The PV performance and aging/stability of organic photovoltaic (OPV) devices based on the well-known system PTB7:[70]PCBM and an alternative air-stable electrode deposited at room conditions are fully studied when the active area is scaled by a factor of 25. On the other hand, the aging/stability processes were also studied through single diode model, impedance spectroscopy and light-beam induced current (LBIC) measurements in accordance with the established ISOS-D1 (dark storage) and ISOS-L1 (illumination conditions) protocols. Results are a good indication that the alternative cathode Field’s metal (FM) cathode works as an encapsulating material and provides excellent PV performance comparable with the common and costly high-vacuum evaporated Al cathode.
Efficient solid state lighting devices based in inorganic emissive materials are now available in the market meanwhile for organic emissive materials still a lot of research work is in its way. [1,2] In this work a new organic emissive material based on carbazole, N-(4-Ethynylphenyl) carba-zole-d4 (6-d4), is used as electron-acceptor and commercial PEDOT:PSS as the electron-donor to obtain white emission. Besides the HOMO-LUMO levels of materials the white emission showed dependence on the films thicknesses and applied voltages. In here it is reported that by diminishing the thickness of the PEDOT:PSS layer, from 60 to 35 nm, and by keeping the derivative carbazole layer constant at 100 nm the electro-luminescence (EL) changed from emissive exciton states to the mixture of emissive exciton and exciplex states. [3] For the former thicknesses no white light was obtained meanwhile for the later the EL spectra broadened due to the emission of exciplex states. Under this condition, the best-achieved CIE coordinate was (0.31,0.33) with a driving voltage of 8 V. To lower the driving voltage of the devices a thin film of LiF was added between the derivative of carbazol and cathode but the CIE coordinates changed. The best CIE coordinates for this case were (0.29, 0.34) and (0.32, 0.37) with driving voltage of about 6.5 V.
Acknowledgments: CeMie-Sol/27 (Mexico) 207450
References
[1] Timothy L Dawson, Society of Dyers and Colourists, Color. Technol., 126, 1–10 (2010),
doi: 10.1111/j.1478-4408.2010.00220.x
[2] G. M. Farinola, R. Ragni, Journal of Solid State Lighting, 2:9 (2015),
doi: 10.1186/s40539-015-0028-7.
[3] E. Angioni, et al, J. Mater. Chem. C, 2016, 4, 3851,
doi: 10.1039/c6tc00750c.
Organic molecular sensors have the advantage of being used through an easy, fast, economical and reliable optical method for detecting toxic metal ions in our environment. In this work, we present a simple but highly specific organic ligand compound 5-Chloro-2-((E)-((E)-3-(4-(dimethylamino)phenyl)allylidene)amino)phenol (L1) that acts as a colorimetric sensor for ions in a mixture of acetonitrile/water (ratio 10:1, v:v). Binding interaction between L1 and various metal-ions has been established by ultraviolet-visible spectroscopic measurements that indicate favorable coordination of the ligand with selective metal ions, particularly, with copper. These results showed that the electronic transition band shape of L1 change after binding with copper in aqueous solution. L1 exhibited binding-induced color changes from yellow to pink one detected by the naked eye. This new sensor presented 2.5 × 10-6 M as limit detection, even under the presence of other metal ions.
The search of clean and renewable energy sources is one of the most important challenges that mankind confronts.
Recently there has been a notable interest to develop organic photovoltaic (OPV) technology as a mean of renewable
energy source since it combines low-cost and easy fabrication. Most of the efforts have been directed to increase the
efficiency, leaving aside the durability of the organic materials, however, a new architecture known as inverted solar cell
might bring a never seen durability (years) that could make possible large scale applications of this technology. Here are
presented the results we achieved using both, the conventional and inverted architectures employing as organic donor
(D) the very well known semi-conducting polymer P3HT, in mixtures with the acceptor (A) fullerene PC61BM. The
morphology of thin polymer films prepared by using the spin coating technique was analyzed by AFM. For the
conventional architecture the cells were fabricated following the structure ITO/PEDOT:PSS/P3HT:PC61BM/Wood´s
metal, where the Wood´s metal cathode is an alloy that melts at 75 °C. For the inverted architecture the structure
ITO/ZnO/P3HT:PC61BM /PEDOT:PSS/(Ag, Cu or Silver paint) was used, where ITO worked as cathode by switching
its work function through the introduction of ZnO nanoparticles. Under tests using Xenon lamp irradiation at 100
mW/cm2, the conventional and the inverted architectures produced efficiencies of 1.75 % and 0.5 %, respectively. For
both architectures the chosen back-contact materials (Wood´s metal and silver paint) allowed us to easily make the OPVs
cells without the need of vacuum steps.
In this work we report new highly efficient organic photorefractive polymers based on aryl-cyano non-linear
chromophores [(4-(diethylamino)-2-hydroxybenzylideneamino]benzonitrile (CN-C-OH) and [4-(diethylamino)
benzylideneamino]benzonitrile (CN-S-OH). The PR polymer blends are composed by the photoconductor poly
(9-vinylcarbazole) and plasticizer 9-ethylcarbazole PVK:ECZ matrix, as well as the sensitizer fullerene C60.
Holographic experiments in a tilted four wave mixing (FWM) and two beam coupling (TBC) geometry were
carried out by using a 10 mW He-Ne laser (633 nm). The experiments were performed at room temperature to
measure the electric field steady-state diffraction efficiency dependence of the PR composites. High diffraction
efficiency as high as 90 % was observed for polymers based on CN-C-OH at 25 wt. % doping level and an
external applied electric field around 56 V/μm. The μβ product was also measured by EFISH technique for
compounds CN-C-OH and CN-S-OH, results showed that CN-C-OH present a value 3.5 times higher than CN-S-
OH, which is supported by a theoretical prediction. Demonstration of fast reversible holographic imaging (~0.5
s) by using these highly efficient organic photorefractive polymers based on CN-C-OH and CN-S-OH is
presented.
Colorimetric chemosensors are simple, economical and practical optical approach for detecting toxic metal ions (Hg2+,
Pb2+, Ni2+, etc.) in the environment. In this work, we present a simple but highly specific organic compound 4-chloro-2-((E)-((E)-3-(4-(dimethylamino)phenyl)allylidene)amino)phenol (L1) that acts as a colorimetric sensor for divalent metal
ions in H2O. The mechanism of the interaction between L1 and various metal-ions has been established by UV-vis
absorption and emission spectroscopic experiments that indicate favorable coordination of metal ions with L1 in
different solvents. Experimental results indicate that the shape of the electronic transition band of L1 (receptor
compound) changed after the interaction with divalent metal-ions, such as Hg2+, Pb2+, Mn2+, Co2+, Cu2+, and Ni2+ in
aqueous solution. We found that L1 have a considerable selectivity for Ni2+ ions, even in presence of other metals ions
when mixtures of DMSO/H2O as are used as solvents. L1, which has been targeted for sensing transition metal ions,
exhibits binding-induced color changes from yellow to pink observed even by the naked eye in presence of Ni2+ ions.
Nowadays the production of counterfeit and low quality drugs affects human health and generates losses to pharmaceutical industries and tax revenue losses to government. Currently there are several methods for pharmaceutical product analysis; nevertheless, most of them depend on complex and time consuming steps such as sample preparation. In contrast to conventional methods, Laser-induced breakdown spectroscopy (LIBS) is evaluated as a potential analytical technique for the rapid screening and quality control of anti-diabetic solid formulations. In this paper authors propose a simple method to analyze qualitatively and quantitatively Active Pharmaceutical Ingredients (APIs) such as Metformin hydrochloride. The authors used ten nanosecond duration pulses (FWHM) from a Nd:YAG laser produces the induced breakdown for the analysis. Light is collected and focused into a Cerny-Turner spectrograph and dispersed into an ICCD camera for its detection. We used atomic emissions from Chlorine atoms present only in APIs as analyte signal. The analysis was improved using Bromine as internal standard. Linear calibration curves from synthetic samples were prepared achieving linearity higher than 99%. Our results were compared with HPLC results and validation was performed by statistical methods. The validation analysis suggests that both methods have no significant differences i.e., the proposed method can be implemented for monitoring the pharmaceutical production process in-situ in real time or for inspection and recognition of authenticity.
In this work, fast and reliable spectroscopic methods in combination with chemometric tools were developed for
simultaneous determination of Acetylsalicylic Acid, Acetaminophen and Caffeine in commercial formulations. For the
first-order multivariate calibration method (PLS-1), calibration and validation sets were constructed with 23 and 10
samples respectively according to a central composite design. The Micro-Raman, FTIR-HATR and UV absorption
spectra in the region of 100-2000 cm-1, 400-4400 cm-1 and 200-350 nm, respectively, were recorded. The % REP's
(Percentage of relative error of prediction) was less than 18 for all used spectroscopic techniques. Subsequently,
commercial pharmaceutical samples were analyzed with percentage of recovery between 90 and 117% for the three
compounds.
The search of clean, inexpensive and renewable energy sources is one of the most important challenges that the mankind
is currently confronting. Recently there has been a notable interest of the scientific community to develop organic
photovoltaic (OPV) technology as a mean of renewable energy source since it combines low-cost and easy fabrication.
We have fabricated and tested plastic solar devices (OPVs) by using the bulk heterojunction approach. OPVs were
prepared by blending 6-Nitro-3-(E)-3-(4-dimethylaminophenyl)allylidene)-2,3 dihydrobenzo[d][1,3,2]-oxazaborole (M1)
and (E)-3-(4-Dimethylaminophenyl)allylidene)-2,3-dihydrobenzo[d]-[1,3,2]oxazaborole (M2), which are conjugated and
non-linear low molecular weight molecules prepared in our laboratories, and the well known photoconductor polymer
MEH-PPV; fullerene PC61BM was the sensitizer. The morphology of thin polymer films prepared by using the spin
coating technique was analyzed by Atomic Force Microscopy (AFM). For the electric contact, commercial and
transparent indium tin oxide (ITO) deposited on glass slides was used, and a metal alloy of Pb/Bi/Cd/Sn as cathode, was
easily deposited on the polymer film by melting the alloy at 75 °C. Open circuit voltages (Voc) of ~ 700 mV and short
circuit currents (Jsc) of ~ 0.75 mA/cm2 under solar (AM1.5) illumination were measured for MEH-PPV and M1 based
samples. For OPVs cells based on mixtures of either M1 and MEH-PPV or M2 and MEH-PPV there was a large
electrical enhancement showing Voc ~ 700 mV and Jsc ~ 2.0 mA/cm2. OPVs cells were also tested under Xe-lamp
illumination. Measurements from the I-V curves gave electrical efficiencies close to 1%.
An alternative method to chromatography is reported to discriminate among white and aging tequilas. In a previous
work we had reported a similar method to discriminate between 100% blue agave and mixed tequilas. A data base of
145 tequilas was created where well known tequila brands and tequilas in bulk were included. The bottled tequilas were
purchased at various Mexican liquor stores to ensure that different batches of each brand were included in the data base.
The method that we propose to discriminate tequilas may also be used for quality control in distilleries and, with the
help of the data base, to identify counterfeit tequilas.
Third-order nonlinear properties of polymer films doped with triarylmethane dyes have been measured by using third-harmonic generation (THG) for fundamental wavelengths within the range 1 100 nm - 1 600 nm. Our studies show that the triarylmethane dyes Crystal Violet and Ethyl Violet, with a multidirectional charge transfer in their 3-fold symmetry structure (octopolar dimensionality), exhibit large third-order nonlinear coefficient and low residual absorption for harmonic wavelengths, leading to a high conversion efficiencies of THG. The studied films are good candidates for ultra-fast optical correlators.
The preparation and characterization of organic photorefractive polymer composites derived from (2-(p-chlorophenyl)-(3'-nitrobenzo[d])-(4''-methoxybenzo[h])-1,3-dioxa-6-aza-2-boracyclonon-6-ene, a push-pull boronate, which shows NLO properties, are described. The polymers are based in the photoconductor poly(9-vinylcarbazole) and the plasticizer 9-ethylcarbazole PVK:ECZ matrix, and C60 as sensitizer. For the photorefractive performance, two different chromophore concentrations were used, in addition, the ratio of PVK:ECZ was varied to see the effect on the room temperature molecular orientation. Holographic experiments in a tilted four and two wave mixing geometry were performed by using a 10 mW He-Ne laser (632.8 nm). The experiments were performed at room temperature, with a fixed grating spacing Λ of 2.9 μm, for determining the electric field steady-state diffraction efficiency dependency and the optical gain of the composites. Acceptable photorefractive properties were observed for a polymer with a glass transition temperature Tg of 77°C. Even at this Tg, the response time was less than one second.
A low cost technique based on the UV-VIS absorption spectroscopy is presented for the quality control of the spirit drink known as tequila. It is shown that such spectra offer enough information to discriminate a given spirit drink from a group of bottled commercial tequilas. The technique was applied to white tequilas. Contrary to the reference analytic methods, such as chromatography, for this technique neither special personal training nor sophisticated instrumentations is required. By using hand-held instrumentation this technique can be applied in situ during the production process.
Erbium doped, SiO2 - TiO2 powders were fabricated using the sol gel technique. The Er3+ concentrations were 2%, 5% and 10% (mol), and 10%, 25%, 50%, 70% for the TiO2. A strong, green up-conversion luminescence was found in the samples when exciting at 1532 nm and 978 nm. The recorded spectra showed less intense emissions at 410 nm and 675 nm. The excitation and emission mechanisms proposed were supported on experimental results, such as the absorption and emission spectra, the decay times and the luminescence intensity versus pump power.
Charge transport phenomena in semiconducting doped polymers is very important due to their spread use in xerography, electroluminescent devices (OLED's), photovoltaic cells and photorefractive systems. The carrier mobilities were determined by time-of-flight (TOF) measurements on indium-tin oxide/polymer composites/indium-tin oxide samples. Data are collected as a function of different external applied fields at various temperatures and are analyzed according to the disorder formalism.
Nanocrystalline yttrium aluminum garnet doped with Cerium (YAG:Ce3+), was synthesized by means of a modified sol-gel method that consists of a mixture of salts in an aqueous media. Structure and morphology were characterized by X-ray diffraction and Transmission Electron Microscopy. Single crystalline phase were obtained and the crystallite size range from 26 nm to 96 nm depending on the annealing temperature (from 800 to 1150 °C, respectively). The photoluminescence dependence on the crystallite size and ion concentration was performed. The experimental results show that the best ion concentration where the highest luminescence was obtained correspond to 0.1 mol% and that increases as the crystallite size increases. The feasibility of the modified sol-gel method for the preparation of nanocrystalline YAG is discussed.
We describe a tunable, narrow-band, coherent THz radiation source based on parametric down-conversion in a photonic crystal. Our design is based on down-conversion mixing and a local-field enhancement mechanism that is available by tuning each of the two driving laser fields either to band-edge or to a defect mode in the band gap. The frequency of the down-converted signal can be tuned by intersecting two non co-linear laser sources. The polarizations are degenerate at
normal incidence and have sub-THz down-conversion maximum. The peak conversion efficiency for both polarizations is enhanced by over two orders of magnitude.
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.
We analyze linear and no linear optical properties of PMMA clusters in thin film s with Ni nanoparticles dispersed with different concentrations. Saturable absorber and negative nonlinear refraction index behavior evidences were found using z-scan technique. We also show that these properties have not dependence of the type of matrix but they have on concentration.
Most of the optics measurements techniques used generate interferograms as a result. These give us information about the object's quality, surface, etc. Evaluating and knowing the heat gradient of an object, is a typical application of the interferograms analysis. We know that if we subject an object to heat, this will generate interferograms, in which the fringes form will be temporal, the deformation of the fringes tel us the temperature gradient, but it doesn't give us the temperature level of the object. In order to obtain this level we sampled interferograms in different intervals and we count the number of fringes in every sample interferogram. With this process we make a characterization that provide the temperature level change in an object. In order to acquire the interferograms we used the National Instruments IMAQ-1408 board and the software was designed in LabView.
We have developed a program for phase shift measurement on fringes pattern. Our program has capability to measure displacement of vertical fringes, tilted, curvy, and circular fringes, because of the use of pattern correlation.
New faster detection systems have allowed better measurements of complex fluorescence decays for active ions in laser crystal materials. We have measured a fluorescence decay that shows a fast initial decay followed by a non- exponential behavior that cannot be described satisfactory by most standard models for nonradiative energy transfer process. With current models it is customary to consider three characteristic temporal stages for the luminescent decay: (1) an exponential decay that is described by the first order approximation of the corresponding model at very short times, (2) a non-exponential decay described by the model at intermediate times, and (3) an exponential decay at later times determined by the migration excitation among donor ions. A new model is presented to account for the donor transient with no temporal stages. The master equations are solved in an analytical and exact form. This modeling allows us to consider any sum of interactions to drive the direct energy transfer. The discreetness of the crystal lattice is not neglected and it is taking into account the actual random distribution of activators around each donor. By using our modeling we are able to predict the measured fluorescence decay of the 4F3/2 state of the Nd+3 in Nd(1.5%),Er(20%):YSGG.
The radiative characteristics of sol-gel glasses doped with quinine sulphate are investigated to study the effects of the porous matrix upon the absorption and fluorescence spectra. The broadening of the spectra is explained in terms of an inhomogeneous distribution of the adsorbed molecules into the porous glass. This inhomogencous distribution is produced by the attachment of the molecules to the substrate in a non-planar fashion or on distorted sites, for this reason each emitting center relaxes with its own characteristics.
Quantum yields of sol-gel glasses and PMMA/sol-gel composites doped with quinine sulphate are measured and the improvement in quantum yield by the samples, in comparison with the molecules in ethanol, is interpreted as a reduction of nonradiative channels by the isolation of the molecules by the cage of the glass.
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