CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

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the surface of the sample while the tip movements normal to the surface are measured. The deflections occurred in the tip, due to the interaction forces between the tip and sample surface, can be measured by focussing a laser beam onto cantilever and detecting the reflected light from the cantilever using a position sensitive detector. Schematic diagram of atomic force imaging is shown in Fig 15 (a). As the tip is rastered over the surface, a feedback mechanism is employed to ensure that the piezo-electric motors maintain a constant tip force or height above the sample surface. The tip movements normal to the surface are digitally recorded and can be processed and displayed in three-dimensions by a computer. This technique has a lateral resolution of 1 to 5 nm. AFM is typically used to obtain a threedimensional surface image or to determine the surface roughness of thin films and crystal grains. There are mainly two types of AFM modes, namely the contact mode and the semi contact/taping mode, which are used for imaging the samples. The schematic representation of the different types forces acting between tip and sample in the two methods of imaging is shown in Fig.15 (b) and are described below. Tip cantilever (a) (b) Fig.15. (a) Principle of AFM imaging, (b) variation of interaction force versus distance between the AFM tip and substrate. (1) Contact mode: Here, the force between the probe tip and substrate is repulsive, and it is within the range of 10 -8 to 10 -7 N. The force is set by pushing a cantilever against the sample 44
surface. The contact mode can obtain a higher atomic resolution than the other modes, but it may damage a soft material due to excessive tracking forces applied from the probe on the sample. Unlike the other modes, frictional and adhesive forces will affect the image. (2) Non-contact/tapping mode: Here, the main interaction force between the probe tip and the substrate is attractive due to van der Waals force and it is in the range of 10 -10 to 10 -12 N. In this mode, cantilever oscillates in the attractive region and its oscillation frequency gets modulated depending on the sample surface features. The tip is 5 to 150 nm above the sample surface. The resolution in this mode is limited by the interactions with the surrounding environment. In the present study, Atomic force microscopic (AFM) measurements were performed in contact mode using an AFM instrument from Ms. NT-MDT (solver model) with a 50 µm scanner head. Samples were dispersed in methanol and a drop of this solution was added on highly oriented pyrolytic graphite (HOPG)/ mica sheets. These samples are dried properly before loading in AFM. 2.7.4. Vibrational spectroscopy: Vibrational spectroscopic techniques are extensively used to identify the nature of different linkages present in a material. These methods also give valuable information regarding the symmetry of different vibrational units. Two types of vibrational techniques, namely IR and Raman spectroscopy are used in the present study and the principle is briefly described below. IR spectroscopy: Vibrations of bonds and groups which involve a change in the dipole moment results in the absorption of infrared radiation which forms the basis of IR spectroscopy. Modern IR instruments are based on Fourier transformation method to improve the signal to noise ratio. Unlike conventional IR instrument, in FTIR instrument, all the frequencies are used simultaneously to excite all the vibrational modes of different types of bonds/linkages present in the sample. This reduces the experimental time considerably. 45
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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
Page 31 and 32: area electron diffraction pattern a
Page 33 and 34: different amounts of Eu 3+ . Fig.86
Page 35 and 36: 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: diffraction spots. By tilting a cry
Page 85 and 86: three types lines in the scattered
Page 87 and 88: solids tend to be broadened because
Page 89 and 90: sample fluoresce. The fluorescent l
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
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The spectrum shows strong emission
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The decay curves are found to be bi
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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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