Mukut Gohain

Influence of ultrasonication times on the tunable colour emission of ZnO nanophosphors for lighting applications.

This paper reports on the sonochemical synthesis of zinc oxide (ZnO) nanophosphors (NPr) at different ultrasonication times (5 min, 30 min, 1h, 5h, 10h and 15 h) for near white light emission applications. X-ray photoelectron spectroscopy indicated that the O1s peak consists of two components. These were O1 (ZnO) and O2 (deficient oxygen; OH groups) centred at 529.7±0.3 eV and 531.1±0.3 eV, respectively. All samples showed UV and defect level emission (DLE). The DLE enhancement was due to the increase in oxygen related defects such as oxygen vacancies/interstitials. Due to the combination of near UV and DLE near white light emission in ZnO NPr was obtained. The emission could be tuned with different ultrasonic times. It was found that the ultrasonication time influenced the growth mechanism and luminescence properties of the ZnO NPr.

Dopant distribution and influence of sonication temperature on the pure red light emission of mixed oxide phosphor for solid state lighting

In this study, europium doped yttrium gadolinium (Y1.4Gd0.5Eu0.1O3) mixed oxide phosphors were synthesized by a sonochemical method at different growth temperatures (50°C, 100°C, 150°C and 200°C) for pure red light emission applications. The compositional identification, presence of dopants and the distribution of doping materials in the crystal lattice was studied by TOF-SIMS. The formation and growth mechanisms in the sonochemical synthesis of Y1.4Gd0.5Eu0.1O3 nanophosphors are discussed in detail. Different spectral and Judd-Ofelt parameters were estimated from photoluminescence data. Optical gain and efficiency parameters were calculated with the variation of synthesis environment and an efficient synthesis method to make good red emitting phosphors for solid-state lighting and display applications were proposed.

Nano CuFe2O4: an efficient, magnetically separable catalyst for transesterification of β-ketoesters

The preparation of a variety of β-ketoesters was achieved in high yields from methyl acetoacetate under neutral conditions through the utilization of magnetic CuFe2O4 nanoparticles as catalyst. Recycling of the catalyst was performed up to eight times without significant loss in activity. The catalyst was characterized using XRD, XPS, SEM and TEM techniques.

The role of neutral and ionized oxygen defects in the emission of tin oxide nanocrystals for near white light application

Tin oxide (SnO2) nanocrystals (NCs) based phosphor was synthesized by a green chemistry microwave-assisted hydrothermal method at different reactor pressures. The x-ray diffraction analysis showed that a single rutile SnO2 phase with a tetragonal lattice structure was formed. The photoluminescence emission was measured for He-Cd laser excitation at 325 nm and it showed a broad band emission from 400 to 800 nm for all the synthesized reactor pressures. The broad emission spectra were due to the creation of various oxygen and tin defects as confirmed by x-ray photoelectron spectroscopy data. The origin of the emission in the SnO2 NCs is discussed with the help of an energy band diagram. Analysis suggests that the visible emission of SnO2 NCs is due to a transition of an electron from a level close to the conduction band edge to a deeply trapped hole in the SnO2 NCs. The NCs were found to be suitable for warm near white light emission device applications.

Al(OTf)3 Catalysed Friedel-Crafts Michael Type Addition of Indoles to α,β-Unsaturated Ketones with PEG-200 as Recyclable Solvent

An Al(OTf)3 catalysed efficient Friedel–Crafts Michael type addition of indoles to α,β-unsaturated ketones using recyclable PEG-200 as an alternative reaction solvent is disclosed. The reaction under microwave irradiation is clean, leads to excellent yields in minutes and reduces the use of volatile organic compounds.

Crystal structure of 2,3-dicyano-1,4-phenylene bis(trifluoromethanesulfonate), C10H2F6N2O6S2

C10H2F6N2O6S2, orthorhombic, P212121 (no. 19), a = 8.1480(10) Å, b = 11.5550(15) Å, c = 16.178(2) Å, V = 1523.2 Å, Z = 4, Rgt(F) = 0.0390, wRref(F ) = 0.1081, T = 300 K.

2,5-Dihexyl­thio­phene 1,1-dioxide

In the title molecule, C16H28O2S, the two n-hexyl groups are in all-trans conformations. Their C atoms are situated close to the plane of the thiophene ring with a maximum deviation of 0.718 (6) Å for one of the terminal methyl groups. In the crystal, a short C—H⋯O contact is observed between thiophene 1,1-dioxide groups.

4-(2-Bromo-phen-yl)-2-phenyl-pyrano[3,2-c]chromen-5(4H)-one.

In the title compound, C24H15BrO3, the pyranochromenone ring is essentially planar, while the 2-bromophenyl group is almost perpendicular to it [85.58 (6)°]. In the crystal, inversion dimers linked by pairs of weak C—H⋯π bonds occur; there is also a short interatomic contact found between the Br and carbonyl O atoms [3.016 (1) Å].

5-(3,4-Dimeth­oxy­benzyl­idene)-1,3-dimethyl-1,3-diazinane-2,4,6-trione

In the title compound, C15H16N2O5, the dihedral angle between 1,3-diazinane and benzene rings is only 4.27 (1)°. The essentially planar molecular structure is characterized by a short intramolecular C—H⋯O separation and by an exceptionally large bond angle of 138.25 (14)° at the bridging methine C atom. The methoxy groups deviate somewhat from the plane of the benzene ring, with C—C—O—C torsion angles of −15.6 (1) and 9.17 (6)°. In the crystal, molecules form centrosymmetric dimers via donor–acceptor π–π interactions, with a centroid–centroid distance of 3.401 (1) Å.

Racemic tricarbon­yl[7-meth­oxy-2-(η6-phen­yl)chromane]­chromium(0)

In the title compound, [Cr(C16H16O2)(CO)3], the Cr0 atom of the Cr(CO)3 unit is coordinated to the phenyl ring of the flavan ligand in an η6 mode, with a normal arene-to-metal distance. The Cr(CO)3 unit exhibits a three-legged piano-stool conformation, while the dihydropyran ring displays a distorted envelope configuration. The phenyl ring is twisted away from the fused ring system by 25.5 (2)°. The methoxy group is almost coplanar with the phenyl ring [CMe—O—Car—Car torsion angle = 8.46 (2)°]. The crystal packing is stabilized by intermolecular C—H⋯O interactions.