Simple and Cost-effective Synthesis of a Rare-earth Free Long Afterglow Phosphor for Dark Visual Markings.

Materials with long afterglow (LAG) became very renowned in the field of luminescence due to their high ability to store energy. However, the development of LAG phosphors is mostly dependent on rare-earth activators, which are commercially expensive due to their limited availability across the world. On the other hand, LAG phosphors that are not based on rare-earth and are developed as an alternative cannot compete with existing rare-earth LAG phosphors. Copper-doped zinc sulfide (ZnS:Cu) phosphor developed long ago has considerable afterglow, but its development has been too tedious, and expensive, and contains usage of toxic gasses such as H2S, CS2, etc. and most of the literature refers to the cubic phase of ZnS. To overcome these issues and simplify the process, we have developed a cost-effective approach to synthesize the hexagonal phase of ZnS, without the involvement of hazardous gases. This is one of the very few reports that highlights the appearance of LAG phenomenon from the hexagonal ZnS:Cu phosphor system. Structural, morphological, and optical studies of the developed ZnS:Cu LAG phosphor have been carried out. The phosphor showed a strong green photoluminescence at 515 nm and an afterglow duration of ~ 1 h useful for specific applications of visual markings in dark conditions. The thermoluminescence spectrum shows a broad and intense glow peak at 377.15 K that indicates the electron trap depth to be at 0.75 eV, supporting our afterglow results.

Voltage- and Power-Conversion Performance of Bi-functional ZrO2 : Er3+ / Yb3+ Assisted and Co-sensitized Dye Sensitized Solar Cells for Internet of Things Applications.

Giant power conversion efficiency is achieved by using bifunction ZrO2 : Er3+ /Yb3+ assisted co-sensitised dye-sensitized solar cells. The evolution of the crystalline structure and its microstructure are examined by X-ray diffraction, scanning electron microscopy studies. The bi-functional behaviour of ZrO2 : Er3+ /Yb3+ as upconversion, light scattering is confirmed by emission and diffused reflectance studies. The bi-function ZrO2 : Er3+ /Yb3+ (pH=3) assisted photoanode is co-sensitized by use of N719 dye, squaraine SPSQ2 dye and is sandwiched with Platinum based counter electrode. The fabricated DSSC exhibited a giant power conversion efficiency of 12.35 % with VOC of 0.71 V, JSC of 27.06 mA/cm2 , FF of 0.63. The results, which motivated the development of a small DSSC module, gave 6.21 % and is used to drive a tiny electronic motor in indoor and outdoor lighting conditions. Small-area DSSCs connected in series have found that a VOC of 4.52 V is sufficient to power up Internet of Things (IoT) devices.

Noninvasive treatment of psoriasis and skin rejuvenation using an akermanite-type narrowband emitting phosphor.

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 [Ca2 MgSi2 O7 :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.

Review on long afterglow nanophosphors, their mechanism and its application in round-the-clock working photocatalysis.

Semiconductor assisted photocatalysis is one of the most efficient methods for the degradation of complex organic dyes. A major limiting factor of semiconductor assisted photocatalysis is the requirement of a continuous source of light to perform a redox reaction. One of the upcoming solutions is photon energy-storing long afterglow/persistent phosphors. They are an unusual kind of rechargeable, photon energy capturing/trapping phosphors that can trap charge carriers (electrons/holes) in their meta-stable energy levels, thereby resulting in persistent luminescence. Persistence luminescence from such materials can range from minutes to hours. The coupling of long afterglow phosphors (LAP) with the conventional semiconductor is a promising way to support the photocatalytic process even in dark. In addition, dissimilar band structures of LAPs and semiconductor results in formation of heterojunction which further suppresses the recombination of charge. Such an encouraging idea of LAP for round-the-clock working photocatalytic system is in its premature stage; which is required to be investigated fully. Thus, we present a state-of-art review on the potential materials for assisting round-the-clock photocatalysis, trapping-detrapping mechanism in LAP materials, fabrication strategies and their associated characterization tools. Review also covers LAP materials and their photocatalytic mechanism briefly.

Phytochemical analysis of Moringa Oleifera leaves extracts by GC-MS and free radical scavenging potency for industrial applications.

Natural extracts have been of very high interest since ancient time due to their enormous medicinal use and researcher's attention have further gone up recently to explore their phytochemical compositions, properties, potential applications in the areas such as, cosmetics, foods etc. In this present study phytochemical analysis have been done on the aqueous and methanolic Moringa leaves extracts using Gas Chromatography-Mass spectrometry (GCMS) and their free radical scavenging potency (FRSP) studied using 2, 2-diphenyl-1-picrylhydrazyl (DPPH) free radical for further applications. GCMS analysis revealed an extraction of range of phytochemicals in aqueous and methanolic extracts. In aqueous, extract constituents found with high percent peak area are Carbonic acid, butyl 2-pentyl ester (20.64%), 2-Isopropoxyethyl propionate (16.87%), Butanedioic acid, 2-hydroxy-2-methyl-, (3.14%) (also known as Citramalic acid that has been rarely detected in plant extracts) and many other phytochemicals were detected. Similarly, fifty-four bio components detected in methanolic extract of Moringa leaves, which were relatively higher than the aqueous extract. Few major compounds found with high percent peak area are 1,3-Propanediol, 2-ethyl-2- (hydroxymethyl)- (21.19%), Propionic acid, 2-methyl-, octyl ester (15.02%), Ethanamine, N-ethyl-N-nitroso- (5.21%), and 9,12,15-Octadecatrienoic acid etc. FRSP for methanolic extract was also recorded much higher than aqueous extract. The half-maximal inhibitory concentration (IC50) of Moringa aqueous extract observed is 4.65 µl/ml and for methanolic extract 1.83 µl/ml. These extracts can act as very powerful antioxidants, anti-inflammatory ingredient for various applications in diverse field of food, cosmetics, medicine etc.

Investigation of lanthanum-sensitized CaZrO3 blue nanophosphors for white light-emitting diode applications.

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.

Red emitting CaTiO3: Pr3+ nanophosphors for rapid identification of high contrast latent fingerprints.

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.

Self-Activated Green-Yellow Emitting Gd2CaZnO5 Phosphor for Efficient Ultra-Violet Light-Emitting Diodes.

A new self-activated green-yellow emitting Gd2CaZnO5 (GCZO) phosphor was synthesized using solid-state reaction method at high-temperature. XRD analysis confirmed the orthorhombic structure of the sample with the Pbnm space group. SEM micrographs reveal the irregular morphology with micron sized particles. Detailed photoluminescence (PL) analysis revealed that the excitation of the phosphor lies in the UV range (˜377 nm) with the related broad green-yellow emission centered at 530 nm. The broad band emission ranging from ˜450 nm to 650 nm can be attributed to the surface defects and oxygen vacancies. The calculated luminescence decay lifetime for the optimized phosphor was found to be 2.925 µs. Furthermore, the color-coordinate (x, y) were calculated and found to be (0.44, 0.45), which lies in the green-yellow (˜540 nm) region of the electromagnetic spectrum. The values of color coordinates and Color correlated temperature of 3289 K support the synthesized phosphor for the emission of warm white-light. These results perfectly established the suitability of this green-yellow emitting GCZO phosphor for Ultra-Violet Light-Emitting Diodes (LEDs) excited white-LED applications.

Size-Selective ZnO Nanocrystals as Spectral Energy Converters for Use in Advanced Display Devices.

In this paper, we report the synthesis of size-selective zinc oxide (ZnO) nanocrystals by three different techniques namely, auto-combustion, co-precipitation and atomizer and their effective energy conversion from harmful ultra-violet (UV, 365 nm) to visible green light. All the three methods are facile and convenient for the controlled synthesis of ZnO nanocrystals with an average crystallite size ranging 12-35 nm. The structural characterization using XRD revealed that the phase of ZnO nanocrystals was wurtzite. The morphology of the ZnO nanocrystals in all the three cases was found to be spherical and uniform as determined by High Resolution Transmission Electron Microscope. The novelty of the current work is to synthesize highly luminescent ultra-small ZnO nanocrystals without any dopant and their possible use as efficient spectral converters in displays. This result is further supported by steady-state photoluminescence spectra recorded under UV (365 nm) radiation as excitation. The presence of quantum confinement effect and increased surface to volume ratio perfectly established that ZnO nanocrystals synthesized by various routes have significant impact in the fields of optoelectronics, biomedical fields and advanced active display devices.

Unusual Red-Shift and Enhanced Photoluminescence of BaMgAl10O17:Eu2+ Phosphor Under Ultraviolet A Excitation for Modern Lighting Systems.

An unconventional red-shift but enhanced photoluminescence (PL) under ultraviolet A (UV-A) irradiation of Eu2+ doped Barium Magnesium Aluminate (BAM) phosphor prepared in both bulk and nanoforms useful for modern lighting applications has been presented. The solid-state reaction and solution combustion approaches were used for the preparation of phosphors with post-annealing step in reduced atmosphere. A significant broad blue-green (˜500 nm) PL associated with the transition of Eu2+ from 4f6 5d1 excited state to the 4f7 ground state has been observed. The observed shifts and PL intensities were found to be extremely reliant on the thermal processing parameters during the synthesis of phosphor/nanophosphormaterials. It's also important to note that the size of the phosphor particles have significant role in defining the red-shift of PL due to quantum confinement effect. Detailed structural and morphological characterizations were also done in this paper. The results are promising and suggest that the BAM phosphor is highly desirable for enhancing the brightness levels in modern lighting and display systems.

Interfacial behavior of confined mesogens at smectic-C*-water boundary.

In this paper, we have investigated the behavior of mesogens at smectic-C*-water interface confined in a liquid crystal (LC) cell with interfacial geometry. Polarized optical microscopy was used to probe the appearance of various smectic-C* domain patterns at water interface owing to the reorientation of mesogens. The undulated stripe domains observed at the air interface of smectic-C* meniscus vanished as the water entered into the smectic layers and focal conical domain patterns appeared at smectic-C*-water boundary. A spatially variable electro-optical switching of LC molecules was also observed outside the electrode area of the interfacial cell. The electrode region at the interface, as well as on the water side, was damaged upon application of an electric field of magnitude more than 150 kV/m. The change in dielectric parameters of mesogens was extensively studied at interface after evaporating the water. These studies give fundamental insights into smectic-C*-water interface and also will be helpful in fabricating better LC devices for electro-optical and sensing applications.

Luminescence and advanced mass spectroscopic characterization of sodium zinc orthophosphate phosphor for low-cost light-emitting diodes.

A new rare-earth-free NaZnPO4:Mn(2+) (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 Mn(2+) 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 ((4)T1→(6)A1) of Mn(2+) 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.

Emerging cool white light emission from Dy(3+) doped single phase alkaline earth niobate phosphors for indoor lighting applications.

Single-phase cool white-light emitting BaNb2O6:Dy(3+) 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 (4)F9/2→(6)HJ (J = 15/2, 13/2) transitions of Dy(3+) ions. The energy transfer mechanism between Dy(3+) ions has been studied in detail and the luminescence decay lifetime for the (4)F9/2 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:Dy(3+) phosphor could be a potential candidate for near ultra-violet (NUV) excited white-LED applications.

Assessment on third order non linearity and other optical analyses of L-Asparagine Monohydrate single crystal: An efficient candidate for harmonic conversions.

Single crystal of l-Asparagine Monohydrate, an organic material has been successfully grown by slow evaporation solution growth technique at ambient condition. The lattice parameters and its strain of the grown crystal have been evaluated from powder X-ray diffraction and found that it belongs to orthorhombic crystal system. The polarizability has been measured by using the Clausius-Mossotti relation. The crystalline perfection of grown single crystal has been examined by high resolution X-ray diffraction and its imperfection in the diffraction plane was clearly visible by recording topographical image of the plane. From the high resolution XRD, it confirms that the crystal contained high crystalline perfection. The optical behavior was analyzed by photoluminescence and birefringence methods. In the photoluminescence, a broad peak has been observed at 475 nm which suggest that it emits blue light. The decay tendency of the material has also been observed by calculating decay constant. The optical homogeneity has been determined by the dispersion pattern of the material. The two photon absorption coefficient was further calculated by Z-scan, which gives the information about the third order non linear optical behavior of the material. The value of two-photon absorption coefficient is 4.25 × 10(-12)m/W. The thermal parameters like thermal effusivity, thermal diffusivity, specific heat and thermal conductivity was obtained by using photopyroelectric technique. The ferroelectric behavior of the grown specimen was analyzed from PE (polarization VS electric field) loop. The loop suggests that the material was a nearly equivalent to ideal capacitor.

Probing the dynamics of geometrically confined ferroelectric mesogens at the air interface.

This article focuses on the alignment and dynamics of mesogens at the ferroelectric liquid crystal (FLC)/air interface in a confined geometry. The interface has been systematically prepared and characterised with provision for applying an electric field separately to the bulk and air interface of the FLC. Polarizing optical microscopy (POM) investigations done at the FLC/air interface have exposed the concave geometry, cell thickness dependent boundary width and phase dependent optical textures of the FLC meniscus at the interface. Dielectric spectroscopy investigations revealed the presence of an additional molecular relaxation mode at the FLC/air interface, which is attributed to the short axis rotation of homeotropically aligned mesogens at the interface. Based on the observations from the POM, dielectric spectroscopy and X-ray diffraction profiles, we schematically envisaged the molecular arrangement and dynamics of the FLC/air boundary. These studies would be helpful for innovations in liquid crystal based devices and also for many other applications, where soft surfaces, interfaces and confinement play a momentous role.

Optical studies of Sm³âº ions doped zinc alumino bismuth borate glasses.

Zinc Alumino Bismuth Borate (ZnAlBiB) glasses doped with different concentrations of samarium (Sm(3+)) ions were prepared by using melt quenching technique and characterized for their lasing potentialities in visible region by using the techniques such as optical absorption, emission and emission decay measurements. Radiative properties for various fluorescent levels of Sm(3+) ions were estimated from absorption spectral information using Judd-Ofelt (JO) analysis. The emission spectra and con-focal photoluminescence images obtained by 410 nm laser excitation demonstrates very distinct and intense orange-red emission for all the doped glasses. The suitable concentration of Sm(3+) ions in these glasses to act as an efficient lasing material has been discussed by measuring the emission cross-section and branching ratios for the emission transitions. The quantum efficiencies were also been estimated from emission decay measurements recorded for the (4)G5/2 level of Sm(3+) ions. From the measured emission cross-sections, branching ratios, strong photoluminescence features and CIE chromaticity coordinates, it was found that 1 mol% of Sm(3+) ions doped ZnAlBiB glasses are most suitable for the development of visible orange-red lasers.

Bulk growth of ninhydrin single crystals by solvent evaporation method and its characterization for SHG and THG applications.

Ninhydrin is a well-known compound generally used in amino acid synthesis and also for detecting the latent fingerprints on porous surfaces. Single crystals can be grown by dissolving the compound in double distilled water at ambient temperature, and can be used as a potential material for second and third harmonic generation applications. The grown specimen was subjected to different characterization techniques in order to find out its suitability for device fabrication. Its lattice dimensions have been confirmed by X-ray powder diffraction and its crystalline quality has been assessed by high resolution X-ray diffraction and X-ray topography methods. The presence of functional groups was identified from HETCOR analysis and confirmed the absence of impurities during crystallization. Its optical properties have been examined by photoluminescence and birefringence analyses. Its thermal parameters such as thermal diffusivity, thermal conductivity and specific capacity have been carried out by following photopyroelectric method. Third order nonlinear optical measurements have been carried out using Z-scan technique and its nonlinear optical absorption coefficient has been determined.

Synthesis and characterization of blue long-lasting BaCa2Al8O15:Eu2+, Dy3+ phosphor.

We have synthesized and characterized a new BaCa2Al8O15:Eu(2+),Dy(3+) 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:Eu(2+),Dy(3+) was observed in the blue region (λ(max) = 435 nm) due to transitions from the 4f(6)5d(1) to the 4f(7) configuration of the Eu(2+) ion. Scanning electron microscopy has been used for exploring the morphological properties of the prepared phosphors. The BaCa2Al8O15:Eu(2+) phosphor has a blue afterglow when Dy(3+) ions were co-doped. The thermoluminescence spectra show that the Dy(3+) ion induces a proper trap in the phosphor with a depth of 0.67 eV and results in a long afterglow phosphorescence.

Crystalline perfection, optical and third harmonic generation analyses of non-linear optical single crystal of L-lysine acetate.

The potential organic non-linear optical single crystal of L-lysine acetate has been grown by slow evaporation solution growth technique (SEST) at room temperature. It crystallizes in the monoclinic system with space group of P2(1). The crystalline perfection of the grown single crystal has been examined by high resolution X-ray diffraction analysis (HRXRD). The functional groups of the synthesized compound have been identified by (13)C NMR, (1)H NMR and FTIR analyses. The optical absorption studies show that the crystal is transparent in the entire visible region with a cut-off wavelength of 236 nm. The optical band gap is found to be 5.29 eV. The steady-state PL spectra was recorded for pure L-lysine acetate crystal at room temperature. The third harmonic generation efficiency of the crystal has been evaluated by Z-scan technique and its non-linear optical coefficient has been calculated. Birefringence measurement has been carried out in order to see the optical homogeneity of the grown specimen. Its electrical properties has been assessed by dielectric measurement at different temperatures. The calculated optical band gap is 5.29 eV. Its thermal parameters like thermal diffusivity (α), thermal effusivity (e), thermal conductivity (k) and heat capacity (C(p)) have been determined by photopyroelectric technique. Vickers micro hardness studies were carried out using a Vickers hardness tester equipped with a diamond square indenter. The piezoelectric measurement for L-lysine acetate has been also been carried at ambient condition.

Fabrication and electro-optic properties of a MWCNT driven novel electroluminescent lamp.

We present a novel, cost-effective and facile technique, wherein multi-walled carbon nanotubes (CNTs) were used to transform a photoluminescent material to exhibit stable and efficient electroluminescence (EL) at low voltages. As a case study, a commercially available ZnS:Cu phosphor (P-22G having a quantum yield of 65 ± 5%) was combined with a very low (~0.01 wt%) concentration of CNTs dispersed in ethanol and its alternating current driven electroluminescence (AC-EL) is demonstrated. The role of CNTs has been understood as a local electric field enhancer and facilitator in the hot carrier injection inside the ZnS crystal to produce EL in the hybrid material. The mechanism of EL is discussed using an internal field emission model, intra-CNT impact excitation and the recombination of electrons and holes through the impurity states.