Dye Films Research Articles

Photoluminescence of high optical quality CdS:Dy thin films deposited by close-spaced vacuum sublimation

CdS:Dy polycrystalline films were deposited by close-spaced vacuum sublimation (CSVS) method using glass slides as substrates. The films are highly dispersed with the grain size from smaller than 0.1 μm to 1.0 μm. The CdS:Dy films are n-type and only correspond to single wurtzite phase. The crystallites are preferentially oriented with (002) planes parallel to the substrate surface. Analysis of PL spectra, caused by the emission of donor-acceptor pairs lets us determine the nature and energy structure of the intrinsic defects and residual impurities in the films. It is important to note that the PL and reflection spectra observe the narrow lines of bound and free excitons. This allows us to found bandgaps of these films quite accurately. A correlation between optical and structural properties was established. The results of the structural and PL measurements showed that the CdS:Dy polycrystalline films are of highly crystal and optical quality.

Intrinsic and photo-induced properties of high refractive index azobenzene based thin films [Invited

We explore the limits of the photosensitive response of thin, 15 to 35 nm, films of complex azobenzene dyes. They show high refractive index, reaching 1.8, and significant photo-induced birefringence. We have successfully recorded strong, birefringent phase gratings with visible light and used the diffraction efficiency measurements to monitor their temporal evolution. The photo-induced gratings in such thin films were found not to be associated with any periodic surface relief, a typical feature in thicker azobenzene layers.

Plasmon-enhanced light absorption at organic-coated interfaces: collectivity matters

Intermolecular interactions in thin films of organic dyes control the enhancement of the optical absorption by collective plasmons of gold nanoparticles.

Remote and portable mechanoluminescence sensing system based on a SrAl2O4:Eu,Dy film and its potential application to monitoring the safety of gas pipelines

This paper describes the development of an entirely remote, portable, and low-cost sensor system that includes a mechanoluminescence (ML) sample, optical sensor, and wireless data transmitter module. A composite consisting of SrAl2O4:Eu,Dy and epoxy resin was used as the ML test sample. The performance of the ML system, including the wireless function and accuracy, were tested under laboratory conditions. The wireless module was confirmed to provide reliable synchronous data transmission. The ML sensor system was then utilized to measure the stress of an object in a practical application. The ML data were easily acquired even with an applied load of 300 N and eventually stabilized with continuous load cycles. The ML system was able to detect a crack in a gas pipeline during operation with high sensitivity. The combined results indicate that the designed ML sensor system can potentially be applied as a smart and wireless structural health monitoring system.

Efficiency enhancement of natural dye sensitized solar cell by optimizing electrode fabrication parameters

AbstractEfficiency of dye-sensitized solar cell (DSSC) depends on several interrelated factors such as type and concentration of dye, type and thickness of photoelectrode and counter electrode. Optimized combination of these factors leads to a more efficient cell. This paper presents the effect of these parameters on cell efficiency. TiO2nanoporous thin films of different thicknesses (5 μm to 25 μm) were fabricated on indium doped tin oxide (ITO) coated glass by doctor blading method and characterized by inverted microscope, stylus surface profiler and scanning electron microscope (SEM). Natural organic dye of different concentrations, extracted from turmeric, was prepared with ethanol solvent. Different combinations of dye concentrations and film thicknesses along with different types of carbon catalyst have been investigated by I-V characterization. The result shows that the cell made of a counter electrode catalyst material prepared by candle flame carbon combined with about 15 μm thick photoelectrode and 100 mg/mL dye in ethanol solvent, achieves the highest efficiency of 0.45 %, with open circuit voltage of 566 mV and short circuit current density of 1.02 mA/cm2.

Rapid Microwave-Assisted Self-Assembly of a Carboxylic-Acid-Terminated Dye on a TiO2 Photoanode

Self-assembly of carboxylic-acid-functionalized dyes on mesoporous, anatase TiO2 is at the heart of dye-sensitized solar cells (DSSCs). However, the process often requires 6–20 h of electrode immersion at room temperature in the dye-bath solutions. Here, we introduce a new, rapid microwave-assisted sensitization technique (MWAS), which significantly accelerates the sensitization process and yields high-quality, self-assembled films of an organic dye within 5 min. Targeted experiments show that the effects of the microwave radiation cannot be explained purely on the basis of the thermal component. The interaction of the microwave radiation with the conductive fluorine-doped tin oxide (FTO) electrical contact is a key aspect to consider and a unique feature of MWAS that is the likely cause for producing rapid self-assembly of the dye on the surface.

Structural and Optical Properties of New Poly vinyl Alcohol Grafted Methyl Red (PVA-g-MR)

New polymeric dye films have been synthesised by condensation polymerization and reaction polyvinyl alcohol with methyl red dye to produce a new graft copolymer (PVA-g-MR) .The structural properties of these samples were investigation by FTIR and XRD .The FTIR spectra indicated the important functional groups for polymer and dye ,The peak at 1708cm-1 related to carbonyl groups indicated the correct reaction between PVA and dye. XRD investigation indicated the crystalline structure to new polymer .Optical parameters have been studied by preparing thin films on glass substrates using cast technique. Many optical parameters have been calculated depending on absorption and reflective spectra in the wavelength range (300-1000)nm , such as refraction index n(1.58) , absorption coefficient α , optical energy gap Eg (2.05eV), dielectric constant (2.52), Urbach tail (186meV) and real and imaginary part of dielectric constant , Surface energy(SELF) and volume energy loss(VELF) were also investigated by depending on real and imaginary parts of dielectric constant .It is clear that the value of VELF greater than the peak of SELF ,it is also clear that of SELF and VELF around energy region 2.35eV and 2.5eV respectively. Optical ,electrical conductivities (σopt , σe ) were also investigate , σopt increasing by increased the photon energy related to strong absorption .The results satisfied Wimple –Dideminco formula .Optical parameters of (PVA-g-MR) are useful to make the materials a prominent one for solar cell applications.

Dielectric broadband meta-vector-polarizers based on nematic liquid crystal

Polarizer, as an indispensable optical element, has been widely used in various optical systems, which splits a beam into two beams of orthogonal linear polarizations. Due to the appearance of the vector optical field (VOF) and its unique properties, the vector polarizer also meets the requirement in a wide variety of applications. Here we present and demonstrate the realization of dielectric broadband vector polarizer, being in fact a liquid-crystal-based space-variant uniaxial crystal (LC-SV-UAC), which is made by a wedged thin cell adhered with space-variant photo-aligned dichroic dye films and filled with the nematic liquid crystal with a thickness of tens of microns. The vector polarizer works based on the birefringent mechanism to spatially separate the orthogonally polarized ordinary and extraordinary beams. The vector polarizers via a LC-SV-UAC have the advantages of mass-production and easy fabrication of large-size and complex structures. In particular, the high-performance broadband vector polarizers we presented and fabricated can not only flexibly tailor the polarization structures and the intensity patterns of optical fields but also act as a high-efficiency generator of VOF, and a key element for realizing the VOF laser and for fabricating the novel photon states in the future.

Polymeric Dye Film Deposition in Vacuum

Polymeric Dye Film Deposition in Vacuum

Phase, microstructural analysis, and humidity-sensing properties of orange dye and cuprous-oxide composite

The effect of humidity on the phase, microstructure, and electrical properties of an organic compound orange dye (C17H17N5O2) and cuprous-oxide (Cu2O) micro-composite thin film has been investigated. 5 wt% commercially available orange dye and 30–40 wt% Cu2O were used to prepare an aqueous solution. The solution was layered in the form of a thin film on a pre-deposited copper glass substrate using a drop-casting technique under normal gravity conditions. A gap was made in the middle of the surface to get ohmic type electrodes at the ends of the glass substrate. In this way, a Cu/Cu2O–OD/Cu humidity sensor was fabricated. A self-made setup was used to carry out the experiment. Impedance of these samples was observed to decrease by 57–84 times and capacitance increased by 20–26 times with an increase in humidity from 62 to 98% RH. These observations demonstrated that impedance was more sensitive to the variations in humidity as compared to capacitance.

Optical properties and photoinduced aggregation of cyanine dyes on silver island films

The optical properties and photoinduced modification of hybrid nanostructures, which are silver island films coated with a layer of cyanine dye, were studied. Experiments were conducted on three dye homologs and films differing in the equivalent thickness of the deposited silver. It was shown that the absorption of a hybrid film is not the sum of the absorption of the molecular layer and the plasmon absorption of the silver. The near fields of nanoparticles (NPs) that form island films increase the absorption of organic molecules, with the greatest increase observed in the band of J-aggregates. The influence of the near fields can be reduced by distancing the molecules from the NPs using an insulating polymer layer. In the presence of silver NPs, the photoinduced modification of the component composition of the layers of the dyes occurs at far lower energy densities. Resonant nanosecond laser pulses lead to the aggregation of molecules in hybrid films.

Strongly Red-Shifted Photoluminescence Band Induced by Molecular Twisting in Cyanine (Cy3) Dye Films

Cyanine dye molecules, used as monomers or in aggregate form, find interesting applications in optoelectronic devices. Among the various aggregate species incorporating organic dyes, centrosymmetric dimers are known as nonluminescent. They can act as exciton quenchers due to a low-energy optically forbidden excited state. In this study, however, we show that a dimer species in thin films exhibits efficient and strongly red-shifted photoluminescence. When the films were excited, a monomer emission at 590 nm along with a second emission peak at 680 nm was observed. A close relation between the dye concentration and the emission showed that a new emission at 680 nm corresponds to the dimer emission. Circular dichroism (CD) spectroscopy reveals that a fraction of the dimers exist in a twisted dimer configuration. Stable, long-lived, and quenchable fluorescence with high quantum yield is attributed to this dimer emission.

Microcavity Laser Based on a Single Molecule Thick High Gain Layer.

The ability to confine excitons within monolayers has led to fundamental investigations of nonradiative energy transfer, super-radiance, strong light-matter coupling, high-efficiency light-emitting diodes, and recently lasers in lateral resonator architectures. Vertical cavity surface emitting lasers (VCSELs), in which lasing occurs perpendicular to the device plane, are critical for telecommunications and large-scale photonics integration, however strong optical self-absorption and low fluorescence quantum yields have thus far prevented coherent emission from a monolayer microcavity device. Here we show lasing from a monolayer VCSEL using a single molecule thick film of amphiphilic fluorescent dye, assembled via Langmuir-Blodgett deposition, as the gain layer. Threshold was observed when 5% of the molecules were excited (4.4 μJ/cm2). At this level of excitation, the optical gain in the monolayer exceeds 1056 cm-1. High localization of the excitons in the VCSEL gain layer can enhance their collective emission properties with Langmuir-Blodgett deposition presenting a paradigm for engineering the high gain layers on the molecular level.

Structural and magnetic properties of Dy-implanted GaN films

GaN:Dy films were prepared by implanting Dy ions into c-plane (0001) GaN films and a subsequent rapid thermal annealing process. The structural and magnetic properties of samples were investigated by means of X-ray diffraction (XRD), Raman and Physical Property Measurement System (PPMS). The XRD and Raman studies showed that lattice damage and dislocation caused by ion implantation can be effectively recovered by rapid thermal annealing. The PPMS results showed ferromagnetism at room temperature. The average value of the moment per Dy ion (Ms/Dy) is increased after thermal annealing. The available vacancies and formation of bound magnetic poloron as a result of implantation and thermal annealing are assigned responsible for observed ferromagnetism.

Intermolecular states in organic dye dispersions: excimers vs. aggregates

Efficient energy transfer in dispersed films of organic dyes to dark excimer sites and highly emissive J-coupled dimers.

Design, synthesis and photoisomerization behavior of novel azobenzene-based dyes containing different alkyl chains and isolation groups

A series of reactive azo dyes based on 4-phenylazophenol, containing hexenyloxy-, allyloxy-ethoxy-propoxy- and tetramethyl-disiloxanyl-propoxy substituents were synthesized. Additionally, allyl-functionalized azo-based chromophores with changeable isolation groups (hydroxymethylene-, trimethylsiloxymethylene- and pentafluorophenoxymethylene-) as well as with an additional azobenzene unit were successfully obtained. The photoisomerization behaviors of the synthesized azo dyes were investigated in solution as well as in films. Importantly, the occurrence of photoisomerization (at least near the surface after UV treatment) was confirmed in the crystalline dye films. The resulting compounds can be employed for the synthesis of a wide variety of azo-based materials which may be suitable for optical and electrooptical applications.

Effect of Concentration Ratio of Precursor-Surfactant Solution on The Performance of Boron-doped ZnO Nanotubes Dye Sensitized Solar Cells

Boron doped zinc oxide (ZnO) nanotubes have successfully been grown using seed-mediated hydrothermal method at various concentrations of precursor-surfactant solution. The growth of ZnO nanotubes was carried out at a temperature of 90°C for 8 hours and a drop in temperature to 50°C for 16 hours. In this study, the effect of concentration ratio of precursor-surfactant was evaluated. Samples were characterized using UV-Vis Spectroscopy, X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray (EDX). UV-Vis spectra of the samples showed that the ZnO nanotubes were grown on the Flourine Tin Oxide (FTO) and the strong absorption occurred in the wavelength range of 300-400 nm, which is typical spectrum for hexagonal-nanostructure. XRD patterns showed five diffraction peaks at 2θ = 32.05°, 34.5°, 36.35°, 47.75° and 56,9°. The analysis of EVA Diffrac Plus confirmed the peaks were represented to the lattice of (100), (002), (101), (102), and (110) respectively. FESEM images of the samples showed the hexagonal-shaped ZnO nanotubes with an average diameter of 50-340 nm and an average thickness of 1.2 - 4.4 μm observed for all samples. Uniformity the size and shape of ZnO nanotubes become higher as concentrations of ZNH decreased. The EDX spectra of the samples showed the percentage of weight of Zn, O, and B was 69.35%, 21.60% and 4.76% respectively, while the percentage of their atoms was 33, 06%, 42.08% and 13.71% respectively. The B-doped ZnO nanotubes solar cells were fabricated by arranging a sandwich structure, consisting of the FTO, ZnO nanotubes, dye, electrolyte and platinum thin film. I-V characteristics of cell were carried out under irradiation of 100 mWcm<sup>-2</sup> halogen lamp. The I-V curves produced the highest efficiency from the cells utilizing the B-doped ZnO nanotubes with their concentration ratio of precursor-surfactant of 0.1 M : 0.04 M as the active material, which was 0.352%. This value is much higher than that of pure ZnO nanotube based DSSC of 0.05%.

Effect of Concentration Ratio of Precursor-Surfactant Solution on The Performance of Boron-doped ZnO Nanotubes Dye Sensitized Solar Cells

Boron doped zinc oxide (ZnO) nanotubes have successfully been grown using seed-mediated hydrothermal method at various concentrations of precursor-surfactant solution. The growth of ZnO nanotubes was carried out at a temperature of 90°C for 8 hours and a drop in temperature to 50°C for 16 hours. In this study, the effect of concentration ratio of precursor-surfactant was evaluated. Samples were characterized using UV-Vis Spectroscopy, X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray (EDX). UV-Vis spectra of the samples showed that the ZnO nanotubes were grown on the Flourine Tin Oxide (FTO) and the strong absorption occurred in the wavelength range of 300-400 nm, which is typical spectrum for hexagonal-nanostructure. XRD patterns showed five diffraction peaks at 2θ = 32.05°, 34.5°, 36.35°, 47.75° and 56,9°. The analysis of EVA Diffrac Plus confirmed the peaks were represented to the lattice of (100), (002), (101), (102), and (110) respectively. FESEM images of the samples showed the hexagonal-shaped ZnO nanotubes with an average diameter of 50-340 nm and an average thickness of 1.2 - 4.4 μm observed for all samples. Uniformity the size and shape of ZnO nanotubes become higher as concentrations of ZNH decreased. The EDX spectra of the samples showed the percentage of weight of Zn, O, and B was 69.35%, 21.60% and 4.76% respectively, while the percentage of their atoms was 33, 06%, 42.08% and 13.71% respectively. The B-doped ZnO nanotubes solar cells were fabricated by arranging a sandwich structure, consisting of the FTO, ZnO nanotubes, dye, electrolyte and platinum thin film. I-V characteristics of cell were carried out under irradiation of 100 mWcm<sup>-2</sup> halogen lamp. The I-V curves produced the highest efficiency from the cells utilizing the B-doped ZnO nanotubes with their concentration ratio of precursor-surfactant of 0.1 M : 0.04 M as the active material, which was 0.352%. This value is much higher than that of pure ZnO nanotube based DSSC of 0.05%.

Optical constants and nonlinear calculations of fluorescein/FTO thin film optical system

The organic thin films of fluorescein dye were deposited on fluorine-doped tin oxide glass substrate by using low-cost spin coating technique. The surface of the deposited film was characterized by using AFM and X-ray diffraction spectroscopy, which shows that the film is uniform and amorphous. The spectrophotometric study was carried out at the wavelength range of 300–2500nm. The spectral dependences of the linear refractive index and absorption index were found to decrease as the wavelength was increased. Tauc's plot study revealed that the film shows the direct transition and energy band gap values were found 1.75eV and 3.55eV for the thin film and the substrate, respectively. Optical constants were found nearly the same in the higher energy domain (1.0–4.5eV). Spectroscopic method was employed to study the nonlinear optical susceptibility χ(3). The deposited thin film is a promising optical system for new generation of optoelectronics.

Dy uniform film morphologies on graphene studied with SPA-LEED and STM

The use of graphene for microelectronics and spintronic applications requires strategies for metals to wet graphene and to grow layer-by-layer. This is especially important when metals will be used as electrical contacts or as spin filters. Extensive work in the literature so far has shown that this is very challenging, since practically all metals grow 3D, with multi-height islands forming easily. Reasons for the 3D morphology are the much weaker metal carbon bond when compared to the metal cohesive energy and the role of Coulomb repulsion of the poorly screened charges at the metal graphene interface. We employed the complementary techniques of SPA-LEED and STM to study the growth of Dy on graphene. It was found that under kinetic limitations it is possible to fully cover graphene with a bilayer Dy film, by growing well below room temperature in stepwise deposition experiments. The Dy film, however, is amorphous but ways to crystallize it within the 2D morphology are possible, since long range order improves at higher growth temperature.