Effect of capping agent on the particle size of CdSe nanoparticles

CdSe nanoparticles were synthesized by green route and chemical route methods. In the green route method the samples were capped by starch and in the chemical route method the samples were capped by mercaptoacetic acid (MAA). The samples were characterized by powder X‐ ray diffraction (XRD) and transmission electron microscopy (TEM). Both the samples showed zinc blend structure. The optical absorption spectra and Fourier transform infrared (FTIR) spectra were also studied. A blue shift was seen in the absorption spectra as compared with the bulk as well as the sample capped by starch. TEM images showed agglomeration for the starch‐capped sample as compared with the MAA‐capped sample. The particle size for the sample capped by MAA was found to be less as compared with the starch‐capped sample. A blue shift in the photoluminescence (PL) spectra was also recorded for the samples prepared by the chemical route as compared with the sample prepared by the green route as well as the bulk. The PL peak shifted towards the red side and increase in the peak intensity occurred with the change in the excitation wavelength. Change in PL intensity was observed with different pH at 685 nm. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of synthesis method and chemical reagents on the structural parameters,particle size,and optical and photoluminescence properties of ZnS nanostructures

In this experimental study, ZnS nanostructures were synthesized using two hydrothermal and co‐precipitation methods with different precursors. Different reagents and precursors were changed to obtain the best product size and morphology. The structure and crystal phase of the products were studied using X‐ray diffraction (XRD) patterns. Some structural parameters were calculated using the XRD results and a product composition was obtained by energy dispersive X‐ray (EDX) analysis and Fourier transform infrared (FT‐IR) spectra to study the chemical composition. The size and morphology of ZnS nanostructures were obtained by scanning electron microscopy (SEM). The optical properties of the synthesized ZnS nanostructures were examined using ultraviolet–visible (UV–Vis) spectra to estimate the optical band gap. Band gap energies were higher than those in the ZnS bulk sample, mainly due to quantum size effects. The photoluminescence (PL) properties of the products were investigated using PL spectra. The results showed the effect of two factors, namely synthesis method and chemical reagents, on the structure parameters, crystallite size, product size and morphology, and optical and PL properties.     

Synthesis and photoluminescence study of di‐dendron dendrimers derived from mono‐Boc‐protected ethylenediamine cores

This work is focused on the synthesis and optical properties of cone‐shaped structural feature di‐dendron polyamidoamine dendrimers up to the third generation with mono‐Boc‐protected ethylenediamine (EDA) as a core. Strong UV absorbance spectra and fluorescence spectra from di‐dendron dendrimers with different terminal groups (‐NH₂, ‐COOCH₃) were studied under different conditions by varying experimental parameters such as concentration and pH. The optical density and fluorescence intensities increased when di‐dendron dendrimers generation number increased from 0.5 to 3.0. It was confirmed that the concentration of di‐dendron dendrimers plays an important role in fluorescence intensity. The increase in fluorescence intensity was linear in low concentration regions, but the intensity increased slowly in high concentration regions. The results also showed a rapid increase in fluorescence intensity at low pH. The formation of a fluorescence‐emitting moiety had a close relationship to protonated tertiary amine groups in di‐dendron dendrimers derived from mono‐Boc‐protected EDA cores. Furthermore, the formation of fluorescent chemical species was irreversible. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and characterization of Y(1‐x)Eu(x)(TTA)3(Phen) organic luminescent thin films

Yttrium is stoichiometrically doped into europium by mole percentage, during the synthesis of Y_(1‐x)Eu_(x)(TTA)₃(Phen), using solution techniques (where x = 0.2, 0.4, 0.5, 0.6 and 0.8, TTA = thenoyltrifluoroacetone and Phen = 1,10‐phenanthroline).These complexes were characterized using different techniques such as X‐ray diffraction, thermogravimetric/differential thermal analysis, optical absorption and emission spectra. Thin films of the doped Eu–Y complexes were prepared on a glass substrate under a high vacuum of 10^‐6 Torr. The photoluminescence spectra of these thin films were recorded by exciting the sample at a wavelength of 360 nm. The emission peak for all the synthesized complexes centered at 611 nm; maximum emission intensity was obtained from Y_0.6Eu_0.4 (TTA)₃(Phen). The results proved that these doped complexes are more economical than pure Eu(TTA)₃(Phen) and are best suited as red emissive material for energy‐efficient and eco‐friendly organic light‐emitting diodes and displays. Copyright © 2013 John Wiley & Sons, Ltd.     

Conformation change of hornet silk proteins in the solid phase in response to external stimulation

Hornet silks adopt a variety of morphology such as fibers, sponge, films, and gels depending on the preparation methods. We have studied the conformation change of hornet silk proteins (Vespa mandarina) as regenerated films, using chiroptical spectrophotometer universal chiroptical spectrophotometer 1, which can measure true circular dichroism spectra without artifact signals that are intrinsic to solid‐state samples. The spectra showed that the proteins in films alter the conformation rapidly from the α‐helix to the coiled coil and then to a β‐sheet structure in response to heat/moisture treatment, but the transformation stopped at the coiled coil state when the sample was soaked in EtOH/water solution. Water is required for the α‐helix to the coiled coil transition, and extra energy is required for the further transition to a β‐sheet structure. This is the first successful circular dichroism study of fibril silk proteins to follow the conformation changes in the solid state. This work shows that proteins can undergo conformational changes easily even in the solid phase in response to external stimuli, and this can be traced by solid‐phase‐feasible chiroptical spectrophotometers. Application of unnatural stress to proteins gives valuable insights into their structure and characteristics.     

Nanocrystalline SrS:Ce3+ system for the generation of white light‐emitting diodes

Nanocrystalline SrS phosphors doped with Ce³⁺ ions at different concentrations (0.5, 1, 1.5 and 2 mol%) are synthesized via the solid‐state diffusion method (SSDM), which is suitable for the large‐scale production of phosphors in industrial applications. The as‐prepared samples are characterized using an X‐ray diffraction (XRD) technique, field emission scanning electron microscopy (FESEM), high‐resolution transmission electron microscopy (HRTEM) and energy‐dispersive X‐ray (EDX) analysis. The optical properties of these phosphors are analyzed using reflectance spectra, photoluminescence spectra and afterglow decay curves. The cubic structure of the SrS phosphor is confirmed by XRD analysis and the crystallite size calculated by Scherer's formula using XRD data shows the nanocrystalline nature of the phosphors. No phase change is observed with increasing concentrations of Ce³⁺ ions. The surface morphology of the prepared phosphors is determined by FESEM, which shows a sphere‐like structure and good connectivity of the grains. The authenticity of the formation of nanocrystalline phosphors is examined by HRTEM analysis. Elemental compositional information for the prepared phosphors is gathered by EDX analysis. Photoluminescence studies reveal that the emission spectra of the prepared phosphor shows broad band emission centered at 458 and 550 nm due to the transition of electrons from the 5d → 4f energy levels. The afterglow decay characteristics of different as‐synthesized SrS:Ce³⁺ nanophosphors are conceptually described. Copyright © 2016 John Wiley & Sons, Ltd.     

Luminescence studies of a Li2Ca1−xSiO4:xSm3+ phosphor for the generation of white light under NUV-excited phosphor converting LEDs

In this paper, we present new aspects of Sm³⁺-doped pure Li₂CaSiO₄ as a suitable candidate for white light emitting diode (WLED) applications. The samples were mainly prepared using a conventional modified solid-state synthesis technique. The structural studies were done using X-ray diffraction and Rietveld refinement. Instruments such as a scanning electron microscope (SEM) were used to obtain information about the morphology of the as-prepared samples. Photoluminescence (PL) analysis of phosphor samples for variable concentrations of doping ions with variable excitations were presented. When doped with Sm³⁺ in host Li₂CaSiO₄ it emitted intense blue, green and red emissions and a more intense red emission peak (605 nm) under 408 nm excitation (near-UV–blue). Our study shows that the as-prepared phosphor may be useful for optical devices and mainly for WLEDs. The corresponding transitions of doping ions and concentration quenching effect were studied in detail. The 1931 Commission Internationale de l'Eclairage (x, y) chromaticity coordinates showed the distribution of spectral regions calculated from PL emission spectra and this was found (0.63, 0.36) in the red region, so the phosphor may be useful for near-UV–blue excited WLED applications.     

Influence of synthesis parameters on the optical and photocatalytic properties of solvo/hydrothermal CuS and ZnS nanoparticles

Copper sulfide and zinc sulfide nanostructures were synthesized using a solvo/hydrothermal method and a thio Schiff base ligand, N‐benzylidene ethanethioamide, as a source of sulfide ions. The effects of different synthesis parameters including the type of solvent, temperature, and duration of reactions on the morphology of the CuS and ZnS products were investigated using field emission scanning microscopy and transmission electron microscopy, respectively. The structural aspects of the samples were characterized using powder X‐ray diffraction, Fourier transform infrared spectroscopy, and energy dispersive X‐ray analysis. The optical properties of the samples were studied through their optical absorption and photoluminescence spectra. The photocatalytic ability of the as‐synthesized sulfides was explored by studying the colour removal of methylene blue under ultraviolet light irradiation.     

UV light‐tunable fluorescent inks and polymer hydrogel films based on carbon nanodots and lanthanide for enhancing anti‐counterfeiting

Novel water‐soluble green fluorescent carbon nanodots (CNs) using methacrylic acid and m‐phenylenediamine as precursors were first synthesized using a one‐pot hydrothermal method. Red fluorescent lanthanide complexes were prepared using lanthanide ion Eu³⁺ and pyridine‐2,6‐dicarboxylic acid. The optical properties of CNs were characterized using ultraviolet visible (UV) spectra and fluorescence spectra, microscopic morphology was characterized using transmission electron microscopy (TEM) and dynamic light scattering (DLS), and the elemental composition was characterized using Fourier transform‐infrared spectroscopy (FT‐IR) and X‐ray photoelectron spectra (XPS). The fluorescence spectra of the lanthanide complexes were also measured. A simple strategy was developed to prepare UV light‐tunable fluorescent inks and polymer hydrogels films based on CNs and lanthanide complexes. The fluorescent inks and polymer hydrogels films could be repeatedly switched between green and red fluorescence. The change of color depended on luminescence of the CNs and the lanthanide complexes under 254 and 365 nm UV light, respectively. The UV light‐tunable fluorescent inks and polymer hydrogels films could enhance its anti‐counterfeiting function for data and information.     

Graphite oxide‐dispersed CdTe quantum dots nanocomposite for flexible display luminescent membranes

A quantum dot (QD) dispersant material was prepared using graphite oxide (GO). Luminescent films were prepared using polyvinyl alcohol as the polymer matrix. First, water‐soluble CdTe QDs were prepared by wet chemistry and GO was synthesized using a modified Hummers method. X‐Ray diffraction tests showed that the GO reflection peak [001] was 11.9°, which indicates that the d‐spacing is 0.7431 nm; atomic force microscopy showed a GO thickness of 200 nm. Fourier transform infrared spectra showed vibrations at 1624 cm^?1 for the carbonyl groups, and 3260 cm^?1 for the GO samples; the ‐C–O vibration was at 1320 cm^?1 and ‐COOH, ?OH vibrations were at 950 cm^?1. Fluorescent tests showed that pH had an impact on the QD colloidal stability. GO was neutralized before use as the host media for the GO/QDs nanocomposite. The results proved that the resultant nanocomposite is promising for use in brightness enhancement films in flexible displays.     

Evaluation of trapping parameters of γ‐rays irradiated Dy3+‐doped LaPO4 phosphors

Thermoluminescence (TL) materials are widely used in radiation measurements. The best‐known applications of TL materials are in the dosimetry of ionizing radiation, and in CTV screen phosphors, scintillators, X‐ray laser materials, etc. The TL glow curve and its kinetic parameters for annealed LaPO₄ at different constant temperatures and for Dy³⁺‐doped LaPO₄ phosphors irradiated by gamma‐rays are reported here. The samples were irradiated using a ⁶⁰Co gamma‐ray source at a dose of 10 Gy and the heating rate used for TL measurements was 5ºC/s. The samples were characterized using X‐ray diffraction (XRD), Fourier transform infrared, transmission electron microscopy and TL techniques. The XRD pattern shows that the prepared phosphor has a good crystalline structure with an average crystallite size of ~ 18 nm. The samples show good TL peaks for 0.05, 0.1 and 0.2 mole % doping concentrations of Dy³⁺ ions and anneal above 400ºC. The TL glow curve characteristics of annealed LaPO₄ and Dy³⁺‐doped LaPO₄ were analyzed and trapping parameters calculated using various methods. All TL glow curves obey the second‐order kinetics with a single glow peak, which reveals that only one set of trapping parameter is set for a particular temperature. The TL sensitivity was found to depend upon the annealing temperature and Dy³⁺ doping concentration. The prepared sample may be a new nano phosphor and be useful in TL dosimetry. Copyright © 2014 John Wiley & Sons, Ltd.     

Vibrational circular dichroism of carbohydrate films formed from aqueous solutions

Vibrational circular dichroism (VCD) spectra in the entire 2000-900 cm(-1) region have been recorded, for the first time, for films of carbohydrates prepared from aqueous solutions. Eight different carbohydrates, alpha-D-glucopyranosyl-(1-->4)-D-glucose, cyclomaltohexaose, alpha-D-glucopyranosyl alpha-D-glucopyranoside, beta-D-glucopyranosyl-(1-->6)-D-glucose, beta-D-glucopyranosyl-(1-->4)-D-glucose, D-glucose, and both enantiomers of 6-deoxygalactose and of allose, were investigated. The VCD spectra obtained for films are found to be identical to the corresponding spectra obtained for aqueous solutions of carbohydrates. These measurements demonstrate several advantages of significant importance. The strong infrared absorption of water has prevented, in the past, the pursuit for routine applications of VCD in determining the structures of carbohydrates in aqueous solutions. This limitation is not present for film studies because water solvent is removed in the process of preparing the films. Also, strong infrared absorption of water at 1650 cm(-1) requires the use of very short-pathlength (6 microm) cells for measurements on aqueous solutions. This requirement and concomitant inconveniences (such as laborious assembling of a demountable liquid cell or purchasing an expensive variable pathlength liquid cell) have been eliminated for film measurements. The removal of interfering water absorption in film studies resulted in higher light throughput and better signal-to-noise ratios for VCD measurements. Another point of significance is that the amount of carbohydrate sample required for VCD measurements on films is approximately one to two orders of magnitude smaller than that required for corresponding VCD measurements on aqueous solutions. Since carbohydrate samples can now be studied as films, VCD spectroscopy becomes much more broadly applicable for carbohydrates than previously believed. The present work, in combination with other film measurements in our laboratory, indicate that VCD studies on films can be used more generally, providing a convenient and powerful approach for probing structural information for biologically important compounds.     

Luminescence investigation of a cerium‐doped yttrium vanadate phosphor

Cerium (Ce³⁺)‐doped (1, 3, and 7 mol%) yttrium vanadate phosphors were prepared using a co‐precipitation technique. The structural and optical properties of the synthesized samples were studied using X‐ray diffraction (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HR‐TEM), optical absorption, and photoluminescence (PL) spectroscopy techniques. The tetragonal structure and the formation of the nanosized crystallites in the YVO₄:Ce phosphor were confirmed using XRD analysis. HR‐TEM morphology showed rod‐like nanoparticles of different sizes. Optical absorption spectra demonstrated strong absorption bands at 268 and 276 nm. PL spectra showed strong peaks at 546, 574, and 691 nm following excitation at 300 nm. The calculated CIE chromaticity coordinates demonstrated that YVO₄:Ce could be used as a novel phosphor for the development of light‐emitting diode lamps.     

Wing colors based on arrangement of the multilayer structure of wing scales in lycaenid butterflies (Insecta: Lepidoptera)

Male wing colors and wing scale morphology were examined for three species of lycaenid butterflies: Chrysozephyrus ataxus, Favonius cognatus and F. jezoensis. Measurement of spectral reflectance on the wing surface with a spectrophotometer revealed species‐specific reflection spectra, with one or two peaks in the ultraviolet and/or green ranges. Observations of wing scales using an optical microscope revealed that light was reflected from the inter‐ridge regions, where transmission electron microscopy revealed a multilayer structure. Based on the multilayer dimensions obtained, three models were devised and compared to explain the measured reflectance spectrum. The results showed that the best fit is a model in which thicknesses of thin films of the multilayer system are not constant and air spaces between cuticle layers are more or less packed with cuticle spacers. This suggests that the specific wing colors of the species examined are produced by the species‐specific arrangement of the multilayer structure of wing scales.     

Study of trivalent samarium ion embedded lithium‐based borate glass for high‐density optical memory devices

Sm³⁺ ions doped strontium lithium lead borate glasses (SLLB:Sm) were prepared using a conventional melt‐quenching technique. The glasses were analyzed using X‐ray diffractometry and Fourier transform infrared spectroscopy, optical absorption, fluorescence spectral analysis, and fluorescence lifetime decay. The Judd–Ofelt (J–O) parameters and radiative parameters of the SLLB:Sm10 glass (1.0 mol% Sm³⁺ ion‐doped glass) were calculated using J–O theory. From the emission spectra, among all the synthesized glass, SLLB:Sm10 glass had the highest emission intensity for ⁴G_5/2→⁶H_11/2 transition (610 nm). Emission parameters, such as stimulated emission cross‐section and optical gain bandwidth, were calculated. For all concentrations of Sm³⁺ ions, the decay profile showed an exponential nature and decreased when the Sm³⁺ ion concentration was increased due to a concentration quenching effect. This result suggests that the synthesized SLLB:Sm10 glass could be used for application in high‐density optical memory devices.     

Sensitization enhancement of europium in ZnSe/ZnS core/shell quantum dots induced by efficient energy transfer

Eu‐doped ZnSe:/ZnS quantum dots (formed as ZnSe:Eu/ZnS QDs) were successfully synthesized by a two‐step wet chemical method: nucleation doping and epitaxial shell growing. The sensitization characteristics of Eu‐doped ZnSe and ZnSe/ZnS core/shell QD are studied in detail using photoluminescence (PL), PL excitation spectra (PLE) and time‐resolved PL spectroscopy. The emission intensity of Eu ions is enhanced and that of ZnSe QDs is decreased, implying that energy was transferred from the excited ZnSe host materials (the donor) to the doped Eu ions (the acceptor). PLE reveals that the ZnSe QDs act as an antenna for the sensitization of Eu ions through an energy transfer process. The dynamics of ZnSe:Eu/ZnS core/shell quantum dots with different shell thicknesses and doping concentrations are studied via PL spectra and fluorescence lifetime spectra. The maximum phosphorescence efficiency is obtained when the doping concentration of Eu is approximately 6% and the sample showed strong white light under ultraviolet lamp illumination. By surface modification with ZnS shell layer, the intensity of Eu‐related PL emission is increased approximately three times compared with that of pure ZnSe:Eu QDs. The emission intensity and wavelength of ZnSe:Eu/ZnS core/shell quantum dots can be modulated by different shell thickness and doping concentration. The results provide a valuable insight into the doping control for practical applications in laser, light‐emitting diodes and in the field of biotechnology. Copyright © 2014 John Wiley & Sons, Ltd.     

2‐(4‐Ethoxy phenyl)‐4‐phenyl quinoline organic phosphor for solution processed blue organic light‐emitting diodes

This paper reports the synthesis and characterization of 2‐(4‐ethoxyphenyl)‐4‐phenyl quinoline (OEt‐DPQ) organic phosphor using an acid‐catalyzed Friedlander reaction and the preparation of blended thin films by molecularly doping OEt‐DPQ in poly(methyl methacrylate) (PMMA) at different wt%. The molecular structure of the synthesized phosphor was confirmed by Fourier transform infra‐red (FTIR) spectroscopy and nuclear magnetic resonance spectra (NMR). Surface morphology and percent composition of the elements were assessed by scanning electron microscopy (SEM) and energy dispersive analysis of X‐rays (EDAX). The thermal stability and melting point of OEt‐DPQ and thin films were probed by thermo‐gravimetric analysis (TGA)/differential thermal analysis (DTA) and were found to be 80°C and 113.6°C, respectively. UV–visible optical absorption spectra of OEt‐DPQ in the solid state and blended films produced absorption bands in the range 260–340 nm, while photoluminescence (PL) spectra of OEt‐DPQ in the solid state and blended thin films demonstrated blue emission that was registered at 432 nm when excited at 363–369 nm. However, solvated OEt‐DPQ in chloroform, tetrahydrofuran or dichloromethane showed a blue shift of 31–43 nm. Optical absorption and emission parameters such as molar extinction coefficient (ε), energy gap (E_g), transmittance (T), reflectance (R), refractive index (n), oscillator energy (E₀) and oscillator strength (f), quantum yield (φ_f), oscillator energy (E₀), dispersion energy (E_d), Commission Internationale de l'Éclairage (CIE) co‐ordinates and energy yield fluorescence (E_F) were calculated to assess the phosphor's suitability as a blue emissive material for opto‐electronic applications such as organic light‐emitting diodes (OLEDs), flexible displays and solid‐state lighting technology.     

A Facile Thermal-Treatment Route to Synthesize ZnO Nanosheets and Effect of Calcination Temperature

A facile thermal-treatment route was successfully used to synthesize ZnO nanosheets. Morphological, structural, and optical properties of obtained nanoparticles at different calcination temperatures were studied using various techniques. The FTIR, XRD, EDX, SEM and TEM images confirmed the formation of ZnO nanosheets through calcination in the temperature between 500 to 650°C. The SEM images showed a morphological structure of ZnO nanosheets, which inclined to crumble at higher calcination temperatures. The XRD and FTIR spectra revealed that the samples were amorphous at 30°C but transformed into a crystalline structure during calcination process. The average particle size and degree of crystallinity increased with increasing calcination temperature. The estimated average particle sizes from TEM images were about 23 and 38 nm for the lowest and highest calcination temperature i.e. 500 and 650°C, respectively. The optical properties were determined by UV–Vis reflection spectrophotometer and showed a decrease in the band gap with increasing calcination temperature.     

Infrared and visible emissions of rare‐earth‐doped CeO2 phosphor

This paper reports the synthesis and characterization of Er³⁺‐doped CeO₂ phosphor with variable concentrations of erbium. The sample was synthesized using a solid‐state reaction method, which is useful for the large‐scale production of phosphors and is also eco‐friendly. The prepared sample was characterized using an X‐ray diffraction (XRD) technique. The XRD pattern confirmed that sample has the pure cubic fluorite crystal structure of CeO₂. The crystallite size of the prepared phosphor was determined by Scherer's formula and the crystallite size giving an intense XRD peak is 40.06 nm. The surface morphology of the phosphor was determined by field emission gun scanning electron microscopy (FEGSEM). From the FEGSEM image, good surface morphology with some agglomerates was found. The functional group in the prepared sample was analysed by Fourier transform infrared (FTIR) spectroscopy. All samples prepared with variable concentrations of Er³⁺ (0.1–2 mol%) were studied by photoluminescence analysis and it was found that the excitation spectra of the prepared phosphor shows broad excitation centred at 251 nm. Emission spectra at different concentrations of Er³⁺ show strong peaks at 413 and 470 nm and a weaker peak at 594 nm. The dominant peaks at 413 and 470 nm are caused by the allowed electronic transition ⁴S_3/2 → ⁴I_15/2 and the weaker transition at 594 nm is due to the transition ⁴ F_9/2 → ⁴I_15/2. Spectrophotometric determinations of peaks were evaluated using the Commission Internationale de I'Eclairage (CIE) technique. The emission spectra were also observed using an infrared (IR) laser 980 nm source, and three distinct peaks were found in the IR region at 848, 870 and 980 nm. The prepared phosphor has utility for application in display devices. Copyright © 2015 John Wiley & Sons, Ltd.     

Intense visible multicolored luminescence from lanthanide ion‐pair codoped NaGdF4 nanocrystals

Lanthanide ion‐pair (Eu³⁺/Tb³⁺, Dy³⁺/Tb³⁺, Sm³⁺/Tb³⁺ and Eu³⁺/Dy³⁺) codoped NaGdF₄ nanocrystals using Ce³⁺ as the sensitizer were prepared via the polyol method. The nanocrystals with different codoped lanthanide ion‐pairs retain their individual optical properties and the combined spectra can be detected using single‐wavelength excitation at about 251 nm. The combined spectra intensity ratios can be adjusted through control of the doping ions molar ratios. Excited with a UV lamp at 254 nm, the as‐prepared nanocrystals in aqueous solution emit intense visible emissions of different colors. The nanocrystals were coated with SiO₂, to make them biocompatible. Copyright © 2009 John Wiley & Sons, Ltd.