Visible Region Of Light Spectrum Research Articles

Synthesis of rare-earth nanosized phosphors using microwave processing

Nanomaterials find permanently extending applications in various areas of life. In particular, nanosized phosphors can be used as pharmaceutical carriers capable of emitting ultraviolet or visible light that activates a photosensitizer, thus significantly expanding the possibilities of photodynamic therapy in the treatment of oncological, bacterial and viral diseases. The conditions required for the use of nanosized phosphors in medicine include their fine dispersion and effective luminescence in the red region of visible light spectrum upon stimulation by X-ray radiation of the range accepted for medical applications, particularly for diagnostic and therapeutic purposes in many diseases. The aim of this work was to study the effect of microwave treatment of Y2O3:Eu phosphors prepared by hydrothermal synthesis in ethylene glycol at 230 °C for 6 hours, involving the decomposition of mixed acetate. In order to reduce the aggregation and growth of the resulting particles, Aerosil A300 with average particle size 7 nm was added to the reaction mixture in the course of hydrothermal synthesis in the ratio 1:1 relating to the obtained phosphor. The microwave treatment was carried out at 800 °C for 5 minutes. The developed method provided Y2O3:Eu phosphor samples featuring with increased luminescence intensity in the region 610…700 nm compared to similar phosphors earlier prepared using the rapid thermal annealing (RTA) procedure.

Synthesis and visible-light photocatalytic potential of nanocomposite based on the cadmium sulfide and titanoniobate

Nanocomposite CdS/HTiNbO5 photocatalysts with application in the visible-light region of spectrum were synthesized via modified precipitation method using HTiNbO5 nanosheet as a subject material and CdS as an object material. The phase identification, morphologies and composites of the as-prepared photocatalysts were characterized by X-ray diffraction, Laser Raman spectra, High resolution transmission electron microscopy and X-ray photoelectron spectroscopy and another. Both photocatalytic activity and stability of the photocatalysts were evaluated by degradation of methylene blue under visible light irradiation. These nanocomposite photocatalysts exhibit a higher activity than single-phase photocatalysts. The optimal CdS/HTiNbO5 nanocomposite shows the highest degradation rate of 0.024 min−1 with 10 wt% CdS content, which is about 8.9 and 7.3 times that of pure HTiNbO5 nanosheet and CdS, respectively. A possible mechanism for enhanced photocatalytic activity is discussed.

Novel blue-light emitting fluorescent liquid crystals based on 4, 4′-(2-(tert-butyl)- anthracene-9, 10-diyl)diphenol and their optical behavior

Novel fluorescent liquid crystals based on 4, 4′-(2-(tert-butyl)-anthracene-9, 10-diyl)diphenol moiety were synthesized in good yields and were found to be enantiotropic liquid crystals. Their excitation wavelength was found to be at 265 nm and emission maximum was observed at λmax = 435 nm, which corresponds to the blue region of visible light spectrum. The values of refractive indices, recorded at variable temperatures and wavelengths showed a sudden decline in temperature range in which mesophases were observed. Interaction with DNA, as evaluated by UV–Visible and Fluorescence spectroscopy showed the formation of a complex of compound-hsDNA, mainly through minor grooves.

Synthesis and characterization of copper antimony tin sulphide thin films for solar cell applications

Low price thin film modules based on Copper antimony tin sulphide (CATS) are introduced for solar harvesting to compete for the already developed compound semiconductors. Here, CATS thin films were deposited on soda lime glass by thermal evaporation technique followed by a rapid thermal annealing in an argon atmosphere. From Our XRD analysis, it was revealed that the annealed samples were poly-crystalline and their crystallinity was improved with increasing annealing temperature. The constituent elements and their corresponding chemical states were identified using X-ray photoelectron spectroscopy. The obtained optical band gap of 1.4eV for CATS thin film is found nearly equal to GaAs – one of the highly efficient thin film material for solar cell technology. Furthermore, our observed good optical absorbance and low transmittance for the annealed CATS thin films in the visible region of light spectrum assured the aptness of the CATS thin films for solar cell applications.

Effect of Dye on the Performance of Nitrogen Doped TiO2 Solar Cell Prepared via Ammonia Treated Liquid Phase Deposition Technique

This paper reports the utilization of nitrogen-doped TiO2 nanoparticle in dye-sensitized solar cell (DSSC). The TiO2 nanoparticles were synthesized on ITO substrate via a simple technique, namely, liquid phase deposition (LPD). 7.5% nitrogen from NH3 dopant source was doped into the TiO2 samples by spin coating technique. The nitrogen doped TiO2 samples were then utilized as photovoltaic materials in a photoelectrochemical cell of ITO/TiO2/electrolyte/platinum sensitized with N-719, N-3 and Z-907 dyes, respectively. It was found that the photovoltaic parameters such as short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF) and power conversion efficiency (η) are influenced by the organic dyes. The cell sensitized with N-719 dye demonstrated the highest photovoltaic parameters. These results are supported with the UV-Vis analysis, showing that the N-719 dye possessed the broadest window absorption and the highest absorption peak in visible region of light spectrum.

Specific Chromophore-Protein Interactions in Bacteriophytochromes Rpbphp2 and Rpbphp3 from Rhodopseudomonas Palustris

Various organisms can sense light through a large family of signaling proteins known as photoreceptors. Upon absorption of a photon in the appropriate wavelength range, photoreceptors undergo structural changes in the chromophore, an organic pigment embedded in the photosensory module of the protein. Phytochromes are red-light photoreceptors originally discovered in plants and more recently in bacteria. They are unique in their ability to undergo reversible photoconversion between two photoisomerizable states, Pr (red light ∼ 700 nm) and Pfr (far-red light ∼ 750 nm). In the photosynthetic bacterium, Rhodopseudomonas palustris, a pair of bacteriophytochromes, RpBphP2 (P2) and RpBphP3 (P3) modulate synthesis of a light-harvesting complex. P2 and P3 have the same biliverdin chromophore (BV) and share 52% amino acid sequence identity, yet they have distinct photoconversion properties. P2, similar to classical bacteriophytochromes, alternates between Pr and Pfr states. P3 is unusual since it alternates between Pr and a unique Pnr (near-red light ∼ 650 nm) state. Our experimental goal is to identify amino acid residues that form specific interactions with BV during photoconversion and as such play key roles in forming distinct photoisomerizable states of P2 and P3. Through site-directed mutagenesis of conserved amino acids informed by structural and sequence analysis of bacteriophytochromes, we created a single-amino acid mutant variant of P3 T480P that undergoes classic reversible photoconversion between Pr and Pfr states. We also report on P2 and P3 mutants that show minimal absorption in the red region of visible light spectrum or are naturally more fluorescent than wild-type proteins. Currently, we are investigating chemical mechanisms that justify observed P2 and P3 mutant phenotypes.