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In this work, a recently developed carbon nanodots (CnDs) were introduced in the mesoscopic TiO2 to form a TiO2: CnDs composite, to be used as an electrode in CH3NH3PbI3 based perovskite devices. It resulted the improvement in morphology of perovskite film and induced a carbon-doping passivating the oxygen defects. In addition, the presence of carbon dots enhanced the charge carrier mobility of TiO2 and provided extra photo-generation ability to the perovskite device due to its absorbing nature. The improved morphology, carbon-doping, photogeneration ability and the improved charge transfer characteristics with the introduction of carbon dots was verified by the scanning electron microscopy (SEM), atomic force microscopy (AFM), X-Ray photoelectron spectroscopy (XPS), UV-visible absorption, X-ray diffraction, space charge limited current (SCLC) measurement, photoluminescence (PL), electrochemical impedance spectroscopy (EIS), current leakage and open circuit photovoltage decay (OCPD) measurements. An optimized concentration of CnDs (3 wt%) within the TiO2 resulted in a maximum power conversion efficiency of 19.45% with negligible hysteresis, which is 16% higher than the device with pristine TiO2.

A comparative study of hydrogen evolution in devices based on cadmium chalcogenides quantum dots (CdS, CdSe and CdTe) and its combinations, sensitizing TiO2 was carried out. A maximum photocurrent of 2.7 mA cm−2 at 0 V bias, and a solar-to-hydrogen (STH) conversion efficiency of 0.9%, was obtained with CdSe QDs due to its wide absorption range. The co-sensitized device with CdS–CdSe QDs showed a higher photocurrent of 3.9 mA cm−2 with an STH of 1.2%. The improvement in hydrogen generation for electrodes sensitized with CdS in combination with CdSe or CdTe QDs, was attributed to the increased light absorption and appropriate band alignment for the enhanced charge transport.

Organic-inorganic inverted perovskite solar cells have been analyzed. This structure uses organic semiconductors as electron and hole selective electrodes and the perovskite as light harvesting layer. The anti-solvent deposition method is a frequently used techniques in the elaboration of conventional perovskite solar cells (FTO/TiO2/CH3NH3PbI3/Spiro-OMetad/Au). However, the anti-solvent method is seldom used in the inverted structure. In this work, we use the anti-solvent method to fabricate the perovskite film for solar cells in the ITO/PEDOT:PSS/CH3NH3PbI3/PC61BM/Ag configuration, systematically studying the effect of the anti-solvent dripping time and the relative humidity in cell fabrication and performance. The morphological, optical and photovoltaic analyses indicate that the right combination of these two parameters will result in a preferential crystal growth in the (1 1 0) orientation. This allows the formation of homogeneous pinhole-free films that enhance light harvesting and reduce charge-carrier leakage, hence increasing short circuit current and fill factor to obtain a photo-conversion efficiency of about ∼10%.

We for the first time report the incorporation of cobalt into a mesoporous TiO2 electrode for application in perovskite solar cells (PSCs). The Co-doped PSC exhibits excellent optoelectronic properties; we explain the improvements by passivation of electronic trap or sub-band-gap states arising due to the oxygen vacancies in pristine TiO2, enabling faster electron transport and collection. A simple postannealing treatment is used to prepare the cobalt-doped mesoporous electrode; UV-visible spectroscopy, X-ray photoemission spectroscopy, space charge-limited current, photoluminescence, and electrochemical impedance measurements confirm the incorporation of cobalt, enhanced conductivity, and the passivation effect induced in the TiO2. An optimized doping concentration of 0.3 mol % results in the maximum power conversion efficiency of 18.16%, 21.7% higher than that of a similar cell with an undoped TiO2 electrode. Also, the device shows negligible hysteresis and higher stability, retaining 80.54% of the initial efficiency after 200 h.

The formation of smooth, dense, and uniform perovskite layers on substrates is crucial for achieving high-performance perovskite devices. Here, we show that the introduction of a small concentration of cesium iodide to the precursor solution has a considerable effect on the morphology, phase and optoelectronic properties of CH3NH3PbI3-based perovskite films. An optimized concentration of 3% produces a high-quality perovskite film with a large grain size of ∼1.8 μm and a root mean square roughness of 5.917 nm. The improved morphology and high optoelectronic quality of the perovskite layer were verified by SEM, AFM, XRD, and UV-visible, photoluminescence and electrochemical impedance spectroscopy. The defect-free thin perovskite layer enables the fabrication of a mesoscopic CH3NH3PbI3-based perovskite device under ambient conditions, with a maximum power conversion efficiency of ∼19% with negligible hysteresis and high reproducibility. This method can be extended to other complexes of perovskite used in the present state-of-the-art perovskite solar cells.

In this work, the transparent TiO2 photoelectrodes have been synthesized by the sol?gel method and the dip-coating technique, incorporating three rheological agents as porous template ? Triton X-100, polivinilpirrolidone (M.W. 10000) and Pluronic F-127 into the TiO2 sol for the application in dye- -sensitized solar cells. Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, m-lines and UV?Vis spectroscopy analyses were carried out to examine the chemical composition, structure, morphology, thickness and optical transmittance of the TiO2 photoelectrodes. Impedance spectroscopy was carried out to analyze the cells? behaviour. An average energy conversion efficiency of 1.04 % was achieved using triton as a modifier of the transparent TiO2 film, obtaining a thickness about 1.21 ?m, a crystallite size of about 7 nm in the anatase phase and the porosity of about 53.4 %. Triton proved to be efficient for obtaining transparent and porous semiconductor films, while increasing the photoelectrochemical device?s performance.

Recently, CdSeTe Quantum Dot Sensitized Solar Cells (QDSSC) have shown remarkable advances in the photo conversion efficiency. In this work, the synthesis of CdSeTe QD is demonstrated and its performance as a sensitizer evaluated in a TiO 2 solar cell device. A photoconversion efficiency of 6.4% was obtained with the configuration TiO 2 /CdS/CdSeTe/ZnS that represent a fivefold increment compared to TiO 2 /CdSeTe/ZnS. The corresponding photocurrent was 20.3 mA/cm 2 as a result of the increase in the absorption range with the introduction of CdSeTe QDs and the electron injection of CdS. Electrochemical impedance spectroscopy (EIS) analysis confirms that such improvement was obtained as a result of the surface passivation of TiO 2 with the deposition of CdS acting also as a sensitizer if the appropriate energy level alignment between CdS and CdSeTe QDs is observed.

Highly smooth organo-lead halide perovskite (OHP) films with less intra-granular defects are necessary to minimize the non-radiative carrier recombination in photovoltaic devices. Herein, a simple air-extraction anti-solvent deposition (AAD) technique is proposed to improve the quality of perovskite films. An air extraction process accompanied by anti-solvent washing helps to improve the morphology of perovskite, leading to smooth, homogeneous, compact, pin-hole free and densely packed films. Perovskite films with an average roughness of 5.01 nm, which is the smoothest morphology in mesoscopic-perovskite solar cell to the extent of our knowledge, high crystallinity, and a crystallite size in the range of ∼500 nm to 1 μm have been achieved. Average power conversion efficiency (PCE) of 16.99% for 15 cells and a best PCE of 17.70% with a high open circuit voltage of 1.075 and fill factor of 74.22% were achieved using the AAD approach without a glove box. The cells exhibit virtually no hysteresis. These efficiency values are approximately 37.68% higher than the cells fabricated using anti-solvent process without air-extraction, where an average efficiency of 12.34% was measured. This method demonstrates high reproducibility and can be employed for the large scale production of PSC at reduced cost.

In this work, we demonstrate an enhancement of photocurrent in QDSSCs based on CdS (QDs)/CdSe Quantum rods (QRs)/CdSeTe (QDs) heterostructure due to the increased photon harvesting in the VIS-NIR region. The photo-conversion efficiency increased from 2.7% up to 6.5% when CdSe QRs and CdSeTe QDs were added in the reference cell: TiO2/CdS/ZnS and the devices reached a maximum photocurrent of 21.5 mA cm−2. This outstanding performance was caused by a broadening of the light absorption in the VIS and NIR regions, this in turn, was produced by the presence of CdSe QRs and CdSeTe QDs in the cells. The use of additional SiO2 layer in the solar cell that contained CdSe QRs and CdSeTe QDs allowed us to improve the efficiency of the cells even more (up to 7.4%), since it decreased the recombination rate produced by defects and interfaces in the QDs. Moreover, the effect on the solar cells performance was studied as the size of the CdSeTe QDs introduced into them increases and found that both, the values of photocurrent and efficiency are enhanced as the size of the CdSeTe increases. We associated this improvement of performance to the increase of light absorption in the NIR region as the size of the CdSeTe QDs increases. Hence, our results suggest that the strategy of adding CdSeTe QDs with different sizes together with CdSe QRs is promising to enhance the efficiency of QDSSCs.

Within the body of research aimed at improving the photovoltaic performance of quantum dot-sensitized solar cells (QDSSC), poly-3-alkyl thiophenes have been commonly used in hybrid photovoltaic devices. The roles of poly(3-hexylthiophene) (P3HT) and of poly(3-octylthiophene) (P3OT) on hybrid QDSSC were investigated in the present work. To this end, CdS and ZnS QDs were deposited by successive ionic layer adsorption and reaction method on TiO2 mesoporous film. The polymers were added by drop-casting method giving the configurations TiO2/CdS/ZnS/P3HT and TiO2/CdS/ZnS/P3OT. Results showed that the polymer covers the TiO2/CdS/ZnS surface enough to protect it from contact with the polysulfide electrolyte, while electrochemical impedance spectroscopy measurements indicated that when P3HT and P3OT were employed, the recombination resistance increased and the transport resistance decreased, causing the improvement of the open circuit voltage and fill factor, respectively.

Tridoped ZrO 2 :Yb 3 + –Er 3 + –Bi 3+ nanophosphor was synthesized by hydrothermal process and demonstrated the possibility of switching from a strong green–yellow broadband signal to red emission due to Bi 3+ and Er 3+ ion by changing excitation from 350 nm to 970 nm, respectively. The green–yellow band is associated to the transition 3 P 1 → 1 S 0 and was overlapped with the green band associated to the transition 2 H 11/2 + 4 S 3/2 → 4 I 15/2 of Er 3+ as a result of the energy transfer from Bi 3+ to Er 3+ . The strong red band is associated to 4 F 9/2 → 4 I 15/2 transition of Er 3+ and enhanced by a factor of 3 as a result of the forward and backward energy transfer process (Er 3+ → Bi 3+ → Er 3+ ). This sink effect where electrons can be stored temporally and released back can be useful to enhance the emitted signal of other lanthanides.

Bismuth sulfide (Bi 2 S 3 ) is an attractive potential replacement for lead sulfide (PbS) due to its low toxicity and near infrared absorption spectrum. In this work, we report the photovoltaic characteristics of cadmium sulfide (CdS) and Bi 2 S 3 quantum dots (QDs) sensitized solar cells. The QDs were grown by the successive ionic layer adsorption and reaction (SILAR) method. The number of cycles was varied in order to optimize the photoconversion efficiency. Using a photovoltaic device with the structure TiO 2 /CdS/ZnS as our reference, we obtained increments in the short circuit current (J sc ) from 7.9 to 9.3 mA/cm 2 , the fill factor (FF) from 41.9 to 53.7%, and the photoconversion efficiency (η) from 1.7% to 2.52% for the configuration TiO 2 /CdS/Bi 2 S 3 /ZnS. This enhancement is explained by an augmented absorption spectral range and a favorable energy level diagram. Electrochemical impedance measurements were performed to better understand the carrier recombination and transport processes.

We investigate the effect of the incorporation of a material with efficient electron transport into a Hybrid Quantum Dot Sensitized Solar Cell (HyQDSSC). The performance of different quantum dot sensitized solar cells is compared with a cell containing poly [(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) with structure TiO2/PbS/PFN/CdS/ZnS. The photoconversion efficiency, as compared to our reference samples, was enhanced in some cases by approximately 45%, while the short-circuit current increased by up to 100% after the incorporation of PFN. The deposition order of the different components was crucial in achieving these improvements. Diffuse reflectance and impedance spectroscopy were used to study the behaviour of the cells. The observed enhancements are attributed to increased light scattering in the active layer, better charge transport, and a decrease in charge recombination and transport resistance.

A multilayered semiconductor sensitizer structure composed of three differently sized CdSe quantum rods (QRs), labeled as Q530, Q575, Q590, were prepared and deposited on the surface of mesoporous TiO2 nanoparticles by electrophoretic deposition (EPD) for photovoltaic applications. By varying the arrangement of layers as well as the time of EPD, the photoconversion efficiency was improved from 2.0% with the single layer of CdSe QRs (TiO2/Q590/ZnS) to 2.9% for multilayers (TiO2/Q590Q575/ZnS). The optimal EPD time was shorter for the multilayered structures. The effect of CdS quantum dots (QDs) deposited by successive ionic layer adsorption and reaction (SILAR) was also investigated. The addition of CdS QDs resulted in the enhancement of efficiency to 4.1% for the configuration (TiO2/CdS/Q590Q575/ZnS), due to increased photocurrent and photovoltage. Based on detailed structural, optical, and photoelectrical studies, the increased photocurrent is attributed to broadened light absorption while the increased voltage is due to a shift in the relevant energy levels.

The performance of perovskite solar cell (PSC) is highly sensitive to deposition conditions, the substrate, humidity, and the efficiency of solvent extraction. However, the physical mechanism involved in the observed changes of efficiency with different deposition conditions has not been elucidated yet. In this work, PSCs were fabricated by the antisolvent deposition (AD) and recently proposed air-extraction antisolvent (AAD) process. Impedance analysis and J–V curve fitting were used to analyze the photogeneration, charge transportation, recombination, and leakage properties of PSCs. It can be elucidated that the improvement in morphology of perovskite film promoted by AAD method leads to increase in light absorption, reduction in recombination sites, and interstitial defects, thus enhancing the short-circuit current density, open-circuit voltage, and fill factor. This study will open up doors for further improvement of device and help in understanding its physical mechanism and its relation to the deposition methods.

Semi-transparent polymer light emitting diodes (PLEDs) with double side emission using multiwall carbon nanotubes (MWCNT) sheets as top transparent cathode are described. The combination of an effective electron injection layer (EIL) and a hole blocking layer (HBL): PFN/Cs2CO3, allowed an enhancement of the electron injection from the MWCNT sheets. Those semitransparent devices exhibited a brightness and an efficiency of 220 Cd/m2 and 0.54 Cd/A, respectively, which were measured on the glass side. Our results indicate that the new architecture of laminated top-MWCNT could be useful for the development of transparent displays using a vacuum free simple dry fabrication process.

Solution-processed mesoscopic oxide semiconductor-based materials offer potentially low-cost and high stability alternative for next generation of water to hydrogen conversion photoelectrochemical cells (PEC). In the present study, we demonstrate the effective unassisted H2 generation by a tandem device based on a quantum dot (QD)-dye dual absorber system. These systems are constituted by a TiO2 mesoscopic photoanode sensitized with CdS QDs and a dye sensitized solar cell (DSSC), based on ruthenium dye, connected in series. This solar cell supplies the needed photovoltage to induce photodriven hydrogen production. Opto-electrochemical characterization of the single components allows the prediction of the operational photocurrents and a reliable estimation of the theoretical power conversion efficiencies of tandem systems. Evolved hydrogen under simulated solar illumination was collected, and solar to hydrogen conversion efficiencies (STH) were obtained. The tandem devices have demonstrated high stability in aqueous medium and solar-to-hydrogen conversion efficiency of (0.78 ± 0.04)%, near tripling the efficiency of single QD based photoanodes. These results highlight the importance of the design of hybrid photoanodes combining the effect of different light absorbers working in parallel tandem devices for the development of efficient H2 generation QD-based photoelectrochemical cells. © 2013 American Chemical Society.

It is reported the white light emission from a hybrid polymer light emitting diode (HyPLED) which has a film of YAG:Ce3+ nanoparticles. This white light is produced due to the combination of the blue light generated from a PLED and the green-yellow light coming from YAG:Ce3+ nanoparticles. This white light has CIE (International Commission on Illumination) coordinates of (0.31, 0.35) which is near of the ideal coordinate of (0.33, 0.33). The hybrid device presents a turn on voltage of 4 V, as well as a maximum luminance and efficiency of 266 cd m−2 and 0.34 cd A−1 (at 9 V), respectively. Finally, it was possible to tune the color emission from green to bluish-white by changing the operation voltage.

In this work are presented the results obtained with solar cells sensitized with quantum dots of cadmium sulphide (CdS) incorporating luminescent materials (NaYF4:Yb/Er). The study revealed that through using a bifunctional layer of NaYF4:Yb/Er submicron rods, the infrared radiation is absorbed in 980nm to generate luminescence in the visible region to 530nm, under the UP-conversion process, in the same way simultaneously, NaYF4:Yb/Er layer causes scattering toward the quantum dots, the emission and scattering generated by this material is reabsorbed by the QD-CdS, and these in turn are absorbing in its range of solar radiation absorption, Thus generates an increase in the electron injection into the semiconductor of TiO2. The results of a cell incorporating NaYF4: Yb/Er at 0.07M shown photoconversion efficiencies of 3.39% improving efficiency with respect to the reference solar cell without using NaYF4: Yb/Er of 1.99%. The obtained values of current and voltage showed a strong dependence of the percentage of NaYF4 Yb/Er, and the mechanism of incorporation of this material.

Light-emitting diode (LED) sources have evolved to encompass a wide range of non-conventional and novel approaches in many illumination applications. This paper surveys some optical aspects of nonconventional LED based illumination.

Strong green-yellow emission in Eu2+ doped glass ceramic as a function of rare earth concentration was obtained. Proof of concept for solid state white lighting with high power AC LED was fabricated.

Strong visible green upconversion emission in nanocrys- talline BaZrO3:Yb 3+ powder, obtained by a hydrothermal process at 100 - C, is reported. The unconverted emission has a quadratic depen- dence on the pump intensity with a lifetime around half that of the NIR lifetime. Results suggest cooperative upconversion as the mechanism responsible for the green ∞uorescence. This e-cient Yb 3+ -based coop- erative up-conversion process allows the development of novel emitting materials in the ultraviolet to visible (UV-VIS) range.

The procedure employed for the sensitization of mesoporous photoanodes affects strongly the final performance of sensitized devices, especially when semiconductor quantum dots and quantum rods are used as sensitizers. In this work the effect of three different sensitizing methods in the final cell performance was analyzed. The TiO2 films were sensitized with CdS QDs grown by successive ionic layer adsorption and reaction, SILAR, and with CdSe quantum rods deposited by electrophoretic and pipetting methods. Several configurations of the sensitizers and combinations of sensitization methods were tested. 4% photoconversion efficiencies were obtained for TiO2 electrodes sensitized with CdS and CdSe by electrophoretic and pipetting respectively, while for the sensitizer with both techniques the efficiency was 4.7%. This high efficiency is mainly due to the high fill factor (60%) and the photocurrents (13.1 mA/cm2) obtained by the correct combination of near-infrared and visible light photoabsorption, the better CdSe QRs distribution in the TiO2 film and a passivation of the TiO2 nanocrystals. Electrochemical impedance measurements has been analyzed and discussed in detail providing a detailed analysis of recombination resistance and charge transport processes. These parameters have been correlated with the cell performance. We acknowledge fi nancial support from CONACYT through Grant 134111, the UC-MEXUS program Grant 00007, CIO- UGTO 2013-2015, and the CEMIE-Solar (04002) consortium. D.E. and A.C.-P. acknowledge scholarships from CONACYT, I.Z. acknowledges CONACYT for the postdoctoral fellow, and thanks are given to Maria Christian Albor for SEM and EDS analysis.

Color-temperature tunable white organic light emitting diodes (WOLEDs) in parallel tandem configuration were fabricated by using TFB:MEH-PPV (yellow emitter) in the bottom subunit and TBADN (blue emitter) in the top subunit. In this parallel tandem architecture, a thin film of silver was an active common anode, which permitted to inject holes into top and bottom subunits simultaneously. This common injection electrode also allowed to tune the color temperature (CCT) and CIE coordinates of white light emission from cool (CIE: 0.33, 0.25; CCT = 5218 K) to warm (CIE: 0.38, 0.39; CCT = 3926 K) by controlling the brightness of the yellow light and blue light emitted in the bottom and top subunits respectively. The performance of the parallel tandem was compared with that of in-series tandems and additional advantages of the parallel architecture such as tunable chromaticity, lower turn on voltage (4 V compared to 7 V in the in-series tandem) and higher brightness (∼15%) were found. The closest CIE coordinate obtained for white light was (0.35, 0.35), which is near to the ideal coordinate of (0.33, 0.33) for pure white light. Thus, the results indicate that these white OLEDs in parallel configuration can be potentially useful for displays and lighting applications.

We report yellow electroluminescence of a QD-LED using a hybrid structure. Alq3 was used as electron injection layer and CdSe QDs as emitters. The device has Commission Internacionale de l’Enclairage (CIE) coordinates of (0.429, 0.493).

A temperature sensor based on the unbalanced Hi-Bi fiber Sagnac interferometer is analyzed in the temperature interval 15 250 C. It is shown that the sensitivity of such a sensor exhibits irreversible changes at temperatures higher than 200 C. To achieve this, it is proposed to anneal the fiber at 200 C for 1.5 h to avoid hysteresis and extend the measured temperature interval. Measurements were done for the polymer-coating-induced birefringence and the residual stresses causing hysteresis. It is also shown that the sensor sensitivity is reduced by 27 % when stresses are removed.

A Mueller-Stokes analysis is applied to pure bismuth thin film samples prepared by the laser ablation technique by using a polarimeter with a 632.8 nm continuum wavelength laser. The complex refractive index is determined in the range of 250-1100 nm. Results from the Mueller matrix show the high sensitivity of diattenuation and polarizance parameters as a function of the sample thickness and the incidence angle, except at the pseudo-Brewster angle, where they exhibit the same value. Results show that the knowledge of the polarimetric response, with appropriate incident polarization states, could be used to design photonic Bi-based devices for several applications. Polarization dependence is the result of changes on the surface morphology as a result of the small value of the skin depth.

This work presents the structural, morphological and luminescent properties of Y 3 Al 5 O 12 :Ce 3+ (0.1%)-Pr 3+ (0.1%) nanophosphors synthesized by a hydrothermal precipitation method. It was observed that the incorporation of Amonium hydroxide (NH 4 OH, Ammonia) increases the YAG (%)/YAM(%) ratio, leading to an increase of 83% in the overall emission under 460 nm excitation. The nanophosphor with the highest content of YAM, presented the best broad green-yellow- red emission band corresponding to Ce 3+ and Pr 3+ emissions under 340 nm excitation. The average nanocrystallite size was 50 and 55 nm for the samples with and without Ammonia respectively. Quenching of the overall emission after an annealing treatment at 1100°C is observed in spite of reaching single YAG crystalline phase. That suggests Pr 4+ and/or color centers formation due to the estequiometric unbalance as a consequence of the YAM to YAG transformation. By taking advantage of the broad emission under 340 nm and using a blue dye, we produced white light with CIE coordinates of (0.30, 0.36).

O ambiente competitivo atual leva as empresas a optarem por uma competência central e por se associarem, em parceria, a outras empresas para aproveitar uma oportunidade de mercado. Essa associação torna-se cada vez mais dinâmica à medida que o ciclo do produto se encurta. Este artigo propõe a expansão dos métodos de Tecnologia de Grupo às aplicações que tratam do projeto de parceria entre empresas. Considera, numa primeira fase, a similaridade entre as atividades necessárias à execução de um produto e gera um dendrograma que auxilia o gestor definir a configuração da montagem do produto, e, numa segunda fase, sugere a utilização da distância Euclidiana entre a empresa candidata e a empresa ideal como elemento de escolha de parceira, tendo como critério quanto uma empresa é semelhante à outra nas ações que desenvolve para a competitividade. Uma aplicação mostra a utilidade da metodologia sugerida. Os resultados mostram ser promissora a utilização da grande experiência hoje existente na definição de células de manufatura para a escolha das empresas que venham a compor uma parceira em um sistema de produção multiempresas. Palavras-chave: Parceria entre empresas. Sistemas de manufatura. Consórcio modular. Teoria de similaridade. Estratégia competitiva.

Parallel tandem organic light emitting devices (OLEDs) were fabricated with transparent multiwall carbon nanotube sheets (MWCNT) and thin metal films (Al,Ag) as interlayers. In parallel monolithic tandem architecture, the MWCNT (or metallic films) interlayers are an active electrode which injects similar charges into subunits. In the case of parallel tandems with common anode (C.A.) of this study, holes are injected into top and bottom subunits from the common interlayer electrode; whereas in the configuration of common cathode (C.C.), electrons are injected into the top and bottom subunits. Both subunits of the tandem can thus be monolithically connected functionally in an active structure in which each subunit can be electrically addressed separately. Our tandem OLEDs have a polymer as emitter in the bottom subunit and a small molecule emitter in the top subunit. We also compared the performance of the parallel tandem with that of in series and the additional advantages of the parallel architecture over the in-series were: tunable chromaticity, lower voltage operation, and higher brightness. Finally, we demonstrate that processing of the MWCNT sheets as a common anode in parallel tandems is an easy and low cost process, since their integration as electrodes in OLEDs is achieved by simple dry lamination process.

This work reports the luminescence, morphology and synthesis of ZnO quantum dots using a simple wet chemical method and different concentrations of Triethanolamine (TEA) as surfactant. Those nanoparticles emitted a strong blue emission band centered at 429 nm when they are dispersed in hexane. Spherical quantum dots with sizes ranging from 3 to 7 nm were obtained for concentrations from 0 to 0.7 ml. of TEA, whereas a mixture with oval-like nanoparticles was observed from concentrations above of 1.1 ml of TEA. It was also possible to control the values of the band gap in ZnO quantum dots depending on the content of TEA. Based on the high quantum yield of 81% measured for those ZnO nanoparticles respect to quinine sulfate dye (QS), it is suggested that such nanoparticles could be used for biolabeling and ZnO based LEDs.

Chemical oxidation doping effect produced by 3000 ppm of NO2 with N2 balance on spin coated regioregular head-to-tail poly(3-octylthiophene) (P3OT) thin films is reported. Undoped and doped states mechanisms are discussed based on changes in optical absorptiometry, surface analysis and refractive index. The two midgaps created for few minutes in the P3OT under NO2 doping effect by the polarons and bipolarons for mobility capabilities and its final doped state has been optically monitored and discussed. A significant change on the surface of undoped and doped P3OT thin films was inspected by atomic force microscopy (AFM). A P3OT refractive index transition from 1.69 (undoped) to 1.55 (doped) has been observed and discussed. Finally, the electrostatic attraction between the polaron and its counter ion (NO2-) has been analyzed for the possibility to diffuse the counter ion from the P3OT thin films and make possible its backward state (reversibility). The theoretical and experimental data results presented are part of a fiber optic chemical sensor (FOCS) project for NO2 particles detection.

The photoluminescence and crystalline structure characterization of undoped and several samarium and erbium doped ZrO 2 samples are reported. Strong visible fluorescence emission produced by the transitions 4 G 5/2 → 6 H 5/2,7/2,9/2 of Sm 3+ was obtained by the excitation of the host at 320 nm (downconversion). Green (545 nm) and red (680 nm) emissions bands were observed under 962 nm excitation (upconversion). Experimental results showed that the emission bands could be tuned by controlling the Er 3+ concentration. In particular, for the highest Er 3+ concentration, the red band is enhanced under 962 nm excitation. The nature of this behavior is discussed taking into account the concentration dependent non-radiative energy transfer ( 4 I 13/2 + 4 I 11/2 ) → ( 4 F 9/2 + 4 I 15/2 ) and cross-relaxation ( 2 H 11/2 + 4 I 15/2 ) → ( 4 I 9/2 + 4 I 13/2 ) process.

The photoluminescence (PL) and thermoluminescence (TL) characterization of undoped and cerium and terbium doped nanocrystalline Y3Al5O12 (YAG) prepared by the sol-gel method is reported. The experimental results of the PL show the typical emission bands centered at 490, 543 and 590 nm for YAG:Tb3+ and 530 nm for YAG:Ce3+ when excited with 325 and 345 nm light, respectively. The TL signal was obtained after exposure to UV-, X- and β- irradiation. The thermoluminescence results indicate that YAG:Tb3+ sample is very sensitive to all type of irradiation used, being highly sensitive for UV-irradiation. The high efficiency of the TL and PL suggests a good potential of this material as radiation dosimeter as well as active optical windows and new generation television screen.

Polystyrene dye doped plastic optical fiber was prepared and used to detect gamma and beta radiation from I151 and TeO4 gamma tracers typically used to get images of tumor areas within the human body. Absorption and fluorescence emission of TMQ, PBDBD365, POPOP styrene doped was performed under gamma and UV-irradiation. The fluorescence efficiency of the binary system PBDBD365-POPOP and the ternary TMQ- PBDBD365-POPOP was compared and according to the experimental results it was shown that the presence of the TMQ dye enhance the fluoresce obtained under I151 radiation. Systematic characterization of the binary system was performed as function of primary dye concentration .

We present side induced fluorescence (SIF) results on laser dye doped unclad plastic optical fibers. The SIF data can be used to obtain optical loss spectra for the low loss region of the absorption tail of the laser dye that has been doped into the fiber. Dyes which have been examined include derivatives of rhodamine and pyromethene. SIF deduced loss results in combination with cutback loss measurements on undoped fibers suggest that the electronic absorption of the laser dye dominates the loss far (> 200 nm) from the peak of the dye absorption (the order of 0.5 cm-1 at 750 nm). Loss measurements of unclad undoped fibers suggest that loss is dominated by scattering and defect mechanisms. In fact these losses are quite high compared to literature measurements of analogous clad fibers. Thus intrinsic loss of the polymer (PMMA in most cases) is minor compared to scattering and defect losses when dealing with unclad fibers. We also present the fit of our dye-doped fiber loss data to homogeneous and inhomogeneous broadening equations and show that broadening is dominated by inhomogeneous mechanisms as is expected.

Tunable white light emission was obtained from ZnO nanorods with lengths ranging from 125 to 165 nm and quantum dots with an average size of 5 nm, synthesized with dodecylamine (DCA) as surfactant. It was possible to tailor the emission from cool to warm white light by changing the concentration of DCA in the synthesis process. The CIE coordinates for the white light obtained were (0.33, 0.32) in the case of photoluminescence and (0.31, 0.33) for electroluminescence from ZnO-based LEDs with a turn-on voltage of 4 and 6 V and a maximum current consumption of 2.32 mA at 10 V.

Acrylic plastic optical fibers containing the laser dye Rhodamine B chloride have been drawn from unclad doped acrylic preforms. The fibers strongly emit waveguided fluorescence light produced form ambient side illumination along the length of the fiber. We have characterized the loss in the wavelength region of strong absorption by measuring the attenuation of the side induced fluorescence (SIF) produced by He-Ne (green) and He-Cd (blue) laser lines. We can accurately quantify the loss in the high loss spectral region using SIF. Attenuation data and the associated SIF analysis will be discussed.

We discuss plastic optical fiber technology in the context of its relationship to glass optical fiber technology. POF technology serves as a low cost way to investigate innovative optical fiber material structures. POFs offer some application advantages, especially in low cost broad bandwidth easily interconnected local area networks. Applications to space technology include scintillation sensing and other specialty sensing fibers.

A solution based hydrothermal method is used for the preparation of LaPO4:Yb–Tm doped and LaPO4:Yb/Tm core-shell upconverted nanorods. The morphologies, structure, formation mechanism, and upconversion emission properties of these nanocrystals are investigated in detail. Tensile strain is observed for LaPO4:Yb–Tm doped material but compressive strain is obtained for LaPO4:Yb/Tm core-shell material. Analysis suggests that the lattice strain plays an important role on the upconversion emission. Bright blue (475 nm) and red (650 nm) upconversion emissions associated to G14→H36 and F32→H36 transitions were observed and a significant higher in upconversion emission intensity is observed in core-shell nanorods. The effective decay time calculated are 230 and 110 μs for core-shell and doped nanorods, respectively, indicating the removal of surface defects due to surface coating. It reveals that the core-shell structure shows better upconversion emission efficiency.

Advances in plasmonic nanoparticle synthesis afford new opportunities for biosensing applications. Here, we apply a combination of a new type of plasmonic nanomaterial – stellated nanoparticles, and polarization-sensitive darkfield microscopy for detecting molecular assemblies and tracking of individual epidermal growth factor receptors within single live cells with high signal-to-background ratio. Depolarization of linear polarized light by stellated nanoparticles is over 15-fold more efficient than similarly-sized spheroidal nanoparticles. This efficient light depolarization allows robust detection of molecules labeled with stellated nanoparticles in cross-polarized imaging where the intrinsic light scattering from cells is significantly reduced. The imaging can be carried out with single molecule sensitivity for essentially unlimited time with no signal degradation.

Energy conversion of 3% was achieved in Gratzel-type solar cells. These solar cells were made in a tick TiO2 transparent layer (9 µm) sensitized with CdS using the chemical bath method.