Organic light emitting diodes: Energy saving lighting technology—A review

This paper reflects the achievements and the challenges ahead in the field of organic light emitting diodes (OLEDs). The primary intention of this paper is to study different organic materials synthesized so far and the OLEDs fabricated for solid-state lighting. After deep review of literature we have synthesized and characterized rare earth based europium organic complexes Eu(TTA)₃Phen, Eu_(x)Y_(1?x)(TTA)₃Phen, and Eu_(x)Tb_(1?x)(TTA)₃Phen, where x = 0.4 and 0.5 by solution technique maintaining stoichiometric ratio. Blended films of pure and doped Eu complexes that are molecularly doped into polymer resins namely polymethylmethacrylate (PMMA) and polystyrene (PS) are prepared according to weight percentage. Concentration effect on absorption and emission spectra of the blended films was studied for different weight percentages (10, 25, 50, 60%). All the complexes doped in PMMA showed an excellent transparency of 90–97% while the complexes doped in polystyrene showed a transparency of 85–90%, bit less than in PMMA. Energy gap of the synthesized complexes have been determined in PMMA and PS. Considering the facts that these complexes have good solubility in most of the organic solvents, the absorption spectra of Eu(TTA)₃Phen, Eu_0.5Y_0.5(TTA)₃Phen and Eu_0.5Tb_0.5(TTA)₃Phen complexes are studied, and OLED devices having the structure ITO/m-MTDATA/α-NPD/TPBi:Eu_(x)Y_(1?x)(TTA)₃Phen/Alq₃/LiF:Al (where x = 0.4, 0.5) were fabricated and characterized. Significant red emission was observed from fabricated OLED devices at 612 nm when operated in a range of 10–18 V. Thus the synthesized rare earth based organic complexes are the best suitable candidates for fabrication of red OLED devices. The extensive review on OLEDS concludes that our present lighting system can be replaced with white OLEDS, recently developed energy saving lighting technology.     

Magnetic binary oxide particles (MBOP): a promising adsorbent for removal of As (III) in water

Magnetic binary oxide particles (MBOP) synthesized using chitosan template has been investigated for uptake capacity of arsenic (III). Batch experiments were performed to determine the rate of adsorption and equilibrium isotherm and also effect of various rate limiting factors including adsorbent dose, pH, optimum contact time, initial adsorbate concentration and influence of presence cations and anions. It was observed that uptake of arsenic (III) was independent of pH of the solution. Maximum adsorption of arsenic (III) was ∼99% at pH 7.0 with dose of adsorbent 1 g/L and initial As (III) concentration of 1.0 mg/L at optimal contact time of 14 h. The adsorption equilibrium data fitted well to Langmuir and Freundlich isotherm. The maximum adsorption capacity of adsorbent was 16.94 mg/g. With increase in concentration of Ca²⁺, Mg²⁺ from 50 mg/L to 600 mg/L, adsorption of As (III) was significantly reduced while for Fe³⁺ the adsorption of arsenic (III) was increased with increase in concentration. Temperature study was carried out at 293 K, 303 K and 313 K reveals that the adsorption process is exothermic nature. A distinct advantage of this adsorbent is that adsorbent can readily be isolated from sample solutions by application of an external magnetic field. Saturation magnetization is a key factor for successful magnetic separation was observed to be 18.78 emu/g which is sufficient for separation by conventional magnate.     

Microneedles for transdermal drug delivery: a systematic review

Transdermal route has been explored for various agents due to its advantage of bypassing the first pass effect and sustained release of drug. Due to strong barrier properties of the skin, mainly stratum corneum (SC), the delivery of many therapeutic agents across the skin has become challenging. Few drugs with specific physicochemical properties (molecular weight <500?Da, adequate lipophilicity, and low melting point) can be effectively administered via transdermal route. However, delivery of hydrophilic drugs and macromolecular agents including peptides, DNA and small interfering RNA is challenging. Drug penetration through the SC may involve bypass or reversible disruption of SC layer by various means. Recently, the use of micron-scale needles has been proposed in increasing skin permeability and shown to dramatically increase permeation, especially for macromolecules. Microneedles (MNs) can penetrate through the SC layer of the skin into the viable epidermis, avoiding contact with nerve fibers and blood vessels that reside primarily in the dermal layer. This review summarizes the types of MNs and fabrication techniques of different types of MNs. The safety aspects of the materials used for fabrication have been discussed in detail. Biological applications and relevant phase III clinical trials are also highlighted.     

Synthesis,structural, photoluminescence and mechanoluminescence properties of Tb<Superscript>3+</Superscript>: Ca<Subscript>2</Subscript>Gd<Subscript>2</Subscript>W<Subscript>3</Subscript>O<Subscript>14</Subscript> novel green nanophosphors

Novel green nanophosphors Ca₂Gd₂W₃O₁₄: Tb³⁺ were synthesized by solid state reaction method. From the X-ray diffraction profiles it is observed that Tb³⁺: Ca₂Gd₂W₃O₁₄ phosphors were crystallized in the form of tetragonal structure. The scanning electron microscopy (SEM) image shows that the particle size is at around 300 nm. In addition to these the prepared powder phosphors were also examined by the energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and mechanoluminescence (ML) spectra. Emission spectra of Tb³⁺: Ca₂Gd₂W₃O₁₄ nanophosphors have shown bright green emission at 545 nm (⁵D₄ → ⁷F₅) with an excitation wavelength λ_exci = 374 nm (⁷F₆ → ⁵G₆). ML spectra shows the radiation effect on the Ca₂Gd₂W₃O₁₄: Tb³⁺ nanophosphors and from that it was observed that these phosphors are very less sensitive for lower exposure.     

Thermoluminescence properties of γ-irradiated KCaSO<Subscript>4</Subscript>Cl: X (X = Ce,Dy, Mn or Pb)

A new phosphor KCaSO₄Cl is very interesting for thermoluminescent properties. In this article, we present results concerning the main dosimetric properties of KCaSO₄Cl activated by Ce, Dy, Mn, and Pb at various concentrations. Polycrystalline KCaSO₄Cl: (Ce; Dy; Ce, Dy; Mn; Ce, Mn; Pb and Ce, Pb) phosphors prepared by solid state diffusion method have been studied for its thermoluminescence (TL) characteristics. The TL glow curves of γ-irradiated all KCaSO₄Cl samples show strong single glow peaks indicating that only one type of trap can be formed. The intensity of the TL glow peaks increases with increase of the γ-ray dose to the samples but the intensity of the TL glow peaks increases with decrease of the concentration of the dopent. The sensitivity of all the phosphors presented here are more than that of CaSO₄: Dy. The phosphors have a simple TL glow curve structure with a prominent peak at the lower temperature side. TL response, fading, reusability of the phosphors are also studied, and it is found that the phosphor is quite suitable for use in dosimetry of ionizing radiations.     

Effect of Synthesis Method on Photoluminescence Properties of Na2Sr2Al2PO4Cl9:Ce3+ Nanophosphor

Nano-Micro Letters - We have synthesized a series of single-composition emission Na2Sr2Al2PO4Cl9:Ce3+ phosphor by traditional solid state reactions and novel combustion method. Formation of...     

A review on pectinase properties,application in juice clarification,and membranes as immobilization support

Pectic substances cause haziness and high viscosity of fruit juices. Pectinase enzymes are biological compounds that degrade pectic compounds. Nontoxicity and ecofriendly nature make pectinases excellent biocatalysts for juice clarification. However, the poor stability and nonreusability of pectinases trim down the effectiveness of the operation. The immobilization techniques have gained the attention of researchers as it augments the properties of the enzymes. Literature has reported the stability improvement of enzymes like lipase, laccase, hydrogen peroxidase, and cellulase upon immobilization on the membrane. However, only a few research articles divulge pectinase immobilization using a membrane. The catalysis-separation synergy of membrane-reactor has put indelible imprints in industrial applications. Immobilization of pectinase on the membrane can enhance its performance in juice processing. This review delineates the importance of physicochemical and kinematic properties of pectinases relating to the juice processing parameters. It also includes the influence of metal-ion cofactors on enzymes’ activity. Considering the support and catalytic-separation facets of the membrane, the prediction of the membrane as support for pectinase immobilization has also been carried out.     

Combustion synthesis of Ce~（3＋）, Eu~（3＋） and Dy~（3＋） activated NaCaPO_4 phosphors

The preparation of NaCaPO4 doped with rare earth (RE) ions Ce3+, Eu3+ and Dy3+ by combustion method was described. Under UV excitation (251 nm) of NaCaPO4:Ce3+ showsd emission (367 nm) in UV range. When NaCaPO4:Dy3+ phosphor was excited at 349 nm, the emission spectrum showed intense bands at 482 nm (blue) and 576 nm (yellow). In Eu activated NaCaPO4 phosphor, the emission spectrum showed a dominant peak at 594 nm (orange) while others were at 614 and 621 nm (red) when excited at 393 nm. The prepared phosph...     

Efficient Red Downshifting in Layered Structure: A Broad Spectral Converter for Enhancing Photo-response of Solar Cell

Spectral convertors are promising materials for solar cells as they engineered the band gap necessary for suppressing the losses. Existing spectral convertors have small stokes shift which exerts re-absorption losses due to the overlap of spectrum and limits light catching ability. Here we present large stoke shift chromium doped rhombohedral Al₂O₃: Cr³⁺ as a spectral convertor from UV–VIS to red region as single doped with maximum coverage of solar spectrum in UV region. The large stoke shifts in red region around 694 nm originate from ²E_g to ⁴A_2g and broad absorption originates from \(^{{\text{4}}}{{\text{A}}_{{\text{2g}}}}{ \to ^{\text{4}}}{{\text{T}}_{{\text{1g}}}},{{\text{ }}^{\text{4}}}{{\text{A}}_{{\text{2g}}}}{ \to ^{\text{4}}}{{\text{T}}_{{\text{2g}}}}\). This broad absorption (300–600 nm) and large stokes shift emission at 694 nm suggest that the Cr³⁺ dopant rhombohedral Al₂O₃ is well suited as spectral convertors for enhancing the efficiency of the solar cell through better matching of spectral response with spectral distribution of light striking on the solar cell.