of the hybrid composite was deposited between two conducting electrodes. As the anode electrode we used either Indium-TinOxide (ITO) or Fluorine-Tin-Oxide (FTO)-covered glass plates. Evaporated aluminum was used as the cathode electrode. The material/device characterization was carried out using electric conductivity, luminescence (L) and photoluminescence (PL) measurements. PANI/P(VDFTrFE)/ SZF (05/95)/80 and POMA/P(VDF-TrFE)/SZF (25/75)/80 composites compositions presented the best performance, with electric conductivity of ca. 10-3 S/m. Luminescence and photoluminescence measurements revealed that both devices exhibited an emission band centered at 538 nm... (Complete abstract, click electronic address below). / Mestre

This thesis is about new ways to experimentally realise materials with desired nano-structures for solution-processable optoelectronic devices such as solar cells and light-emitting diodes (LEDs), and examine structure-performance relationships in these devices. Short exciton diffusion length limits the efficiency of most exciton-based solar cells. By introducing nano-structured architectures to solar cells, excitons can be separated more effectively, leading to an enhancement of the cell’s power conversion efficiency. We use diblock copolymer lithography combined with solvent-vapour-assisted imprinting to fabricate nano-structures with 20-80 nm feature sizes. We demonstrate nanostructured solar cell incorporating the high-performance polymer PBDTTT-CT. Furthermore, we demonstrated the patterning of singlet fission materials, including a TIPS-pentacene solar cell based on ZnO nanopillars. Recently perovskites have emerged as a promising semiconductor for optoelectronic applications. We demonstrate a perovskite light-emitting diode that employs perovskite nanoparticles embedded in a dielectric polymer matrix as the emissive layer. The emissive layer is spin-coated from perovskite precursor/polymer blend solution. The resultant polymer-perovskite composites effectively block shunt pathways within the LED, thus leading to an external quantum efficiency of 1.2%, one order of magnitude higher than previous reports. We demonstrate formations of stably emissive perovskite nanoparticles in an alumina nanoparticle matrix. These nanoparticles have much higher photoluminescence quantum efficiency (25%) than bulk perovskite and the emission is found to be stable over several months. Finally, we demonstrate a new vapour-phase crosslinking method to construct full-colour perovskite nanocrystal LEDs. With detailed structural and compositional analysis we are able to pinpoint the aluminium-based crosslinker that resides between the nanocrystals, which enables remarkably high EQE of 5.7% in CsPbI3 LEDs.

In recent years there is growing research in optical wireless communication. This growing popularity isdue to several characteristics like such as large bandwidth that is also not having spectrum regulationsimposed, low cost and license-free operation. Since visible light communications (VLC) is a branch ofoptical wave communications (OWC), it is used for replacing RF communications. The other primaryreason for the use of visible light communications [1], because it uses 400 THz of unlicensed secure andradio free media for wireless communications which are 1000 times more than that of radiocommunications. For transmission of VLC, we use LED as light sources.Due to the high efficiency and less power consumption LED have replaced the oldfluorescence lamps, LED provide the dual functionality they can provide lighting and can providecommunications (transfer of data) just like Wi-Fi. In LED the on and off state is so fast that the humaneye can’t even perceive it. The on and off state can be taken as 1 and 0’s and through this we can transferthe data, this type of modulation is called OOK keying modulation it is used for single carrier modulationscheme. We can interpret the data that is received from the transceiver side with the help of thephotodiode at the receiver’s side. This communication technique can provide better security as there is nointerference, as light can't penetrate through walls leaving the data transfer to the room itself. ThroughVLC we can offer better security to data over RF communications.In this thesis, the implementation process has been performed in MATLABsimulations where we analyse different modulation techniques and parameters. We design a room withdimensions as 5m*5m*3m as length, width and height. We take multiple LED’s at the top and determinethe illumination parameters in the room due to the light emitted from the LED. The receiver is located ona desk and we calculate the number of data rates received at the receiver. The modulation techniques usedin this thesis are OOK keying modulation. We estimate the data rates in two methodologies directdetection (Line of sight) and also, we take reflections from the wall into consideration (Non-line of sight).The effect of data rates due to illumination and distance are also determined. In this thesis we transfer dataover the transmitter and receive the information at the receiver for obtained information the calculation of bit error rate (BER) is performed for both single LED and multiple LED array. The analysis is performed between the performance metrics of a single LED’s and multiple LED’s arrays to determine better-LEDarray.Key Words: OOK modulation scheme, MATLAB-Simulation, Light Emitting Diodes .

abstract: Group III-nitride semiconductors have been commercially used in the fabrication of light-emitting diodes and laser diodes, covering the ultraviolet-visible-infrared spectral range and exhibit unique properties suitable for modern optoelectronic applications. InGaN ternary alloys have energy band gaps ranging from 0.7 to 3.4 eV. It has a great potential in the application for high efficient solar cells. AlGaN ternary alloys have energy band gaps ranging from 3.4 to 6.2 eV. These alloys have a great potential in the application of deep ultra violet laser diodes. However, there are still many issues with these materials that remain to be solved. In this dissertation, several issues concerning structural, electronic, and optical properties of III-nitrides have been investigated using transmission electron microscopy. First, the microstructure of In_xGa_1-xN (<italic>x</italic> = 0.22, 0.46, 0.60, and 0.67) films grown by metal-modulated epitaxy on GaN buffer /sapphire substrates is studied. The effect of indium composition on the structure of InGaN films and strain relaxation is carefully analyzed. High luminescence intensity, low defect density, and uniform full misfit strain relaxation are observed for <italic>x</italic> = 0.67. Second, the properties of high-indium-content InGaN thin films using a new molecular beam epitaxy method have been studied for applications in solar cell technologies. This method uses a high quality AlN buffer with large lattice mismatch that results in a critical thickness below one lattice parameter. Finally, the effect of different substrates and number of gallium sources on the microstructure of AlGaN-based deep ultraviolet laser has been studied. It is found that defects in epitaxial layer are greatly reduced when the structure is deposited on a single crystal AlN substrate. Two gallium sources in the growth of multiple quantum wells active region are found to cause a significant improvement in the quality of quantum well structures. / Dissertation/Thesis / Doctoral Dissertation Physics 2014

abstract: Research and development of organic materials and devices for electronic applications has become an increasingly active area. Display and solid-state lighting are the most mature applications and, and products have been commercially available for several years as of this writing. Significant efforts also focus on materials for organic photovoltaic applications. Some of the newest work is in devices for medical, sensor and prosthetic applications. Worldwide energy demand is increasing as the population grows and the standard of living in developing countries improves. Some studies estimate as much as 20% of annual energy usage is consumed by lighting. Improvements are being made in lightweight, flexible, rugged panels that use organic light emitting diodes (OLEDs), which are particularly useful in developing regions with limited energy availability and harsh environments. Displays also benefit from more efficient materials as well as the lighter weight and ruggedness enabled by flexible substrates. Displays may require different emission characteristics compared with solid-state lighting. Some display technologies use a white OLED (WOLED) backlight with a color filter, but these are more complex and less efficient than displays that use separate emissive materials that produce the saturated colors needed to reproduce the entire color gamut. Saturated colors require narrow-band emitters. Full-color OLED displays up to and including television size are now commercially available from several suppliers, but research continues to develop more efficient and more stable materials. This research program investigates several topics relevant to solid-state lighting and display applications. One project is development of a device structure to optimize performance of a new stable Pt-based red emitter developed in Prof Jian Li's group. Another project investigates new Pt-based red, green and blue emitters for lighting applications and compares a red/blue structure with a red/green/blue structure to produce light with high color rendering index. Another part of this work describes the fabrication of a 14.7" diagonal full color active-matrix OLED display on plastic substrate. The backplanes were designed and fabricated in the ASU Flexible Display Center and required significant engineering to develop; a discussion of that process is also included. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2017

The molecular design, synthesis, spectroscopic and photophysical characterization of a series of cyanostilbene-based compounds are studied in this thesis. The thermal, electrochemical and aggregation induced emission (AIE) properties of these cyanostilbene-based compounds, as well as their application in organic lighting-emitting diodes, live cell imaging, chemical vapor sensor were investigated. Chapter 1 gives a brief introduction on the aggregation-caused quenching (ACQ) behavior of the conventional organic luminogens and the discovery and proposed mechanism of AIE phenomenon. Furthermore, some examples and the applications of these AIE compounds will be discussed. In Chapter 2, triphenylamine- and carbazole-containing cyanostilbene-based derivatives are presented. From the examination of the emission profile, they are all AIE-active through comparison of the photoluminescence intensity in dissolved and in aggregated states. Additionally, the calculation of the enhancement ratio (I/I0 – 1) of each fluorophore was performed in order to quantify its AIE effect. One of our cyanostilbene-based luminogens has achieved an enhancement ratio with a value of 1128. This cyanostilbene-based luminogens has also shown good performance in OLED investigation. In addition to the OLEDs application, the selected cyanostilbene-based luminogens with solid-state emission, cell-permeability and reversible switch-on/off capability have illustrated the positive result in live-cell imaging and chemical vapor sensing. Conjugated polymer with high molecular weight is the superior option by overcoming the weaknesses of low-molecular-weight luminogens with excellent thin-film form ability and comparatively simple and inexpensive fabrication processes. The design and synthesis of the cyanostilbene-based polymeric chromophores are described in Chapter 3. The polymerization of the AIE-active diacetylene ligands by connection of trans-[Pt(PBu3)2] unit at both ends has successfully retained their AIE behavior. In contrast, the ACQ problem has occurred on the polymers with organic spacers and the AIE-active ligands. From the DFT calculation on the Pt polymers and the blue shift of emission spectra in high water content suggested that the AIE phenomenon of Pt polymers is probably originated from the elimination of the non-radiative intramolecular charge transfer (ICT) process. Owing to the high demand in red-emitting materials in the applications of electroluminescent devices, fluorescent sensing and bio-imaging, effort has been made to design a system with the new chromophores with donor (D) – acceptor (A) system and thus to synthesize phenothiazine (D)-containing cyanostilbene (A)-based derivatives which are depicted in Chapter 4. Consistent with the conventional AIE-active luminogens with a successively climb of photoluminescence intensities in response to the increase of water proportion, phenothiazine-containing cyanostilbene-based derivatives has exhibited a V-shape fashion of emission intensity. It suggests that the emission of chromophores started to be quenched due to the increase of solvent polarity, overriding that of the molecular aggregation when a “small” volume of water is being introduced. While aggregate formation was dominant from the addition of a “large” amount of poor solvent, less polar local environment was created which suppressed the non-radiative transition to the ICT state and intensified the emission efficiency. Phenothiazine (D) – cyanostilbene (A) system has created a series of red-emitting chromophores with great tunability for the sake of achieving the desired emission color and better emission efficiency. To functionalize these AIE-active cyanostilbene-based chromophores, pyridine group was attached to the compounds to take the advantage of its metal-chelating capability, which is discussed in Chapter 5. The AIE features of cyanostilbene-based compounds can be preserved after the introduction of the pyridyl unit. Even it possessed a weak photoluminescence in its dilute solution which suggest that the high electron delocalization within the molecule has rigidified the structure to some extent, it is transformed to a highly emissive state with a high proportion of water. The exclusive variation of emission behavior with obvious bathochromic shift and boost of emission spectrum in the presence of cadmium-(II) ion has demonstrated its potential metal ion sensing ability. Chapter 6 and 7 present the concluding remarks and the experimental data of the compounds of Chapter 2 to 5, respectively.

Cette thèse porte sur l'élaboration de dispositifs d'émission et de photodétection à base de nanocristaux colloïdaux dans le visible et le proche infrarouge. Dans un premier temps, nous avons développé des dispositifs lumineux à base de nanocristaux de CdSe/ZnS émettant dans le rouge-orange. Pour cela, nous avons tout d'abord travaillé en déposant des polymères par voie liquide, des nanocristaux par différentes techniques humides ou sèches et enfin des petites molécules par évaporation. Ensuite, dans un but d'optimisation des performances de nos dispositifs, nous avons développé une technique originale de dépôt des QDs, que nous avons appelée Langmuir Schaeffer Stamping (LSS). Cette technique de dépôt économique en matériaux et homogène permet de travailler uniquement avec un empilement de films minces déposés par évaporation des petites molécules, et permet une nette augmentation de l'efficacité des composants. Nous avons étudié les mécanismes à l'origine de l'électroluminescence, dans nos dispositifs c'est l'injection directe qui prédomine. Enfin, en travaillant à l'aide de nanocristaux de PbS, nous avons développé des photodétecteurs pour le proche infrarouge de détectivité 109Jones. Des sources QDLEDs infrarouges à base de nanocristaux de PbS ont également été élaborées. / This work is devoted to the development of Visible and Near-Infrared Light Emitting Diodes and photodetectors based on colloidal nanocrystals. First, we report a wet strategy for solution processed QDLEDs. Using spin coated and inkjet printed polymers, we have developed our first devices. Unfortunately, their efficiencies were quite low. To overcome these issues, we have developed an original QDs deposition method based on stamping and Langmuir processes, called Langmuir-Schaeffer Stamping (LSS). LSS is a very cost-efficient, dry, simple and homogeneous method to deposit nanocrystals on any substrate, even on small molecules deposited layers. Using LSS, we have developed efficient devices whose specifications are reported here. Direct injection and Förster mechanisms are studied. Furthermore we have fabricated infrared devices with PbS nanocrystals. Performances of our 109 Jones NIR photo-detectors and NIR-QDLEDs are presented in this thesis.

Made available in DSpace on 2014-10-09T12:49:25Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:26Z (GMT). No. of bitstreams: 1 10196.pdf: 3238659 bytes, checksum: f29ba4edf822c7281b6254e30d189680 (MD5) / Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia) / IPEN/D-MPLO / Instituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP; Faculdade de Odontologia, Universidade de Sao Paulo

Made available in DSpace on 2014-10-09T12:52:55Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:01Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia) / IPEN/D-MPLO / Intituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP; Faculdade de Odontologia, Universidade de Sao Paulo