Blended Host Research Articles

Optimization and investigation polyvinyl pyrrolidone/polyacrylamide (PVP/PAM) blend electrolytes via optimal mixture design

In this paper, polymer blend electrolytes (PBEs) composed of polyvinyl pyrrolidone/polyacrylamide blend hosts (PVP/PAM) and sodium chloride salt (NaCl) were prepared via solution casting techniques and their ionic conductivity was optimized. PBEs with the maximum conductivity were characterized using FTIR, TGA, LSV, and CV to investigate the interactions between the polymer blend host and the salts, the thermal stability and electrochemical window potential stability of the optimized PBEs. Moreover, PBEs were characterized by electrochemical impedance spectroscopy to investigate their ionic conductivity. The FTIR analysis showed that NaCl has been complexed with PVP/PAM blend host. It was found that the conductivity of PBEs were strongly dependent on the concentrations of salts and polymer blend hosts. The conductivity of the PBEs boosted with the increase in salt concentration up to its optimal concentration but the reverse is true in the case of polymer blend host concentrations. The PBEs composed of 86.5 wt% of PVP/PAM and 13.5 wt% of NaCl exhibited an appreciable conductivity of 1.722 × 10−6 S/cm at ambient temperature, which is close to the predicted conductivity of 1.766 × 10−6 S/cm. The dielectric constant and loss of the PBEs increased with the increase in salt concentrations up to their optimum content. The optimized PBEs did not exhibit oxidation and reduction peaks in the range of -3 V–3 V window potential at 25 °C and are thermally stable up to 240 °C. Hence, the electrochemical performance and thermal stability of the PBEs demonstrated that the PBEs could be employed as electrolytes for sodium batteries.

Effective exciplex host for solution-processed narrowband blue TADF-OLEDs using a 9-(dibenzo[b,d]thiophen-2-yl)-9H-carbazole analogue with an adamantane substituent

Implementing an exciplex host system in the emitting layer is crucial for achieving highly efficient thermally activated delayed fluorescence (TADF) and phosphorescent organic light-emitting diodes (OLEDs). In this study, we successfully designed and synthesized 3-((3r,5r,7r)-adamantan-1-yl)-9-(dibenzo[b,d]thiophen-2-yl)-9H-carbazole (AdCz-DBT) and 9-(dibenzo[b,d]thiophen-2-yl)-9H-carbazole (Cz-DBT) as p-type hosts for the exciplex host implementation, and 7-(4-(tert-butyl)phenyl)-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (tPDBA) as an n-type host. The AdCz-DBT host incorporates a large and robust adamantane group into Cz-DBT, increasing molecular weight, film-forming properties and thermal stability. Additionally, AdCz-DBT maintains energy levels and photophysical properties similar to those of adamantane-free Cz-DBT. Efficient exciplex emission was observed in the blend film due to well-matched energy levels of the synthesized p- and n-type hosts. The introduction of adamantane into Cz-DBT did not hinder exciplex formation, resulting in a relatively high photoluminescence quantum yield and improved charge balance in the mixed host with tPDBA.Ultimately, the solution-processed blue TADF-OLED with the AdCz-DBT:tPDBA blend host demonstrated a relatively high external quantum efficiency of 8.00% and a long operational lifetime, exhibiting excellent performance compared to devices using the Cz-DBT:tPDBA blend host.

Mild and Efficient Extraction of Fluorescent Chlorophyll a from Spinach Leaves for Application as the Sustainable Emitter in Light‐Emitting Electrochemical Cells

AbstractNatural pigments are sustainable compounds that can be employed as emitters, sensors and sensitisers in optoelectronics. The most abundant pigment, chlorophyll, offers advantages of easily available and plentiful feedstock, biodegradability and non‐toxicity. However, strenuous extraction and separation limit its application on larger scale. In this work, a practically mild and scalable extraction and separation method for rapid isolation of chlorophyll a from spinach is presented. Three different stationary phases for column chromatography were evaluated, and a new solvent system was developed for the elution of chlorophyll a on a neutral alumina chromatography column. The purified product was obtained with a yield of 0.98 mg ⋅ g−1 with respect to the dry leaves. A first light‐emitting electrochemical cell (LEC) based on chlorophyll a as the emitter is reported, using the extracted chlorophyll a as the guest compound dispersed in a blend‐host matrix in a concentration of 2.5 or 5 mass %. The higher‐chlorophyll‐concentration LEC exhibits emission solely from the chlorophyll emitter, with the main emission peak located at 675 nm. The lower‐chlorophyll‐concentration LEC features two distinct emission bands, one in the red region that is originating from the chlorophyll guest and one in the blue region (main peak at 430 nm) that stems from the blend host. This combined red:blue emission can be attractive for, e. g., greenhouse applications, since it matches the action spectrum of plant photosynthesis.

Synergistic effect of polymer blend compositions on the structural, thermal, optical, and broadband dielectric properties of P(VDF-HFP)/PEO/ZnO polymer nanocomposites

Polymer nanocomposites (PNCs) composed of poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP))/ poly(ethylene oxide) (PEO) blend host matrix of varying compositions i.e., xP(VDF-HFP)/(100–x)PEO with x values 20, 50, and 80 wt%, and zinc oxide (ZnO) as nanofiller (2 wt%) are prepared by state-of-the-art homogenized solution cast method. The SEM micro-images of these PNC films revealed that the polymer blend compositions considerably affect the polymers miscibility, spherulitic morphologies, and crystalline phases. FTIR spectra demonstrated that the P(VDF-HFP) and PEO chain interactions in these PNCs change significantly with the polymer blend compositions. The DSC results revealed a decrease in PEO crystallite temperature and degree of crystallinity with the increase of P(VDF-HFP) amount in the blend matrix of these PNC materials. Analysis of UV-Vis spectra categorized these PNCs of wide band gap (∼ 3.1 eV) semiconductive optical materials. Broadband frequency range (20 Hz–1 GHz) dielectric dispersion demonstrated that 50P(VDF-HFP)/50PEO-2 wt% ZnO composition based nanodielectric film has a relatively high dielectric constant, whereas the chain segmental and dipolar reorientation relaxation processes are strongly polymer blend composition dependent for these PNC materials. The experimental results are discussed in detail concerning the multifunctionality of these PNCs as promising candidates for innovation in flexible optoelectronic and nanodielectric-based microelectronic devices.

Introducing MR‐TADF Emitters into Light‐Emitting Electrochemical Cells for Narrowband and Efficient Emission

AbstractOrganic semiconductors that emit by the process of multi‐resonance thermally activated delayed fluorescence (MR‐TADF) can deliver narrowband and efficient electroluminescence while being processable from solvents and metal‐free. This renders them attractive for use as the emitter in sustainable light‐emitting electrochemical cells (LECs), but so far reports of narrowband and efficient MR‐TADF emission from LEC devices are absent. Here, this issue is addressed through careful and systematic material selection and device development. Specifically, the authors show that the detrimental aggregation tendency of an archetypal rigid and planar carbazole‐based MR‐TADF emitter can be inhibited by its dispersion into a compatible carbazole‐based blend host and an ionic‐liquid electrolyte, and it is further demonstrated that the tuning of this active material results in a desired balanced p‐ and n‐type electrochemical doping, a high solid‐state photoluminescence quantum yield of 91%, and singlet and triplet trapping on the MR‐TADF guest emitter. The introduction of this designed metal‐free active MR‐TADF material into a LEC, employing air‐stabile electrodes, results in bright blue electroluminescence of 500 cd m−2, which is delivered at a high external quantum efficiency of 3.8% and shows a narrow emission profile with a full‐width‐at‐half‐maximum of 31 nm.

Optical characterization of PVDF/PMMA/OMMT hybrid polymer nanocomposite films for futuristic optoelectronic devices

Hybrid polymer nanocomposite (HPNC) films based on poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend (80/20 wt/wt%) host matrix and organo-modified montmorillonite (OMMT) nanoclay filler (concentrations 0.0, 2.5, 5.0, and 10 wt%) are prepared by the homogenized solution casting method. The X-ray diffraction (XRD) and scanning electron microscopic (SEM) studies revealed the formation of intercalated and exfoliated OMMT structures in the prepared composites. The detailed optical characterization of these HPNC films is carried out with measurements of absorbance spectra by employing a dual beam ultraviolet-visible (UV-Vis) spectrophotometer of wavelength range 200–800 nm. The varying amounts of dispersed OMMT into the PVDF/PMMA blend matrix leads to a gradual decrease in the direct energy band gap of the host matrix from 5.12 eV to 4.54 eV and also shows semiconductive characteristics of 3.83 eV wide band gap at higher nanofiller concentrations. The band gap values of these HPNC films are compared and discussed with other composites of different polymer blend matrices dispersed with a variety of nanofillers. The increase of OMMT concentrations enhanced the range of refractive index (1.85–2.65), extinction coefficient (1.14–10.69 × 10–4), optical range dielectric permittivity (3.44–7.07), and optical conductivity (1.32–17.14 × 1011 s−1) of these HPNC films, at a fixed wavelength of 500 nm, which further changes largely with the alteration in wavelength of incident photons. The nanofiller concentration controllable optical parameters of these PVDF/PMMA/OMMT based HPNCs reveal that they could be promising performance and multipurpose optical materials in the advances of futuristic flexible-type optoelectronic devices.

Broadband dielectric behaviour and structural characterization of PVDF/PMMA/OMMT polymer nanocomposites for promising performance nanodielectrics in flexible technology advances

Characterization of broadband dielectric behaviour of polymer nanocomposites (PNCs) is vital for the exploration of efficient nanodielectrics as energy storage, flexible dielectric substrates, and insulators in a wide range of advanced electronic device technologies. Accordingly, herein, PNC films based on poly(vinylidene fluoride) (PVDF)/ poly(methyl methacrylate) (PMMA) blend matrix (80/20 wt/wt%) dispersed with 0, 2.5, 5, and 10 wt% organo-modified montmorillonite (OMMT) nanoclay are developed by state-of-the-art homogenized solution casting method. These PVDF/PMMA/OMMT compositions based flexible PNC films are characterized in detail by employing a scanning electron microscope (SEM) equipped with energy dispersive x-ray (EDX) device, x-ray diffractometer (XRD), Fourier transform infrared (FTIR) spectrometer, differential scanning calorimeter (DSC), inductance-capacitance-resistance (LCR) meter, and impedance/material analyzer (IMA). The SEM microimages, XRD traces, and FTIR spectra evidenced appreciable homogeneity and surface morphology, intercalated and exfoliated OMMT structures, and the α, β and γ-phase crystallites of the PVDF in these complex semicrystalline PNCs. The DSC thermograms confirmed a significant alteration in the melting temperature and degree of crystallinity of the PVDF crystallites with the increased amount of OMMT in the 80PVDF/20PMMA blend host matrix. The broadband dielectric dispersion spectra over the frequency range of 20 Hz−1 GHz explained the contribution of interfacial polarization in the complex dielectric permittivity at lower experimental frequencies, whereas at higher frequencies permittivity is ruled by dipolar polarization in these composites at 27 °C. The dielectric loss angle tangent and electric modulus spectra revealed an intense structural dynamics relaxation process in the upper radio frequency region. The influence of OMMT concentration on the dielectric permittivity and electrical conductivity is explored. The detailed dielectric and electrical characterization of these innovative semicrystalline composites with important structural and thermal properties revealed their immense potential as high-performance nanodielectrics for highlighting current applications of broadband frequency range electrical and electronic device technologies.

Thermal and dielectric properties of PVDF/PEO/SiO2 nanodielectrics for flexible radioelectronic device technologies

Hybrid polymer nanocomposites (HPNCs) are innovative multifunctional materials, which are developed and intensively studied for their uses in the rapid evolution of flexible and lightweight device technologies. Accordingly, to contribute in this area, thermal properties of the crystal phases and the broadband radio frequencies dielectric dispersion and relaxation behaviour of the HPNC films based on poly(vinylidene fluoride) (PVDF)/poly(ethylene oxide) (PEO)/silica (SiO2) are formulated and studied by employing differential scanning calorimeter (DSC) and impedance/material analyzer (IMA). DSC thermograms of these semicrystalline HPNCs explained the wide range alteration in the crystals melting temperature of PVDF (153–167 ​°C) and PEO (59–72 ​°C) and the total degree of crystallinity (4–87%) with varying compositional ratio over the entire range of the PVDF/PEO blend host matrix and the dispersed amount of amorphous SiO2 nanomaterial up to 15 ​wt%. The dielectric dispersion behaviour of these HPNCs, at 20 ​°C, confirmed a non-linear decrease in permittivity with the increase of applied radio wave electric field frequency from 1 ​MHz to 1 ​GHz, which lies in the range of 6 to 2. At a fixed frequency, dielectric permittivity values exhibited an uneven variation with the increase of SiO2 amount and also the modification in the composition of polymer blend matrix in these composites. The analysis of dielectric loss spectra and relaxation processes revealed that these are low loss dielectrics and the presence of SiO2 nanoparticles in the polymer blend matrix impedes the chain segmental dynamics and the dipole reorientation. The electrical conductivity of these HPNCs enhanced in the range of 10−8 to 10−4 ​S/cm with the increase in frequency but it changed anomalously when the constituent amounts of the formulated composites are varied. The polymer crystals thermal properties and the dielectric and electrical conductivity dispersion behaviour of these materials are demonstrated with the consideration of polymer-polymer and polymer-nanoparticle hybrid interfaces and interactions. The experimental results evidenced the behaviour of PVDF/PEO/SiO2 films as tunable nanodielectrics with their compositions and could be used as insulator and dielectric substrate materials in the advances of flexible radioelectronics and energy storage devices.

Morphological, structural, optical, broadband frequency range dielectric and electrical properties of PVDF/PMMA/BaTiO3 nanocomposites for futuristic microelectronic and optoelectronic technologies

Polymer blend nanocomposite (PBNC) films consisted of fluoropolymer poly(vinylidene fluoride) (PVDF) and plexiglass polymer poly(methyl methacrylate) (PMMA) blend host matrix (fixed composition blend of PVDF/PMMA = 80/20 wt/wt%) with barium titanate (BaTiO3) ceramic nanofiller of varying concentrations (x = 0, 2.5, 5, 10, and 15 wt%) were prepared via a state-of-the-art solution-cast method. Scanning electron microscope (SEM) images evidenced high homogeneity of these PBNC films and a huge alteration in the spherulite morphology of the PVDF with the increase in dispersed BaTiO3 concentration in the polymer blend matrix. The X-ray diffraction (XRD) patterns identified the presence of electro-active polar β- and γ-phases of the PVDF crystallites in all the composite materials which are supported by the results of Fourier transform infrared (FTIR) spectra. The differential scanning calorimeter (DSC) thermograms explained the high melting temperature of these overlapped PVDF polymorphs and the degree of crystallinity altered anomalously with the variation of nanofiller concentration. The absorbance of ultraviolet-visible (UV-Vis) radiations enhanced while the direct energy band gap of the 80PVDF/20PMMA blend matrix and also the semiconducting BaTiO3 was found to decrease with the increased concentration of nanomaterial in the host polymer matrix. The ambient temperature broadband dielectric spectra covering the frequency range from 20 Hz to 1 GHz explain that the real part of complex dielectric permittivity reduced with a huge dispersion at higher radio frequencies where the dielectric loss tangent and electric modulus spectra exhibited an intense chain segmental relaxation process. The electrical conductivity of these PBNC films increased with frequency augmented and illustrated a small variation for different concentration composites. The experimental results demonstrated that these PVDF/PMMA/BaTiO3 films could be potential candidates for frequency tunable nanodielectric, electromagnetic interference shielders, a flexible dielectric substrate, thermal insulators, and bandgap regulated materials for futuristic microelectronic, capacitive energy storage, and optoelectronic technologies.

Thermal, mechanical, and AC electrical studies of PVA–PEG–Ag2S polymer hybrid material

Polymer hybrid films were prepared by solution casting technique, using polyvinyl alcohol–polyethylene glycol (PVA–PEG) blend host matrix as the organic component and Ag2S (in-situ formed) as the inorganic component. Differential scanning calorimetry (DSC) studies revealed the increased flexibility of polymer hybrid films, when compared to pure PVA–PEG blend film. Thermal stability of the hybrid film PPS3 (with AgNO3:Na2S ratio equal to 3.0 ml: 1.5 ml) which has uniformly distributed Ag2S nanostructures is more, when compared to other hybrid films, as revealed by thermogravimetric analysis (TGA). Polymer hybrid film PPS1 (with AgNO3:Na2S ratio equal to 1.0 ml: 0.5 ml) which has uniformly distributed Ag2S microstructures shows increased values of tensile strength and percentage elongation at break. The presence of Ag2S nanoparticles in PPS3 film has increased the overall toughness of the corresponding hybrid film. The highest bulk conductivity equal to 1.43 × 10–5 Sm−1 is observed for PPS4 film (with 4.0 ml: 2 ml ratio of precursors), which has a comparatively lower degree of crystallinity and porous structure. Impedance spectroscopy studies reveal that Ag2S filler, in its micro and nano forms, can substantially improve the AC conductivity and dielectric properties of PVA–PEG polymer blend (loaded with Ag2S).

Spectroscopic study of trivalent rare earth Sm3+ ions doped PVA + PEG blended polymer films

The concentration varied trivalent active lanthanide Sm3+ ions of 0–5 mol % doped complex miscible host polymer blends of Poly (vinyl alcohol) (PVA) and Poly (ethylene glycol) (PEG) were prepared by the universal solution casting technique and their spectroscopic characteristic features was examined through optical absorption and photoluminescence analysis. The optical absorption analysis of Sm3+ doped polymeric samples used for investigation and prediction of the optical parameters. The optical band gap energy (Eg) was evaluated from the Tau’c extrapolation and is found decreased with increasing Sm3+ ions concentration. From the photoluminescence analysis the high intense reddish orange emission peak at 595 nm corresponding to 4G5/2 → 6H7/2 transition was observed in under the 401 nm excitation wavelength which may be used as active laser medium. The decay curves of the polymer blends are exhibiting non exponential nature. The Life time and efficiency of the PVAEG: Sm3+ (5 mol %) complex blended polymer film is better and is acting as the prominent material for lasing applications and development of opto electronic devices. The present blended host polymer matrix doped with 5 mol % Sm3+ ions is a perfect suitable potential material for active reddish orange emission lasing materials for photonic applications and photo electronic devices.

Synergistic effects of salt concentration and polymer blend composition on the crystal phases, dielectric relaxation, and ion conduction in PVDF/PEO/LiCF3SO3 solid polymer electrolytes

Effects of lithium triflate (LiCF3SO3) salt concentration and compositional weight ratio of poly(vinylidene fluoride) (PVDF)/poly(ethylene oxide) (PEO) blend host matrix on the structural, dielectric relaxation, and ion transport properties of PVDF/PEO/LiCF3SO3 solid polymer electrolyte (SPE) films have been investigated. Variations in the amounts of constituents in these SPEs enormously alter the characteristic crystal phases of polymers and their chain segmental dynamics. Ionic conductivity increases by more than five orders of magnitude on loading LiCF3SO3 amount up to 30 wt% in the 75PVDF/25PEO blend matrix, and by about two orders with the increase of PEO amount from 25 to 90 wt% in the polymer blend host matrix of PVDF/PEO–25 wt% LiCF3SO3 films. Correlation between ionic conductivity and relaxation time confirms that the transport of ions is coupled to the polymer chain segmental motions in these SPEs. Total ion transference number, electrochemical voltage stability, and cyclic performance of these electrolyte materials are determined and appropriately explained.

Thermally activated delayed fluorescence with 7% external quantum efficiency from a light-emitting electrochemical cell

We report on light-emitting electrochemical cells, comprising a solution-processed single-layer active material and air-stabile electrodes, that exhibit efficient and bright thermally activated delayed fluorescence. Our optimized devices delivers a luminance of 120 cd m−2 at an external quantum efficiency of 7.0%. As such, it outperforms the combined luminance/efficiency state-of-the art for thermally activated delayed fluorescence light-emitting electrochemical cells by one order of magnitude. For this end, we employed a polymeric blend host for balanced electrochemical doping and electronic transport as well as uniform film formation, an optimized concentration (<1 mass%) of guest for complete host-to-guest energy transfer at minimized aggregation and efficient emission, and an appropriate concentration of an electrochemically stabile electrolyte for desired doping effects. The generic nature of our approach is manifested in the attainment of bright and efficient thermally activated delayed fluorescence emission from three different light-emitting electrochemical cells with invariant host:guest:electrolyte number ratio.

Blended host ink for solution processing high performance phosphorescent OLEDs

In order to solve the interface issues in solution deposition of multilayer OLED devices, a blended host concept was developed and applied to both spin-coating and inkjet printing of phosphorescent OLEDs. The blended host consists of 1,3-bis(carbazolyl)benzene (mCP) and1,3,5-tri(phenyl-2-benzimidazoly)-benzene (TPBi). Maximum current efficiency (CE) of 24.2 cd A−1 and external quantum efficiency (EQE) of 7.0% have been achieved for spin-coated device. Maximum CE and EQE of 23.0 cd A−1 and 6.7% have been achieved for inkjet printed device. The films deposited by printing and spin-casting were further researched to explore the effect of those different processing methods on device performance.

High brightness and efficiency of polymer-blend based light-emitting layers without the assistance of the charge-trapping effect.

Polymeric light-emitting materials have been developed recently as an attractive solution-processable alternative to conventional vacuum-deposited small molecules in organic/polymeric light-emitting diodes, but they are still limited in terms of their performance, especially with low luminance and efficiency. We report on some noteworthy characteristics of a new type of single emitting layer (EML), composed of a blend of a host blue-emitting polyspirobifluorene-based copolymer and a guest yellow-emitting poly(p-phenylene vinylene) derivative copolymer. These host and guest polymers have nearly identical highest occupied molecular orbital levels of about 5.2 eV, and lowest unoccupied molecular orbital levels of about 2.4 eV and 2.9 eV, respectively, minimizing the prevailing charge-trapping properties of their blend. Even in the absence of the charge-trapping effect, it is shown that very bright green electroluminescent (EL) emission with a maximum luminance of ~142,000 cd/m2 can be realized for the blended host:guest EML at a moderate concentration (~5 wt%) of the guest polymer. Current efficiency is also observed to be up to ~14 cd/A, which is much higher than those (3.6~5.1 cd/A) of reference devices with pure host or pure guest polymeric EMLs. Moreover, there is a small change in green color emission, with CIE coordinates of (0.35, 0.60) even at high luminance, showing good color stability of the EL emission from the blended EML. These significant improvements in device performance are mainly attributed to efficient Förster resonance energy transfer between the host and guest polymers in the blended EML. Together with its simple structure and easy processability, the high brightness and efficiency of our blended polymeric EML provides a new platform for the development of solution-processable light-emitting devices and/or advanced emissive display devices.

Preparation and characterization studies of PMMA–PEO-blend solid polymer electrolytes with SiO2 filler and plasticizer for lithium ion battery

Solid polymer electrolyte systems comprising of polyethylene oxide (PEO) and polymethyl methacrylate (PMMA) as blended polymer host, lithium trifluoromethanesulfonate (LiCF3SO3) as dopant salt, ethylene carbonate (EC) as plasticizer, and silicon dioxide (SiO2) as inorganic filler were prepared by solution casting method. PMMA–PEO–EC–LiCF3SO3–SiO2-blend solid polymer electrolytes were prepared to study the blending effect of PMMA into PEO solid polymer electrolytes. All the resulted solid polymer electrolytes were characterized using electrochemical impedance spectroscopy (EIS), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) methods. In the present study, the XRD, FTIR, SEM, and DSC results show clear evidence of the miscibility of PMMA and PEO. The incorporation of PMMA into the PMMA–PEO-blend solid polymer electrolytes shows significant improvement on ionic conductivity when small amount of PMMA is used. The highest ionic conductivity of 2.6301 × 10−4 S/cm is achieved for 5 wt% PMMA and 95 wt% PEO-blend solid polymer electrolytes at room temperature. The ionic conductivity values are found to be decreased when a higher wt% of PMMA is added. Upon incorporation of 20 wt% of PMMA, the ionic conductivity values are found in range of 10−6 to 10−7 S/cm. This finding is comparable with the reported results for gel-type polymer electrolytes. Hence, the amount of PMMA used in the PMMA–PEO-blend systems is crucial in the preparation of PMMA–PEO-blend solid polymer electrolyte.

Interstellar communication: The colors of optical SETI

It has recently been argued from a laser engineering point of view that there are only a few magic colors for optical SETI. These are primarily the Nd:YAG line at 1064 nm and its second harmonic 532.1 nm. Next best choices would be the sum frequency and/or second harmonic generation of Nd:YAG and Nd:YLF laser lines, 393.8 nm (near Fraunhofer CaK), 656.5 nm (H$\alpha$) and 589.1 nm (NaD2). In this paper, we examine the interstellar extinction, atmospheric transparency and scintillation, as well as noise conditions for these laser lines. For strong signals, we find that optical wavelengths are optimal for distances $d\lesssim\,$kpc. Nd:YAG at $\lambda=1{,}064\,$nm is a similarly good choice, within a factor of two, under most conditions and out to $d\lesssim3\,$kpc. For weaker transmitters, where the signal-to-noise ratio with respect to the blended host star is relevant, the optimal wavelength depends on the background source, such as the stellar type. Fraunhofer spectral lines, while providing lower stellar background noise, are irrelevant in most use cases, as they are overpowered by other factors. Laser-pushed spaceflight concepts, such as "Breakthrough Starshot", would produce brighter and tighter beams than ever assumed for OSETI. Such beamers would appear as naked eye stars out to kpc distances. If laser physics has already matured and converged on the most efficient technology, the laser line of choice for a given scenario (e.g., Nd:YAG for strong signals) can be observed with a narrow filter to dramatically reduce background noise, allowing for large field-of-view observations in fast surveys.

Thermally Activated Delayed Fluorescence Host for High Performance Organic Light-Emitting Diodes

Thermally activated delayed florescence (TADF) materials can be an efficient host in organic LED (OLED). It is because it is possible to couple energetically the emission energy level of a dopant to the energy levels in the TADF material. In this work fluorescent emitters 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5 H,11H-10-(2-benzothiazolyl)quinolizino-9,9a,1gh coumarin (c545t) and 5,6,11,12-tetraphenyltetracene (rubrene) were used as dopants in a blended TADF host; tris(4-carbazoyl-9-ylphenyl)amine (TCTA) with 2,4,6-tris(3′-(pyridin-3-yl)biphenyl-3-yl)-1,3,5-triazine (Tm3PyBPZ). The blended TADF host has an energy difference between the singlet and triplet excited states (ΔEST) around 27 meV with the yield of reverse intersystem crossing (ФRISC) nearly 100%. This high ФRISC yield enhances the OLED performance with the c545t doped OLED having 11.9% external quantum efficiency and 10% for the rubrene doped OLED.

Investigation of ionic conduction in PEO–PVDF based blend polymer electrolytes

We investigate the effect of blend host polymer on solid polymer electrolyte (SPE) films doped with ammonium iodide (NH4I) salt using a variety of experimental techniques. Structural studies on the composite SPEs show that the blending of Poly(ethylene oxide) (PEO)–Poly(vinylidene fluoride) (PVDF) polymers in a suitable ratio enhances the amorphous fraction of the polymer matrix and facilitates fast ion conduction through it. We observe that the addition of a small amount of PVDF in the PEO host polymer enhances the ion – polymer interaction leading to more ion dissociation. As a result, the effective number of mobile charge carriers within the polymer matrix increases. Systematic investigation in these blend SPEs shows that the maximum conductivity (1.01 × 10–3 S/cm) is obtained for PEO – rich (80 wt. % PEO, 20 wt. % PVDF) composites at 35 wt. % NH4I concentration at room temperature. Interestingly, at higher salt concentrations (above 35 wt. %), the conductivity is found to decrease in this system. The reduction of conductivity at higher salt concentrations is the consequence of decrease in the carrier concentration due to the formation of an ion pair and ion aggregates. PVDF–rich compositions (20 wt. % PEO and 80 wt. % PVDF), on the other hand, show a very complex porous microstructure. We also observe a much lower ionic conductivity (maximum ∼ 10–6 S/cm at 15 wt. % salt) in these composite systems relative to PEO-rich composites.

Fabrication of polymer blend composites based on [PVA-PVP](1−x):(Ag2S)x (0.01 ≤ x ≤ 0.03) with small optical band gaps: Structural and optical properties

In this paper composite materials, based on polymer blends of polyvinyl alcohol (PVA): polyvinyl pyrrolidone (PVP) with small optical band gap, has been studied. Silver sulfide (Ag2S) semiconductor particles have been synthesized in PVA:PVP blend host polymer, using in situ method. X-ray diffraction (XRD) analyses and Fourier transform infrared (FTIR) spectroscopy for the composite samples were carried out. From the XRD pattern, distinguishable crystalline peaks caused by the Ag2S semiconductor particles were observed. From the result of FTIR spectroscopy, the intensity of the FTIR bands were shifted and increased, revealing the occurrence of interactions between the PVA:PVP blend system and Ag2S particles. The composite samples were found to exhibit absorption spectra that cover UV–visible to near infrared regions. The absorption edge was found to be 5eV for pure PVA:PVP system and shifted to 1.15eV for incorporated PVA:PVP with 3M of Ag2S. The refractive index was also evaluated for the samples and observed to be increased from 1.15 to 1.52 as doping increased to the highest. A linear relationship between the refractive index and the filler fraction has been reported. Theoretical discussion of optical dielectric loss, which is a crucial parameter for the band gap estimation, was given. The achieved results reveal that spectra of the optical dielectric loss (ɛi) can be used to study the band gap structure and Tauc's model can be important in determining the types of electronic transition. The optical band gap was found to decrease from 5.2eV for the pure PVA:PVP to 1.1eV for doped PVA:PVP with 3M of Ag2S. Such reduction can be associated with the increase of optical dielectric constant. Finally, the correlation between optical dielectric constant and density of states was discussed.