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The melt quenching procedure has been followed to synthesize transparent Tb3+ singly activated and Tb3+/Eu3+ co-activated TeO2–WO3–K2O–ZnO–Bi2O3 (TWKZBi) glasses. The structural characteristics of the prepared TWKZBi glass samples were examined through x-ray diffraction. The existence of functional units corresponding to the different vibrations has been examined via Raman spectroscopy. The photoluminescent characteristics and energy transfer (ET) analysis in the Tb3+/Eu3+ co-activated TWKZBi glasses were investigated in depth. Several emission peaks have been observed in Tb3+ doped TWKZBi glasses under n-UV and blue excitations and the maximum luminescent intensity has been detected for 2.0 mol% of Tb3+ doped TWKZBi glass sample. The emission spectra of co-doped Tb3+ and Eu3+ ions in the TWKZBi glasses have been studied, and the maximum ET efficiency is found to be 32.82% under n-UV excitation. The ET from sensitizer (Tb3+) to activator (Eu3+) ions happen through dipole–dipole interaction, as confirmed by Dexter's and Reisfeld's approximation. The colour-tunable emission in the prepared glass samples can be achieved via varying the content of activator ions. The decay profiles for the 5D4 level of Tb3+ ions diminish with varying the concentration of Eu3+ ions, confirming the ET from Tb3+ to Eu3+ ions. Furthermore, temperature-dependent photoluminescence studies show that the Tb3+/Eu3+ co-doped TWKZBi glasses have good thermal stability. All the aforementioned results reveal the suitability of the Tb3+/Eu3+ co-activated TWKZBi glass samples for photonic applications. [ABSTRACT FROM AUTHOR]

Piezoelectric materials have been widely used for various applications like MEMS and energy harvesting. The PZT (PbZr0. 52Ti0.48O3) is one among of all piezoelectric materials, which exhibit vital role for fabrication of devices. The present manuscript is described about PZT powders, which were synthesized by solgel method and yielded powders were annealed at different temperature to get stabilized structure without any impurities phase with help of X-ray diffraction. As a part of structural investigation, Raman spectroscopy was done over the different temperature annealed powders and identify Raman active modes. The band gap energy was found for these nano powders that are increasing with respect to annealing temperature. The microstructure of nano PZT powders has found with help FESEM, which provided the particles size with order of 50–70 nm diameters. Electrical properties i.e., the P-E loop was done on nano PZT, polarization has increased and leakage current also increased for annealed temperatures. The terahertz spectra of PZT results suggested that the absorption coefficient peak are found at higher frequency, refractive index peak found lower frequency for annealed PZT samples. The 600 oC is shown maximum dielectric constant & refractive index at 0.6 THz, which is confirmed by the electric properties of PZT. As annealing temperature increases, dielectric and refractive index decreased due to depolarization. Highlights: PZT nano powders obtained from Solgel method. Tetragonal structure found from the XRD and accordingly Raman modes assigned. Energy gap of PZT increased with annealing temperature. Electric polarization increased with annealing temperature. Terahertz spectra provides refractive and dielectric constant, which decreased with frequency. [ABSTRACT FROM AUTHOR]

Psoriasis is a noncontagious, long‐lasting skin infection that affects many people around the world. Numerous therapeutic artificial treatments are available for the treatment of psoriasis, such as photodynamic therapy using broadband ultraviolet (UV) lamps, which have harmful effects on human skin. Similarly, the natural healing systems such as sunlight have a higher risk of sunburn and can cause dangerous forms of skin cancer. Significant light emission of a specific wavelength (in the UV range), and phosphor‐based devices demonstrate the effectiveness of treating psoriasis without damaging the skin. Gd3+‐doped calcium magnesium silicate [Ca2MgSi2O7:Gd3+,(CMS:Gd3+)] phosphor is one of the ideal phosphors that emit specific narrow UV wavelengths for curing psoriasis and is in great demand in the field of dermatology. Photoluminescence analysis at room temperature (~25°C) shows that the synthesized CMS:Gd3+ phosphor emits narrowband UV‐B light with a peak intensity at 314 nm. Comparative studies of the standard action spectrum of psoriasis with the emission spectrum of the CMS:Gd3+ phosphor show that the synthesized phosphor was the most suitable material for treating a variety of diseases, including psoriasis, vitiligo, type‐1 diabetes, dental disease, sleep and mood disorders, and other skin diseases. [ABSTRACT FROM AUTHOR]

We have presented varied shaped CdSe nanoparticles (NPs) synthesized by solution-based one-pot hot injection colloidal method by varying the precursor salt of Cd (i.e., cadmium oxide, cadmium chloride, and cadmium acetate) at an optimized Cd/Se ratio (2:1). CdSe nanoparticles of varied shapes and sizes (5–25 nm) were synthesized by using Butylamine and Octadecene as capping ligands and the nucleation and growth mechanism has been explained using LaMer's diagram. It has been found that Butyl amine owing to its improved capping effect and better surface-traps passivation, aids in emission intensity enhancement of CdSe QD's. The optical properties of the as-synthesized CdSe colloidal NPs have been investigated in terms of quantum confinement effects to reveal their suitability as a pursuing material for UV-LED. Variation in the morphology of CdSe NPs synthesized using different precursor sources leads to changes in the bandgap for its potential application in QD-based LEDs. To the best of the author's knowledge, this is the first-hand report on the synthesis of CdSe QD's from varied Cd-precursor sources using butyl amine and octadecene as capping ligands via hot injection technique for UV-LED applications. [ABSTRACT FROM AUTHOR]

The photoluminescent (PL) properties of Sm3+-doped strontium hexaborate (SrB6O10) phosphors are significantly influenced by their crystallinity, phase and dopant concentration. To obtain a high brightness orange-red emitting SrB6O10:Sm3+ phosphor, a controlled and modified soluble-salt reaction method in the presence of a chelating agent (citric acid, C6H8O7) was used at ∼700 °C for about half an hour under an air atmosphere, which is otherwise only possible at very high (>1500 °C) sintering temperatures. The PL spectrum of the SrB6O10:Sm3+ phosphor produced strong and intense PL emission peaks centered at 560 nm (4G5/2 → 6H5/2), 596 nm (4G5/2 → 6H7/2), and 640 nm (4G5/2 → 6H9/2) under excitation of 400 nm (6H5/2→ 6H7/2). This is one of the very few reports that depicts the formation of more shallow traps in the lattice and the concentration quenching phenomenon was attributed to the non-radiative transfer of energy among Sm3+ ions via dipole–dipole interactions in the trap states. The optimized phosphor has noticeable reddish-orange Commission International de I'Eclairage color coordinates of (0.459, 0.337). The PL decay kinetics of the synthesized phosphor showed a biexponential decaying characteristic with an overall decay time of milliseconds. The presence of borate ions benefitted the thermal stability of the SrB6O10:Sm3+ phosphor as well. X-ray diffraction studies confirmed the phase purity, while scanning electron microscopy revealed the morphology to be an agglomerated rod-like structure. The PL intensity increased with increasing Sm3+ concentration and reached the optimum at 0.1 mol%. The obtained results clearly indicate that the SrB6O10:Sm3+ phosphor is a viable material for providing a red component for white-light emitting diodes (w-LEDs). [ABSTRACT FROM AUTHOR]

The alignment of smectic C* liquid crystals (LCs) has been manipulated over and near different surfaces such as bare glass, indium tin oxide (ITO) coated glass, patterned glass, and near spacers. The LC sample cell is made of one ITO coated glass plate and other having striped ITO with a Mylar spacer maintaining a finite cell gap between them. Laser scribing is used to make striped ITO, while the scribed area results in the formation of the patterned glass surface. The geometry of the cell is such that overlapped ITO lie in the middle and spacers are placed in the two extreme corners of the cell. The alignment of LC is found to be homeotropic over the ITO coated glass, while it is planar near the spacer. Interestingly, a transition from homeotropic to planar is observed while moving away from the middle towards either corner of the cell. The origin of both types of alignment in the same cell has been explained by considering the difference in the surface energy of different surfaces. This work renders new advancement towards the manipulation of LC alignment using different surfaces and interfaces for advanced electro-optical and photonic devices based on LCs. [ABSTRACT FROM AUTHOR]

The present work elucidates a systematic exploration of structural, morphological, and photoluminescence (PL) features of sol–gel derived Dy3+ doped sodium calcium silicate (Na2CaSiO4: NCS) phosphor. The X-ray diffraction (XRD) data indicate single-phase cubic crystal formation of NCS: Dy3+ phosphors as all the present diffraction peaks are in accordance with the standard Na2CaSiO4 data (JCPDS card No. 24-1069). The scanning electron microscopy (SEM) image of the as-synthesized NCS sample reveals irregular crystalline structures coalesced together to form micro-sized particles. The PL studies of NUV excited Dy3+ doped NCS phosphors disclose intense emission peaks at 484 and 575 nm. Dy3+ ion concentration is optimized to achieve the maximum light intensity in NCS phosphors. The concentration quenching is the consequence of energy transfer mechanism beyond 1.0 mol% (optimized) of the Dy3+ ion concentration, which was also examined in detail. The reckoned CIE coordinates (0.337, 0.346) for the optimized Dy3+:NCS phosphor located nearby standard white point coordinates, indicating the pure white light emission. Moreover, temperature-dependent luminescence studies express admirable thermal stability of as-made Dy3+:NCS phosphor as the emission intensity even at 423 K persists up to 77.26% of intensity at room temperature. Aforesaid results support the effective utilization of Dy3+ doped NCS phosphor in white LEDs. Highlights: Single-phase Dy3+ doped Na2CaSiO4 (NCS) phosphors synthesized via sol-gel method. CIE coordinates (0.337, 0.346) for Dy3+:NCS phosphor near to standard white point. As-synthesized Dy3+:NCS phosphor exhibits appreciable thermal stability. White light emission upon NUV excitation suggests its potential role in w-LEDs. [ABSTRACT FROM AUTHOR]

Crystalline divalent manganese-activated zinc orthosilicate (Zn2SiO4:Mn2+) nanophosphor has been synthesized via the solution-based sol-gel process. Structural, morphological, and photoluminescence (PL) properties were explored. X-ray diffraction pattern confirms the crystalline hexagonal structure of the single-phase Zn2SiO4 powder. The size and shape of Zn2SiO4 powder were analyzed using micrographs, which implies that the prepared phosphor particles are in the nano range. PL spectra have been recorded as a function of Mn2+ dopant concentration. A dominant green (~526 nm) emission broad peak was observed owing to the characteristic (4T1→6A1) transition of Mn2+ ion under UV/blue excitation. The green emission (~526 nm) intensity depends upon the doping concentration of Mn2+ ion, and it is found to be optimum for 2.0 mol%, after that quenching phenomenon was registered. The CIE color coordinate of Zn2SiO4:Mn2+ lies in the bright green region under UV excitation with 94.3% color purity. Real-time experiments have been carried out for speedy development of high-contrast fingermarks using Zn2SiO4 nanophosphor on various porous and nonporous substrates. [ABSTRACT FROM AUTHOR]

An orange-red (∼610 nm) emitting Sr3SiO5:Eu2+,Zn2+,Dy3+ long afterglow phosphor was synthesized using high temperature (1100 °C–1500 °C) based solid-state reaction method under controlled reducing atmosphere. X-ray diffraction (XRD) study confirms the tetragonal lattice structure having space group P4/ncc. Scherrer's size plot and Williamson-Hall methods have been applied to study the particle size distribution and inherent strain, respectively, using crystallographic data obtained from XRD patterns. Electron microscopy images showed the surface morphology with an average crystallite size of 0.412 μm. Furthermore, detailed luminescence study was performed to observe photoluminescence (PL) and afterglow characteristics. An optimal PL emission peak was registered at ∼610 nm when the phosphor was excited by visible blue (∼465 nm) light, which is due to the transitions from 4f65d¹ to 4f7 energy levels of Eu2+ ions. The enhanced afterglow property of >20 minutes has been achieved for dark-adapted human eyes, which could be utilized for designing strategic markings and signage boards that could glow in dark. [ABSTRACT FROM AUTHOR]

A facile method for feasible industrial production of long afterglow phosphor nanocomposites, in the form of small beads were developed that continuously emit visible light for >7 h to realize many innovative applications involving hard and soft surfaces. Green emitting SrAl2O4:Eu2+, Dy3+ (SRA) long afterglow phosphor was uniformly dispersed in the epoxy resin (ER) matrix in presence of organic surfactant as hardener to make phosphor-embedded viscous fluid that could then be solidified at room temperature (~25 °C) within few minutes. As ethyl alcohol (solvent) started evaporating, ethylene glycol (surfactant), which is the simplest amongst glycols, started adhering with SRA phosphor particles via van der Waals attraction. The homogeneity of dispersion strongly depends on the shape of SRA phosphor added to ER matrix and confirmed that the near-spherical is the best. The SRA phosphor–ER beads demonstrated an optimum ultraviolet (UV) excitation wavelength at 375 nm and a green-emission peak at 517 nm, where the latter one is due to the transitions from 4f65d1 to 4f7 energy levels of Eu2+ ions. The appearance of SRA phosphor–ER beads in translucent yellow-green color, bright green and green under ambient light, UV (375 nm) irradiation and in dark conditions, respectively was indicated using photoluminescence and colorimetric measurements. The SRA phosphor–ER beads exhibited highly durable, reversible and reproducible afterglow luminescence for longer durations. Photoluminescence, structural, morphological and afterglow properties of the prepared SRA phosphor–ER beads were investigated thoroughly. Moreover, these afterglow beads have several designing and crafting applications such as interior design, glowing toys, ornaments and tracking lights etc. [ABSTRACT FROM AUTHOR]

In the present study, CaZrO3 nanophosphors were sensitized with lanthanum (La) at different concentrations (0.5, 1.0, 1.5, 2.0, and 2.5) prepared using polyvinyl alcohol as the chelating agent through the sol–gel method. To study their structural and optical properties, samples were characterized by X‐ray diffractometry (XRD), field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM) and photoluminescence (PL). The XRD results revealed that samples were well crystallized and average crystallite sizes were calculated. The average crystallite size value was in good agreement with the value obtained from TEM analysis. Energy dispersive spectroscopy and FE‐SEM confirmed the existence of La in the prepared samples. In the PL spectra, La‐sensitized samples exhibited three bands at 402 nm, 438 nm, and 463 nm in the visible range when excited at the 260 nm wavelength. As the proportion of La increased, the intensity of bands at 438 nm and 463 nm decreased, whereas the band at 402 nm remained stable. Time‐resolved PL spectra illustrated the lifetime of the samples. Corresponding CIE co‐ordinates for La‐sensitized CaZrO3 were calculated. [ABSTRACT FROM AUTHOR]

Red emitting (~612 nm) CaTiO3:Pr3+ long afterglow nanocrystals with a persistence time ~20 min (dark adapted human eyes) have been synthesised for developing high contrast latent fingerprints using the sol-gel process. Due to the persistent emission, CaTiO3:Pr3+ nanophosphor does not require a continuous source for excitation, thereby eliminating the background information even from multi-colour substrates, resulting in a high signal to noise ratio. As a consequence of which, minute features of level- I, II and III can be clearly studied in high contrast fingerprints. Considerable blue shift (~20 nm) was recorded in photoluminescence excitation due to the quantum confinement properties of CaTiO3:Pr3+ nanocrystals. Powder x-ray diffraction confirms the formation of a single phase orthorhombic structure of CaTiO3:Pr3+ with average crystallite size ~40 nm. Spectral parameters indicate a very high color purity of 99% with CIE coordinates (0.62, 0.37) which are very close to NTSC standards for an ideal red-emission. Transmission electron microscopy studies confirm the formation of spherical particles with narrow size distribution which makes them suitable to combine with fingerprint development methods such as powder dusting and cyanoacrylate fuming methods. [ABSTRACT FROM AUTHOR]

The development of nanophosphors of desired sizes and properties for various practical applications and its growth in quantitative amounts inside the pores of an inorganic matrix is presented. By doing so, nanophosphors get surface passivated and are stabilized against environmental attacks. Accordingly, in the present study, the growth parameters for ZnS:Mn nanophosphors were systematically studied inside a SiO2 gel matrix, which can act as a capping agent as well. The samples were prepared using the sol-gel technique, followed by annealing at different temperatures to remove the trapped fluid inside the amorphous silica cage. Two categories of samples with lower (3.11×10-4) and higher (1.5×10-1) ZnS/SiO2 molar ratios were studied. The x-ray diffraction and scanning electron microscopy observations show that upon annealing, the nanocrystals grow in size and undergo a phase transition from cubic to hexagonal at temperatures between 700 and 900 °C. This is one of the very few known reports published on nano hexagonal ZnS formation. The observed phase transition is possibly the combined effect of the high-temperature (∼900 °C) and annealing-related compressive stress induced on the nano-ZnS by the silica cage. There has been formation of an intermediate metastable phase of the zinc silicate at annealing temperatures around 700 °C. The particle size distribution and emission properties were correlated using the optical absorption and photoluminescence (PL) results. The unannealed cubic nano-ZnS:Mn samples gave a broad PL, peaking at ∼585 nm, whereas the samples annealed at 900 °C for 5 h gave a narrow and sharp PL at ∼590 nm. This is attributed to the more efficient 4T1→6A1 transitions of Mn in the resultant hexagonal nano-ZnS matrix. [ABSTRACT FROM AUTHOR]

This paper reports the detailed synthesis mechanism and the structural, morphological and optical characterization of ultraviolet (∼311 nm) excitable samarium doped gadolinium yttrium orthovanadate, (Gd,Y)VO4:Sm3+, nanocrystals. X-ray diffraction and Rietveld refinement studies confirmed that the synthesized samples crystallize in a tetragonal structure with I41/ amd space group. The enhanced photoluminescence intensity of (Gd,Y)VO4:Sm3+ compared with the existing YVO4:Sm3+ phosphor clearly indicates the significant role of Gd3+ ions. This has been attributed to the sensitization of the 6 P J energy level of Gd3+ ions by energy transfer from orthovanadate (VO43−) ions and subsequent energy trapping by Sm3+ ions. The energy transfer from VO43− to Sm3+ via Gd3+ ions as intermediates and concentration quenching of Gd3+ luminescence are discussed in detail. The optical band gap of the as-prepared nanocrystals has been estimated using UV-vis-NIR absorption spectroscopy, which reveals a slightly higher band gap (3.75 eV) for YVO4 as compared to GdYVO4 (3.50 eV). Furthermore, confocal microcopy, decay parameters and Commission Internationale de l'Eclairage chromatic coordinates have supplemented these studies, which established the suitability of these nanophosphors for achieving spectral conversion in silicon solar cells. [ABSTRACT FROM AUTHOR]

A bulk sulphamic acid single crystal has been grown by a modified seed rotation technique. The lattice dimensions of the grown single crystal were confirmed using powder X-ray diffraction, and it was found that it crystallized in an orthorhombic structure with space group Pbca. The strain in the lattice was calculated by the Williamson-Hall equation. The crystalline perfection was examined by high-resolution X-ray diffraction and found to be extremely good (the single peak of the rocking curve having an FWHM of ∼8.0′′). The luminescence behaviour was recorded in the wavelength region between 400 and 630 nm using an Xe flash lamp which acts as an excitation source. The shock damage threshold was measured for the grown crystal in order to determine the mechanical capability of the title compound. The thermal parameter of sulphamic acid was calculated by photoacoustic spectroscopy. [ABSTRACT FROM AUTHOR]

In this work, we report enhanced power conversion efficiency (PCE) of bulk heterojunction polymer solar cells by Förster resonance energy transfer (FRET) from samarium-doped luminescent gadolinium orthovanadate (GdVO4:Sm3+) quantum dots (QDs) to polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) polymer. The photoluminescence emission spectrum of GdVO4:Sm3+ QDs overlaps with the absorption spectrum of PTB7, leading to FRET from GdVO4:Sm3+ to PTB7, and significant enhancements in the charge-carrier density of excited and polaronic states of PTB7 are observed. This was confirmed by means of femtosecond transient absorption spectroscopy. The FRET from GdVO4:Sm3+ QDs to PTB7 led to a remarkable increase in the power conversion efficiency (PCE) of PTB7:GdVO4:Sm3+:PC71BM ([6,6]-phenyl-C71-butyric acid methyl ester) polymer solar cells. The PCE in optimized ternary blend PTB7:GdVO4:Sm3+:PC71BM (1:0.1:1.5) is increased to 8.8% from 7.2% in PTB7:PC71BM. This work demonstrates the potential of rare-earth based luminescent QDs in enhancing the PCE of polymer solar cells. [ABSTRACT FROM AUTHOR]

Benzimidazole single crystals were grown using a vertical Bridgman technique with modified ampoule design. The thermal fluctuations during the melt were effectively controlled by the glass ampoule support which was filled with alumina wool in order to maintain a proper temperature gradient throughout the growth process. The unit cell dimensions of the grown crystals were assessed using powder X-ray diffraction technique. Comparative analyses have been carried out for both the crystals which were grown using a conventional ampoule and using the ampoule with support, via high resolution X-ray diffraction and it was found that there was a significant enhancement in crystalline perfection for the crystal which was grown using the ampoule with support. Further, optical transmission and photoluminescence studies on the grown crystals were carried out using UV-vis and photoluminescence spectroscopy and it was observed that there was a noticeable variation in the optical transmission and luminescence results. [ABSTRACT FROM AUTHOR]

A new rare-earth-free NaZnPO4:Mn2+ (NZP:Mn) phosphor powder has been developed by our group and investigated meticulously for the first time using secondary ion mass spectroscopy and chemical imaging techniques. The studies confirmed the effective incorporation of Mn2+ into the host lattice, resulting in an enhancement of photoluminescence intensity. Phase purity has been verified and structure parameters have been determined successfully by Rietveld refinement studies. The NZP:Mn phosphor powder exhibits strong absorption bands in the ultraviolet and visible (300-470 nm) regions with a significant broad yellow-green (~543 nm) emission due to the characteristic spin forbidden d-d transition (4T1→6A1) of Mn2+ ions, indicating weak crystal field strength at the zinc-replaced manganese site. The decay constants are a few milliseconds, which is a pre-requisite for applications in many display devices. The results obtained suggest that this new phosphor powder will find many interesting applications in semiconductor physics, as cost-effective light-emitting diodes (LEDs), as solar cells and in photo-physics. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Single-phase cool white-light emitting BaNb2O6:Dy3+ phosphors have been synthesized via a conventional solid-state reaction method and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) observations and spectrofluorophotometric measurements. XRD and Rietveld structural refinement studies confirm that all the samples exhibit pure orthorhombic structure [space group –C2221(20)]. SEM observations reveal the dense particle packaging with irregular morphology in a micron range. The as-prepared phosphors exhibit blue (482 nm) and yellow (574 nm) emissions under 349, 364, 386 and 399 nm excitations corresponding to 4F9/2→6HJ (J = 15/2, 13/2) transitions of Dy3+ ions. The energy transfer mechanism between Dy3+ ions has been studied in detail and the luminescence decay lifetime for the 4F9/2 level was found to be around 146.07 μs for the optimized phosphor composition. The calculated Commission Internationale de L'Eclairage (CIE) chromaticity coordinates for the optimized phosphor are (x = 0.322, y = 0.339), which are close to the National Television Standard Committee (NTSC) (x = 0.310, y = 0.316) coordinates. The values of CIE chromaticity coordinates and correlated color temperature (CCT) of 5907 K endorse cool white-light emission from the phosphor. The study reveals that BaNb2O6:Dy3+ phosphor could be a potential candidate for near ultra-violet (NUV) excited white-LED applications. [ABSTRACT FROM AUTHOR]

Nanostructured -doped (AZO) films are deposited on glass substrates by electroless deposition technique in the present work. AZO films with concentration from 1 at.% to 5 at.% are investigated for their structural and morphological properties by X-ray diffraction (XRD), and atomic force microscopy (AFM). An excellent homogeneity is achieved with average crystallite sizes of below 32 nm and a nearly constant root mean square (RMS) surface roughness between 1 nm and 3 nm, for various doping concentrations. These smooth and uniform films are characterized for their optical and photoluminescence (PL) properties. A higher value of average transparency between 79% and 92% in the wavelength range of 300-800 nm is achieved, and the PL intensity is found to be a strong function of doping. Density functional theory (DFT) calculations agree with the measured transmittance values, in addition to their predicted electronic structure. Moreover, time-resolved PL measurements indicate that the luminescence decay time decreases with increased doping concentration. [ABSTRACT FROM AUTHOR]

A single crystal of L-prolinium tartrate (LPT), which is an organic non linear optical material, was successfully synthesized and grown using a slow evaporation solution growth technique (SEST). The crystal structure and lattice parameters of the crystal were confirmed by powder X-ray diffraction and it was found that it belongs to the monoclinic crystal system with β = 100.380 and a noncentrosymmetric space group. The presence of strain in the grown ingot was calculated from powder X-ray diffraction measurements. The crystalline perfection was examined by high resolution X-ray diffractometry, which revealed that the crystal contained structural grain boundaries. The optical behavior of the grown specimen was analyzed by photoluminescence (PL) spectroscopy and its time resolved PL decay was calculated. The grown crystal adopted a step wise growth pattern with parallel striations, which was confirmed from the etching technique. Its ferroelectric and piezoelectric properties were also assessed. Its third order non linearity was assessed using an open aperture Z-scan technique. The thermal parameters of the LPT single crystal were calculated using a photopyroelectric technique. The mechanical strength of the single crystal at the micro level was observed by nanoindentation using the Oliver-Pharr method. [ABSTRACT FROM AUTHOR]

We present the results based on dielectric, electro-optical and photoluminescence (PL) measurements of a ferroelectric liquid crystal (FLC) doped with differently functionalised (–COOH, –OH and –NH2groups) multi-walled carbon nanotubes (MWCNTs). Functional group induced significant modifications in the dielectric permittivity (ε′), dielectric loss factor (tan δ), PL intensity and material parameters of MWCNT/FLC composites have been observed. We found that MWCNTs functionalised with –OH and –NH2have enhanced the dielectric properties and the PL intensity of FLC material remarkably. The observed results have been explained on the basis of the interaction between FLC material and functionalised MWCNTs. The present study is our sincere attempt to understand the effect of functionalisation of MWCNTs on the FLC properties. [ABSTRACT FROM PUBLISHER]

A potential semiorganic nonlinear optical material, L-alanine cadmium chloride monohydrate has been successfully synthesised and single crystals have been grown by slow evaporation solution growth technique at room temperature by using double distilled water as the solvent. The lattice dimensions of the grown crystal have been analysed by adopting powder X-ray diffraction technique and found that it crystallised in monoclinic system with space group C2. The crystalline perfection of the as-grown crystal has been assessed by high resolution X-ray diffraction and X-ray topography techniques and observed that the quality of the grown specimen is reasonably good. Its optical properties were examined by UV-Vis and photoluminescence techniques and found that there is no absorption in the entire visible range. Its functional groups were identified from FT-Raman and observed that there is no incorporation of other impurities during crystallisation. Its relative second harmonic generation efficiency has been tested with different particle size by Kurtz powder technique and found that within the coherence length the title compound is phase matchable. Its various thermal properties like thermal conductivity, specific heat, thermal effusivity, etc. have been evaluated by photopyroelectric technique and compared with other organic and inorganic materials. To confirm its piezoelectric response, its piezoelectric charge coefficient was measured using piezometer and found low. Its optical homogeneity as well as birefringence measurement of the grown specimen has been carried out by interferometric technique. The surface defects of the grown LACCM single crystal were analysed with etching at room temperature using water as an etchant. [ABSTRACT FROM AUTHOR]

A new ternary oxide Gd2CaZnO5 having interesting structural, mechanical, electronic and optical properties is synthesized and is studied in detail using density functional theory. The analysis revealed two polymorphs: orthorhombic and tetragonal; the orthorhombic phase was found to be the most stable structure under ambient conditions. A high-pressure (hydrostatic) phase transition to the tetragonal phase is predicted at about 4 GPa. This is one of very few reports that depict the phase transition of oxide materials under pressure. The calculated results are in agreement with the X-ray diffraction studies supported by Rietveld analysis. Analysis of the optical properties revealed both polymorphs to be direct-gap semiconductors with low dielectric constants. The calculated elastic constants of both phases satisfy the mechanical stability criteria. It is also identified that the half-filled 4f orbital of Gd induces a strong magnetic spin polarization in the host oxide lattice indicating that the material could be effectively used in versatile applications ranging from biomedical devices to light emitting diodes. [ABSTRACT FROM AUTHOR]

We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001) substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 x 108 cm-2 at 750 °C) than that of the low temperature grown sample (1.1 x 109 cm-2 at 730 °C). A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films. [ABSTRACT FROM AUTHOR]

There has been a stringent demand for blue (∼450 to 470 nm) absorbing and red (∼611 nm) emitting material systems in phosphor converted white light emitting diodes (WLEDs) available in the market. The conventionally used red-emitting Y2O3:Eu3+ phosphor has negligible absorption for blue light produced by GaInN based LED chips. To address this issue, a new red-emitting Gd2CaZnO5:Eu3+ (GCZO:Eu3+) nanophosphor system having exceptionally strong absorption for blue (∼465 nm) and significant red (∼611 nm) photoluminescence is presented. This is attributed to a dominant f–f transition (5D0→7F2) of Eu3+ ions, arising due to an efficient energy transfer from the Gd3+ sites of the host lattice to Eu3+ ions. The external quantum yield (QY) measured at 465 nm absorption and 611 nm emission revealed that the GCZO:Eu3+ nanophosphor has better QY of 23% as compared to commercial Y2O3:Eu3+, which is ＜1%. X-ray diffraction and microscopy observations showed the nanocrystalline nature and slightly elongated morphology of the sample, respectively. While the energy dispersive X-ray analysis identified the chemical constituents of the GCZO:Eu3+ nanophosphor, the color overlay imaging confirmed the substitution of Eu3+ for Gd3+ ions. As seen from the QY statistics it is highly anticipated that the multifold absorption at ∼465 nm would certainly improve the color rendering properties of existing WLEDs. [ABSTRACT FROM AUTHOR]

ABSTRACT We have synthesized and characterized a new BaCa2Al8O15:Eu2+,Dy3+ phosphor prepared by the combustion method. X-ray diffraction, thermoluminescence, scanning electron microscope, time decay and optical spectral analysis photoluminescence excitation, emission spectra were used to characterize the phosphors. Broadband ultraviolet excited luminescence of the BaCa2Al8O15:Eu2+,Dy3+ was observed in the blue region (λmax = 435 nm) due to transitions from the 4f65d1 to the 4f7 configuration of the Eu2+ ion. Scanning electron microscopy has been used for exploring the morphological properties of the prepared phosphors. The BaCa2Al8O15:Eu2+ phosphor has a blue afterglow when Dy3+ ions were co-doped. The thermoluminescence spectra show that the Dy3+ ion induces a proper trap in the phosphor with a depth of 0.67 eV and results in a long afterglow phosphorescence. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The results pertaining to faster electro-optic response time and improved photoluminescence (PL) of BaTiO3 nanoparticles (BT NPs) doped ferroelectric liquid crystal (FLC) are presented. The observed increase (∼2 fold) in PL intensity and simultaneous reduction of response time have been achieved for an optimal BT NPs doping of 0.2 wt. %. These are attributed to the large dipole moment of BT that couples effectively with that of FLC molecules. These studies would provide benchmark for realization of high luminescent FLC devices that are faster in response. [ABSTRACT FROM AUTHOR]

Time evolution photoluminescence (PL) studies of ferroelectric liquid crystal (FLC) mixtures doped with different concentrations of ZnS and CdS quantum dots (QDs) are carried out. Remarkable enhancement in the PL intensity and a significant shift in the emission band of FLC materials are observed by doping with a suitable amount of QDs. The modifications in the PL behaviour of the QD/FLC composites are found to depend strongly on time, and also on the QD/FLC mixtures themselves. The enhancement in the PL intensity of the FLC materials is attributed to the additive combination of the emissions from FLCs and QDs and the highly scattering phase of the FLC materials used. The shifting of the emission band and reduction in the PL intensity of the QD/FLC composites could be attributed to the oxidation of QDs. The observed results would be helpful in selecting QD/FLC composites to observe stable and enhanced PL from composites. [ABSTRACT FROM AUTHOR]

As-synthesized deformed helix ferroelectric liquid crystal (FLC) material with high spontaneous polarization and rotational viscosity is characterized. The FLC material is then systematically doped with various noble metal nanoparticles (MNPs) such as Ag, Au, and Pt in the size range of 5 nm. The optical behavior of MNP doped FLC material is studied via electro-optic and photoluminescence measurements. The observed optical response has been discussed on the basis of the interaction of plasmons in MNPs with the electromagnetic wave from the incident light that traverses through the FLC molecules. [ABSTRACT FROM AUTHOR]

We report the enhancement in photoluminescence (PL) intensity and shift in spectral energy band of ferroelectric liquid crystal (FLC) doped with ZnS quantum dots (QDs). The emission from ZnS QDs has combined constructively with that of FLC to give enhanced PL intensity. On the other hand, the smectic phases of FLC provided strong light scattering and hence improved the PL intensity of the composite. The change in effective refractive index of FLC due to different concentrations of ZnS QDs has caused the red shift. Our observations will certainly provide a promising tool in the realization of enhanced PL-LC display devices. [ABSTRACT FROM AUTHOR]

Eu3+ luminescence spectroscopy has been used to investigate the effective doping of alkoxide-based silica (SiO2) gels using a novel pressure-assisted sol-gel method. Our results pertaining to intense photoluminescence (PL) from gel nanospheres can be directly attributed to the high specific surface area and remarkable decrease in unsaturated dangling bonds of the gel nanospheres under pressure. An increased dehydroxylation in an autoclave resulted in enhanced red (~611 nm) PL emission from europium and is almost ten times brighter than the SiO2 gel made at atmospheric pressure and ~50. using conventional Stöber-Fink-Bohn process. The presented results are entirely different from those reported earlier for SiO2:Eu3+ gel nanospheres and the origin of the enhanced PL have been discussed thoroughly. [ABSTRACT FROM AUTHOR]

Zinc oxide doped with europium has been prepared by high temperature calcination method using ZnO, Eu2O3, and LiOH. Structural characterization by X-ray diffraction and optical studies by photoluminescence spectroscopy together give evidence that Eu3+ is going to the substitutional site of Zn2+. The concentration of chemicals used, sintering temperature, and time are optimized with photoluminescence excitation spectroscopy for a sharp and intense red signal which is a signature of Eu3+. Characteristic red emission at 607 nm is observed using high-energy excitation along with the native deep center emission of ZnO peaking around 525 nm. [ABSTRACT FROM AUTHOR]

Aluminum oxide, a promising material for high temperature applications, is synthesized by combustion route and characterized by X-ray diffraction technique. Photoluminescence of aluminum oxide bombarded with 120 MeV swift Au9+ ions have been studied at room temperature. The observed PL emission with peak at ∼420 nm is attributed to F-center while the two more weak emissions with peaks at ∼482 and ∼525 nm are attributed to aggregates of F-centers. It is found that PL intensity increases with increase in Au9+ ion fluence up to ∼1×1013 ions cm-2 and thereafter it reaches saturation. The Fourier transform Infrared spectroscopy results show the destruction of Al-O-H bonds whereas the XRD results indicate the surface amorphization of Al2O3. [ABSTRACT FROM AUTHOR]

Solid-state preparation, structure, and multi-colour luminescence of Eu2+ doped strontium aluminate (SRA) phosphors have been reported in this paper. It has been observed that a slight modification in the processing parameters such as type of reducing atmosphere, stoichiometric excess of one or more constituents, nature of fluxes, and intentional addition of carbon or rare-earth halides can drastically shift the emission colours of the SRA phosphor in the visible spectrum. X-ray diffraction analysis and scanning electron microscopy observations of the samples revealed the formation of different crystalline phases related to the SRA system. The luminescence measurements showed that the decay times varied with the emission colours of the samples. [ABSTRACT FROM AUTHOR]

In the present paper, the experimental results on some physical properties of silica aerogels modified by four different drying control chemical additives (DCCAs): (i) oxalic acid (OXA), (ii) glycerol (GLY), (iii) N,N-dimethylformamide (DMF) and (iv) formamide (FA) are reported. The molar ratio of tetramethoxysilane (TMOS), methanol (MeOH), water (H2O) and ammonia (NH4OH) was fixed at 1 : 12 : 4 : 3.6 × 10−3 respectively, throughout our experiments, and the DCCA/TMOS molar ratio was varied accordingly. The DCCA/TMOS molar ratio at around 0.4 was found to be the limiting value for almost all the modified aerogels, above which the cracking probability of the aerogels increased drastically. Further, the DCCA modified aerogels were characterized by optical transmittance and porosity measurements. Physical properties such as bulk density, volume shrinkage and specific surface area were also determined for all the modified aerogels. The pore size distribution (PSD) was found to shift towards smaller pore radii for acidic (OXA) DCCA and larger pore radii for basic (FA, DMF) DCCAs. The results have been supported by particle and pore sizes observed using Scanning Electron Microscopy (SEM) and BET analysis. [ABSTRACT FROM AUTHOR]

To optimize and produce silica aerogels with high direct transmittance and low diffusive values, systematic and detailed experiments were carried out on the effect of sol-gel processing parameters on optical properties of silica aerogels. A series of aerogel samples of different molar ratio combinations was optically examined in the UV-visible-NIR range by a spectrophotometer equipped with an integrating sphere. The overall transmittance of the aerogels in the visible range varied from 75 to 93% depending upon the molar ratio combination. The most relevant parameter being studied was the direct/hemispherical transmittance ratio (τ). The best value of τ obtained for an aerogel in the present study was about 93% with a molar ratio of 1 TMOS: 12 MeOH:4 HO:3.5 × 10 NHOH, respectively. Apart from visible transparencies, solar energetic transparencies of some silica aerogels were also measured and reported. These optical data, together with the porosity measurements, allowed us to improve the process of fabrication of low-diffusing aerogel material. The experimental results are discussed considering the percentage of porosity and heterogeneity generated in pore size distributions due to the variation of sol-gel processing parameters. [ABSTRACT FROM AUTHOR]

In the present paper, the experimental results on the influence of catalyst (citric acid) concentration on the physical properties of TEOS silica aerogels, are reported. The aerogels have been prepared by hydrolysis and polycondensation of tetraethoxysilane (TEOS) using citric acid (CTA) as a new catalyst followed by supercritical drying in an autoclave. In order to obtain the best quality silica aerogels in terms of monolithy, high transparency, low density, large surface area and high porosity with uniform pore size distribution, the catalyst concentrations were varied from 0.0005 M to 0.1 M by keeping the molar ratio of TEOS : EtOH : H2O constant at 1 : 5 : 7, respectively. It has been found that the lower (<0.001) CTA concentration resulted in low density, smaller surface area but opaque aerogels whereas higher (>0.005 M) CTA concentration resulted in high density, large surface area, highly transparent but cracked aerogels. On the other hand, medium (between 0.001 and 0.005 M) CTA concentration resulted in monolithic, low density, large surface area and highly transparent silica aerogels. The pore size distribution (PSD) for higher (0.1 M) and lower (0.0005) CTA concentrations shifted towards smaller and larger pore radii respectively, whereas for medium (0.001 M) CTA concentration, the PSD is narrow and uniform, which reduces the differential pressure during supercritical solvent extraction leading to monolithic silica aerogels. These results have been supported and discussed by considering the particle and pore sizes observed by Scanning Electron Microscopy (SEM). The surface area was measured by BET analysis. [ABSTRACT FROM AUTHOR]

The detailed surface analysis such as survey scan, core-level, and valence band spectra of highly luminescent ZnO:Na nanocrystals were studied using the x-ray photoelectron spectroscopy to establish the performed presence of Na+ ions. The observed increase in band gap from 3.30 (bulk) to 4.16 eV (nano), is attributed to the quantum confinement of the motion of electron and holes in all three directions. The photoluminescence and decay measurements have complemented and supported our study to design an efficient and ultrafast responsive optical sensing device. [ABSTRACT FROM AUTHOR]

Carbon nanofiber (CNF) with springlike and double-helix structures has been synthesized by catalytic thermal pyrolysis of an acetylene precursor at 850–950 °C using iron nanopowder and thiophene as catalyst and promoter, respectively. High resolution electron microscopy revealed a higher d-spacing (∼3.46 Å) of (002) crystal plane than customary multiwalled carbon nanotube (MWCNT) (3.37 Å) that helps in sustaining mechanical shocks better than MWCNTs. The large surface to volume ratio of springlike CNF does provide many delocalized free electrons to enhance the photoluminescence activity. Electron paramagnetic resonance signal showed a single narrow line having g-value 2.0024±0.0002 and spin contribution 3.4956×10-16 spins/g. [ABSTRACT FROM AUTHOR]

A method of dispersing YVO4:Eu quantum dots (QDs) as uniform two-dimensional (2D) layers with a high degree of homogeneity is presented. Annealing at 773 K resulted in coalescence of QDs to form nanoclusters with size of ∼25 nm with an improved photoluminescence and ∼80% transmittance at 800 nm. An efficient 5D0-7F2 transition and lifetimes of ∼1038 μs for the characteristic Eu3+ emission were observed. The absorption and emission peaks showed a slight blueshift, due to quantum-size effect, as compared to that for the bulk counterpart. Our method of 2D layer deposition is useful to enhance spectral response of the solar cells. [ABSTRACT FROM AUTHOR]

High brightness zinc oxide quantum dots were made with intentional alkali metal doping using quantum-confined atom model. The tuning of emission spectrum in the range of 480–562 nm was achieved by dispersing them in solvents with varying index of refraction. The observed emission bands are quite distinct from the nonstructured green emission of zinc oxide at 2.4 eV (515 nm) but are attributed to donor-acceptor recombination involving the zinc vacancy and Li+/Na+, or the modifications assigned to the surface states by the surrounding medium. The photoluminescence shifts are found to be sensitive to refractive index term n2-1/2n2+1 useful for practical applications. [ABSTRACT FROM AUTHOR]