Structural and Photoluminescence Characterization of Oxyfluorides for Phosphor Applications

Structural changes and self-activated photoluminescence in reductively annealed Sr3AlO4F

Structural distortions and self-activated photoluminescence in reductively annealed Ba2SrGaO4F

Bright and Blue Nanocrystal Emitters

Direct evidence for B-B contact in amorphous Ni 2B from high-resolution neutron diffraction

Synthesis and characterization of nano Sr2CeO4 doped with Eu and Gd phosphor

A series of single-phase LiBaBO3:Ce3+, AR (R = Eu2+, Mn2+, Dy3+, Sm3+, Tb3+) and LiBaBO3:Tb3+, BE (E = Mn2+, Dy3+, Sm3+) phosphors were prepared via a high-temperature solid-state method. The structure and luminescence properties of the phosphors are described. The optical property and energy transfer mechanism between Ce3+/Tb3+ and the rare earth (RE) ions or transition metal ion (Mn2+) are investigated in detail. The energy transfer, from Ce3+ to other ions, is attributed to the dipole–dipole interaction. The separation of the excitation spectrum and the quenching of 5D3 within Tb3+ can be influenced by the ions. More importantly, tunable emission colors are obtained from deep pink to yellow when ions were co-doped with Ce3+/Tb3+ during their sensitization in LiBaBO3, indicating LiBaBO3 may be a potential phosphor in LED (Light-emitting diode) application.

A new high-resolution diffraction method is introduced without the confinement of using a highly collimated beam, necessary in conventional high-resolution diffraction. Larmor precession of a polarised neutron beam is used to label each neutron of the incident and scattered neutron beam with its wavelength and scattering angle. Giving the Larmor precession device front and back faces inclined over an angle adjusted to the scattering angle used, the wavelength–transmission angle relation of the Larmor precession matches precisely with the wavelength–scattering angle relation of the scattering vector. In this way the Larmor precession phases of different momentum transfers and thus the scattering vectors, can be measured with extremely high resolution. It should be possible to measure lattice constants with relative accuracy of better than 10−5, while using a low resolution beam, which means an effective intensity gain of orders of magnitude. Applications of this method are discussed.

Luminescence Characteristics of Eu and Tb Doped YGdBO3 Phosphor

Use of compact fluorescent lamps (CFL) is on the increase for photovoltaic lighting systems due to their high luminous efficacy and ability to provide adequate lumen output for a given lighting application. The luminous efficacy increases with switching frequency while providing eye comfort to the user. The low electrical consumption makes the CFL an ideal choice for photovoltaic power systems for lighting applications. However the CFL's electrical requirements are not easily met by hard switched inverters due to their higher switching losses at higher frequencies and the difficulty in meeting the complex electrical requirements of CFL of preheat and ignition voltage, resulting in lower efficiency. A series parallel resonant mode sine wave inverter is discussed which provides the basic electrical characteristics requirements of CFL, protection needs for higher reliability while offering higher inverter efficiency and above all a fairly constant lumen output throughout the operating DC voltage range by a unique control scheme. A series interrupting-type charge controller makes the PV power system self-sufficient for producing light in remote areas while maintaining reliability.

We have investigated LaCo0.5Mn0.5O3+ δ compounds with different oxygen content by means of magnetization, high resolution and small-angle neutron diffraction measurements. Oxygen content decrease down to stoichiometric composition leads to an essential increase of TC and magnetic moment while Co/Mn ionic ordering degree is kept almost constant. It is assumed that upon oxygen reduction Co3+ ions change their valence state down to 2+ one that leads to dominating of Co2+-Mn4+ ferromagnetic interactions as well as TC increase. Magnetic properties can be explained in terms of coexistence of long-range ferromagnetic order and short-range clusters with antiferromagnetic interactions prevailing. Size distribution of the mentioned short-range magnetic inhomogeneities is rather mild within the samples but it is strongly temperature dependent.

Precise lattice strains measured using high-resolution neutron diffraction from a solid polycrystalline sample are used to explore the single-crystal elastic constants of α-Al2O3(corundum). The analysis confirms a recent suggestion that, contrary to the long-accepted view, the sign ofs14should be negative. It also indicates that the magnitude ofs13should be adjusted from −0.38 × 10−12to −0.47 × 10−12 Pa−1. It is found that, micromechanically, the polycrystal responds to stress in a manner very close to the Reuss limit. The results confirm the applicability of the diffraction method, which could prove useful when other techniques give ambiguous results.

Copper(I)-Based Highly Emissive All-Inorganic Rare-Earth Halide Clusters

Mn2+ doped (0–50.0 molar %) ZnS d-dots have been synthesized in water medium by using an environment friendly low cost chemical technique. Tunable dual emission in UV and yellow-orange regions is achieved by tailoring the Mn2+ doping concentration in the host ZnS nanocrystal. The optimum doping concentration for achieving efficient photoluminescence (PL) emission is determined to be ∼1.10 (at. %) corresponding to 40.0 (molar %) of Mn2+ doping concentration used during synthesis. The mechanism of charge transfer from the host to the dopant leading to the intensity modulated tunable (594-610 nm) yellow-orange PL emission is straightforwardly understood as no capping agent is used. The temperature dependent PL emission measurements are carried out, viz., in 1.10 at. % Mn2+ doped sample and the experimental results are explained by using a theoretical PL emission model. It is found that the ratio of non-radiative to radiative recombination rates is temperature dependent and this phenomenon has not been reported, so far, in Mn2+ doped ZnS system. The colour tuning of the emitted light from the samples are evident from the calculated chromaticity coordinates. UV light irradiation for 150 min in 40.0 (molar %) Mn2+ doped sample shows an enhancement of 33% in PL emission intensity.

The conversion of epoxy to carbonyl group in graphene oxide (GO) thin films has been carried out via oxygen plasma treatment, and the effects of this conversion on structural and optical properties were investigated. Hydrophilicity of the prepared GO solution allows it to be uniformly deposited onto substrates in the form of thin films. High-resolution transmission electron microscopy and electron diffraction analysis confirmed 4–5 layers of the graphene oxide layers which are polycrystalline in structure, and the oxygen plasma treatment results in short-range order crystallization in graphene oxide films with an increase in interplanar spacing which can be attributed to the presence of oxygen functional groups on the graphene oxide layers. Electron energy loss spectroscopy (EELS) and Raman spectroscopy confirm the presence of the sp2 and sp3 hybridization due to the disordered crystal structures of the carbon atoms results from oxidation, and XPS analysis shows that epoxy pairs convert to more stable C═O and O–C═O groups with oxygen plasma treatment. The broad energy level distribution resulting from the broad size distribution of the sp2 clusters produces excitation-dependent photoluminescent (PL) emission in a broad wavelength range from 400 to 650 nm. Our results suggest that as oxygen pressure increases, there is a change from epoxide to carbonyl linkages which also resulted in variation in PL emission.

The luminescent properties of Ce3+, Eu2+, Ce3+-Tb3+, and Eu3+ in the mullite (Al6Si2O13) host were investigated for realization of full colors phosphors with a single type host. Ce3+ and Eu2+ in mullite showed blue photoluminescence (PL), whereas green and red emission were obtained in the Ce3+-Tb3+ and Eu3+ doped mullite. The prepared phosphors had the excitation band around 300 nm. The PL intensity at 200 °C kept 70 % of the initial intensity at room temperature.The X-ray diffraction study indicated the incorporation of the rare-earth (RE) ions in the mullite lattice without forming secondary phases, although it was not probable that the RE ions substituted for Al3+ and Si4+ because of the significant difference in ionic size. The bond-valence-sum and the differential electron density map analysis indicated that the doped RE ions occupied the stoichiometrically-introduced vacant oxygen site, which was the site for oxygen originally. The amphoteric nature of the oxygen site in mullite was proposed.