CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

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small value, thereby giving rise to sharp NMR peaks. Thus, the MAS NMR technique simplifies the solid-state NMR patterns and individual chemical environments can be correlated with corresponding chemical shift values obtained from these samples [125, 126]. Although, MAS is an efficient technique employed for getting high resolution NMR patterns from solid samples, in many cases, due to spinning, side bands, which are mirror images of the isotropic peak and spread from the isotropic peak by integer multiples of the spinning frequency, appear along with the central isotropic peak for nuclei having wide range of chemical shift values. For nuclei having a nuclear spin value ½, sideband pattern is a measure of the chemical shift anisotropy and valuable information regarding the symmetry of the electronic environment around a probe nuclei can be obtained from the intensity distribution of sidebands. However, in the presence of large number of isotropic peaks, the number of sidebands also increases, and there can be overlap between the sidebands and isotropic peaks, which makes the MAS NMR pattern complicated. In the present study, 31 P MAS NMR patterns were recorded using a 500 MHz Bruker Avance machine with a 31 P basic frequency of 202.4 MHz. The samples were packed inside 2.5 mm rotors and subjected to various spinning speeds ranging between 5000 to 10000 Hz. The chemical shift values are expressed with respect to 85% H 3 PO 4 solution. The typical 90° pulse duration and relaxation delay are 4 μs and 5s, respectively. 2.7.6. Photoluminescence spectroscopy: Photoluminescence (PL) is a process, in which a substance absorbs photons (electromagnetic radiation) and then re-radiates photons. Quantum mechanically, this can be described as an excitation to a higher energy state by absorption of photon and then a return to a lower energy state accompanied by the emission of a photon. The schematic representation of spectrofluorimeter can be seen in Fig.17. The light from an excitation source passes through a monochromator, and strikes the sample. A proportion of the incident light is absorbed by the sample, and some of the molecules in the 50
sample fluoresce. The fluorescent light is emitted in all directions. Some of this fluorescent light passes through a second monochromator and reaches a detector, which is usually placed at 90° to the incident light beam to minimize the risk of transmitted or reflected incident light reaching the detector. Various light sources may be used as excitation sources, including lasers, photodiodes and lamps (xenon arcs and mercury-vapor lamps). Fig.17. Schematic representation of spectrofluorimeter. Xenon arc lamp has a continuous emission spectrum with nearly constant intensity in the range from 300-800 nm and a sufficient irradiance for measurements down to 200 nm. A monochromator transmits light of an adjustable wavelength with an adjustable tolerance. The most common type of monochromator utilizes a diffraction grating wherein a collimated light illuminates a grating and exits with a different angle depending on the wavelength. The monochromator can then be adjusted to select which wavelengths to transmit. The most comonly used detector is photomultiflier tube (PMT). Excitation and Emission spectra: The spectrofluorometer with dual monochromators and a continuous excitation light source can record both excitation spectrum and emission 51
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SYNTHESIS AND CHARACTERIZATION OF L
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STATEMENT BY AUTHOR This dissertati
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Dedicated to ……… My beloved b
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also thankful to all the members of
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2.3 Synthesis of binary oxide nanom
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CHAPTER 5: Zinc Gallate ...........
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imaging, scintillators, lasers, etc
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morphology by heating at 500 and 90
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nanoparticles having hexagonal stru
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100°C and 185°C, respectively in
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into poly methyl methacryllate (PMM
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3. N. M. Dimitrijevic, Z. V. Saponj
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Fig.13: Fig.14: (a) Simplified ray
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Eu 3+ ions after heat treatment at
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615 nm Fig.50: FT-IR patterns (a) a
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area electron diffraction pattern a
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different amounts of Eu 3+ . Fig.86
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and 545 nm, respectively. Fig.106:
Page 37 and 38: List of Tables: Table 1: Variation
Page 39 and 40: CHAPTER 1: Introduction 1.1 Histori
Page 41 and 42: Rods, cylinders, wires and tubes ar
Page 43 and 44: must be supersaturated either by di
Page 45 and 46: - + - + charge stabilized nanoparti
Page 47 and 48: exothermic reaction between the met
Page 49 and 50: constant, ħ is h/2π, e is the ele
Page 51 and 52: these platinum complexes have been
Page 53 and 54: (IR), visible and ultra-violet (UV)
Page 55 and 56: in Ce 3+ , Pr 3+ , Tb 3+ and CT abs
Page 57 and 58: assisted by lattice phonons of appr
Page 59 and 60: decay-time reduction is much easier
Page 61 and 62: nanocrystals is shown in Fig.10 [58
Page 63 and 64: depends strongly on the nature of t
Page 65 and 66: corresponding emission and excitati
Page 67 and 68: doped nanomaterials of the above me
Page 69 and 70: will be formed and subsequently it
Page 71 and 72: Eu 3+ ions were also subjected to s
Page 73 and 74: transferred into a two-necked RB fl
Page 75 and 76: Where λ is the wavelength of X-ray
Page 77 and 78: Micro-structural characterization b
Page 79 and 80: electrons (i.e. diffraction mode).
Page 81 and 82: diffraction spots. By tilting a cry
Page 83 and 84: surface. The contact mode can obtai
Page 85 and 86: three types lines in the scattered
Page 87: solids tend to be broadened because
Page 91 and 92: pulse frequency) as excitation sour
Page 93 and 94: Lanthanide ions doped Ga 2 O 3 nano
Page 95 and 96: atoms at three corners and the lone
Page 97 and 98: Figure 19 (a-d) shows SEM images of
Page 99 and 100: Based on these results, it can be i
Page 101 and 102: almost normal to the equatorial pla
Page 103 and 104: Table 2. Summary of important modes
Page 105 and 106: systematic disappearance of these t
Page 107 and 108: comparison, Eu 3+ ions alone in wat
Page 109 and 110: the samples, suggesting that Eu 3+
Page 111 and 112: These inferences are further substa
Page 113 and 114: Similar DTA peaks have been reporte
Page 115 and 116: GaOOH samples doped with different
Page 117 and 118: The cell parameters increases with
Page 119 and 120: strong emission compared to corresp
Page 121 and 122: curves are shown in Fig.39. Lifetim
Page 123 and 124: Similar results are also observed f
Page 125 and 126: intensity of XRD peaks correspond t
Page 127 and 128: compared to the bulk material and a
Page 129 and 130: is almost 1½ times that of peak B1
Page 131 and 132: 3.8 Interaction of Eu 3+ ions with
Page 133 and 134: The spectrum shows strong emission
Page 135 and 136: The decay curves are found to be bi
Page 137 and 138: As prepared undoped Sb 2 O 3 sample
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Intensity(arb.units) 1.0 0.8 0.6 0.
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3+ having surface lanthanide ions.
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diffraction patterns from the GaPO
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5 D 0 7 F 2 level to 7 F 7 7 1 , F
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The second possibility is the excha
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chemical shift anisotropy is much h
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not have strong interaction with th
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(001) (110) (011) (101) (020) (101)
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growth centre compared to higher vi
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observed after excitation at 250 an
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3+ 3+ concentration quenching. Tb l
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Compared to the selected area elect
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lattice. Lanthanide ions occupying
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obtained after 275 nm excitation is
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The luminescence dynamics associate
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that the broad peak can be resolved
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espectively. Value of this integral
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ethylene glycol moiety (stabilizing
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Room temperature and 100°C synthes
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heavier metal ion as compared to La
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Similar studies were also carried o
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3+ 3+ faster decay component is ass
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the other hand the Eu 3+ lifetime h
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3+ 4.4.8 Luminescence studies on Sm
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CHAPTER 5: Zinc gallate (ZnGa 2 O 4
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In pure EG an amorphous product is
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water content in the reaction mediu
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nucleation, thereby leading to incr
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particles. Thus the TEM studies als
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value. The lattice parameters calcu
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Quantum yield of the blue emission
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5.5.2. Eu 3+ doped ZnGa 1.5 In 0.5
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CHAPTER 6: Tungstates [MWO 4 (M = C
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ionic radius of the metal cation ca
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lattice. Asymmetric ratio is ~ 12 f
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700 Intensity (arb.units) 600 λ ex
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Intensity (arb.units) 25000 20000 1
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Strong green emission has been obse
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consists of strong band at 255 nm a
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peak can be attributed to the cryst
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nm) is observed from Er 3+ doped Ga
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and Dy 3+ doped CaWO 4 nanoparticle
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REFERENCES 1. D. J. Barber, I. C. F
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32. K. A. Gschneidner, Jr., L. Eyri
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65. Z. Deng, F. Tang, D. Chen, X. M
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100. A. Rouanel, J. J. Serra, K. Al
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130. F. Li, W. Jianhuai, L. Jiongti
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166. L. Fu, Z. Liu, Y. Liu, B. Han,
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205. R. Sasikala, V. Sudarsan, C. S
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238. E. Oldfield, R. A. Kinsey, K.
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271. B. G. Hyde, S. Andersson, ”I
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B. S. Naidu, B. Vishwanadh, V. Suda
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9. Room temperature synthesis of mu
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