Elements Of X Ray Diffraction

New red emitting phosphors NaSrLa(MO4)3:Eu3+ [M = Mo and W] for white LEDs: Synthesis, structural and optical study

Sunlight-driven activation of peroxymonosulfate by microwave synthesized ternary MoO3/Bi2O3/g-C3N4 heterostructures for boosting tetracycline hydrochloride degradation

Synthesis of layered 2H–MoSe2 nanosheets for the high-performance supercapacitor electrode material

Optical nanomaterials (ONMs) have attracted significant attention of the global research community owing to their several superior advantages. Some of the ONMs depict negligible photobleaching, bright emission, large electron-hole overlap integral, ease of coating on any surface, large Stoke/Antistoke shifts, higher photostabilites, easy to incorporate inside human body etc. These properties make them technologically highly efficient which helps in minimizing the global issue of energy crisis and improving the standard of living of common man. Several aspects of ONMs such as plasmonic nanomaterials, quantum dots, photonic crystals, and rare earth doped nanoparticles have been discussed. For covering various categories of luminescent nanomaterials (LNMs) based on composition, a brief introduction and importance of metal nanoclusters, carbon nano dots, organic-inorganic nanocomposites, and metal doped nanoparticles have been also included. This review article gives very concise overview of rare earth doped oxide nanoparticles covering several important aspects such as rare earth ion (RE) as dopant, oxide-based host, nanophosphors etc. The importance of LNMs, their advantages as well as drawbacks are also highlighted. Technologically important types of RE doped oxide nanoparticles pertaining to downconversion, upconversion, persistence and radioluminescence are also explained and covered in detail in this review article. Several recent applications involving LNMs in bioimaging, solar cell, thermal sensor, biosensor, anti-counterfeiting etc are explained. In the last section of the review, a comparison between nano and bulk rare earth doped oxide LNMs are discussed in terms of several photophysical properties such as dopant local symmetry, Stark splitting, emission intensity, luminescence lifetime, host to dopant energy transfer, quantum yield etc. Finally, this review article is concluded with summary, outlook, challenges, and future scope on the use of LNMs. Several important aspects of LNMs with focus on RE doped oxide nanoparticles have been covered in this review article which will help general readers in their further research, in this important area, for development of both fundamental sciences and applications involving LNMs.

Optical nanomaterials with focus on rare earth doped oxide: A Review

This study reports the synthesis of nanocrystalline undoped and europium doped BaWO4:Eu3+ nanophosphors by a mechanical activation process using high energy ball mill (HEBM) technique. The prepared nanophosphors were characterized systematically by Rietveld analysis of the X-ray powder diffraction (XRD) data, Raman spectroscopy, energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The synthesized nanophosphors were found to possess spherical morphology and small particle sizes ∼25 nm. To explore this material for application in luminescence, detailed time resolved photoluminescence studies were carried out. It was observed that it is a rare breed of phosphor material that exhibits exceptional luminescence properties such as the capability to give high emission output till 5.0 mol% without undergoing quenching and unique property to get excited by mid ultraviolet (MUV) light, near ultraviolet (NUV) light, as well as by visible light such as blue and green. It was also observed that energy transfer primarily takes place from tungstate group of host to Eu3+. In fact energy transfer from the host to Eu3+ becomes more and more efficient with the increasing concentration of Eu3+ ions. Two lifetime values are observed for all europium ion (Eu3+) concentrations, one of the order of 465–650 μs (TS, short lifetime) and the other of the order of 1050–1320 ms (TL, longer lifetime). This reflects the fact that Eu3+ ions occupy two sites; regular symmetric Ba2+ site (S1) and asymmetric site (S2), which will be closer to charge compensating defects. Calculation of Judd–Ofelt parameter illustrated that at all europium concentrations, the local surrounding around it lacked inversion symmetry (asymmetric environment), and the exact point group symmetry around europium ion was found to be C6v. The red purity (intense 5D0–7F2) and high quantum efficiency (78%) of BaWO4:Eu3+ projects it as a new red phosphor for application in white light emitting diodes.

Energy transfer dynamics and time resolved photoluminescence in BaWO4:Eu3+ nanophosphors synthesized by mechanical activation

One-dimensional α-MoO3 nanofibers of 280–320 nm diameters were synthesized by a hydrothermal method. The morphologies and compositions of as-synthesized α-MoO3 nanofibers have been characterized by X-ray powder diffraction, Raman spectroscopy, and field-emission scanning electron microscopy. X-ray photoelectron spectroscopy showed the predominantly 6+ oxidation state with a small percentage of reduced δ+ (5 < δ < 6) oxidation state. The field-emission properties of α-MoO3 nanofibers show a lower turn-on electric field of 2.48 V μm and threshold electric field of 3.10 V μm. The results suggest that the α-MoO3 nanofibers are promising candidate for efficient and highperformance field-emission devices. Copyright © 2018 VBRI Press.

Synthesis of α-MoO3 nanofibers for enhanced field-emission properties

We present the structural investigation on multiferroic Ba1-xSrxMnO3 perovskite manganites with x = 0.50, 0.60, 0.70 and 0.75 synthesized by combustion method. Rietveld refinement of powder X-ray diffraction data reveals the hexagonal structure with space group P63/mmc for all compositions. The unit cell lattice parameters for Ba1-xSrxMnO3 decrease monotonically with Sr-substitution on Ba-site. The value of structural tolerance factor decreases from 1.047 for x = 0.50 to 1.018 for x = 0.75.

Synthesis and structural investigations on multiferroic Ba1-xSrxMnO3 perovskite manganites

We have investigated the effect of sintering temperature on the densification behaviour, grain size, structural and dielectric properties of BaTiO3 ceramics, prepared by high energy ball milling method. The Powder x-ray diffraction reveals the tetragonal structure with space group P4mm for all the samples. The samples were sintered at four different temperatures, (T = 900°C, 1000°C, 1100°C, 1200°C and 1300°C). Density increased with increasing sintering temperature, reaching up to 97% at 1300°C. A grain growth was observed with increasing sintering temperature. Impedance analyses of the sintered samples at various temperatures were performed. Increase in dielectric constant and Curie temperature is observed with increasing sintering temperature.

Effect of grain size on structural and dielectric properties of barium titanate piezoceramics synthesized by high energy ball milling

In this work, we report the effects of calcination temperature on structural, dielectric, semiconducting and optical properties of YFeO3 nanoparticles prepared by a high energy ball milling process. The structural analysis of the X-ray diffraction data shows that YFeO3 exists in orthorhombic as well as in hexagonal mixed-phase states. The Rietveld analysis confirms that orthorhombic YFeO3 crystallizes into Pnma space group. The optical band gap of YFeO3 reduces from 1.96 eV to 1.68 eV with increasing the calcination temperature of the YFeO3 sample. The bandgap reducing effect might be attributed to the increased crystallite size and decreased lattice strain which is confirmed by the Williamson-Hall plot method. The obtained low bandgap YFeO3 ceramic may provide a new possibility to develop eco-friendly Ferroelectric photovoltaic devices.

Narendra Kumar Verma

Papers

Energy transfer dynamics and time resolved photoluminescence in BaWO4:Eu3+ nanophosphors synthesized by mechanical activation

Synthesis of α-MoO3 nanofibers for enhanced field-emission properties

Synthesis and structural investigations on multiferroic Ba1-xSrxMnO3 perovskite manganites

Effect of grain size on structural and dielectric properties of barium titanate piezoceramics synthesized by high energy ball milling

Structural, Dielectric, Semiconducting and optical properties of High-Energy Ball Milled YFeO3 Nano-particles