CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

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understood, but these peaks have also been observed in the GaOOH nanorods [185]. The disappearance of peaks at 385 and 525 cm -1 , together with reduced intensity of other peaks, clearly indicate that Eu 3+ incorporation results in the disruption of basic building blocks of GaOOH phase. When the later is compared with amorphous Ga(OH) 3 sample, similar features are observed in Ga(OH) 3 sample too, indicating that the crystal structure is being disrupted with Eu 3+ addition and finally with more than 1 at. % Eu 3+ it is completely disrupted. This is further evident by new peaks appearing at ~ 1490 and 1635 cm -1 for GaOOH containing higher Eu 3+ concentrations (Fig.23 (A)). Based on the previous IR studies of rare earth hydroxides like La(OH) 3 [188] and the pattern corresponding to Ga(OH) 3 shown in Fig.23A(f), the peaks at 1490 and 1635 cm -1 have been attributed to the bending vibrations of the OH groups associated with Eu(OH) 3 and Ga(OH) 3 phases respectively. Another peak at 1383 cm -1 which is present in the FT-IR patterns of all the samples is arising due to adsorbed carbonate species [56, 189] formed during sample preparation. The structure of GaOOH being affected by Eu 3+ incorporation is also seen in the high frequency region ~ 3500-2600 cm -1 . This may be considered as the overlapping of peaks around 3400, 3250 and 2975 cm -1 (Fig.23B). From the previous vibrational studies [56, 182, 190-194] on GaOOH and AlOOH (which has the structure similar to GaOOH), the peak around 3400 cm -1 can be attributed to the OH stretching vibrations of physisorbed H 2 O molecules, while that 2975 and 3250 cm -1 may be attributed to the two different kinds of OH bonds associated with its structure. As discussed earlier, in the basic building unit of GaOOH, the two non-equivalent oxygen atoms in the GaO 6 octahedron are bound differently to the adjacent hydrogen atoms. One of the oxygen atoms is bound directly to hydrogen, while the other one is bound via the hydrogen bonding, making differences in their bond strengths. The peak at ~ 2975 cm -1 is attributed to the stretching vibrations of the OH groups which are hydrogen bonded to GaO 6 octahedra, while the peak at ~ 3250 cm -1 is due to non-hydrogen bonded OH linkages. The 66
systematic disappearance of these two absorptions in the Eu 3+ containing GaOOH sample, indicate that Eu 3+ is in fact affecting the lattice structure through the OH linkages. An attempt was made to understand structural changes taking place in the GaOOH lattice with Eu 3+ incorporation. At this stage, it is necessary to understand how the GaOOH phase is being formed and how interactions with lanthanide ions affect different types of linkages in GaOOH lattice. Under alkaline conditions GaOOH is thought to be formed from Ga(OH) 4 - species generated in solution (equation 19) [143]. This Ga(OH) 4 - on thermal decomposition at ~100°C leads to the formation of GaOOH. ~100 ( ) ( ) ( ) ( S) ( aq) 3+ OH OH C Ga − Ga OH − Ga OH − ° − ⎯⎯⎯→ ⎯⎯⎯→ ⎯⎯⎯→ GaOOH + OH + H 3 4 aq 2O ... (19) A schematic representation of a fragment of GaOOH lattice, depicting GaO 6 octahedra, O tetrahedra and H atoms attached with oxygen atoms, obtained by the simulation program MOLDRAW [195] is shown in Fig.24. The unit cell is shown within the rectangle drawn with light black line. Hydrogen bonds existing between the layers stabilize the layered structure of GaOOH. When lanthanide ions like Eu 3+ are present in the reaction medium, due to the higher solubility product of lanthanide hydroxides (Ln(OH) 3 ) compared to Ga(OH) 3 [196], the Ga(OH) 3 is formed initially and this later reacts with OH - in the reaction medium to form Ga(OH) 4 ⎯. As concentration of Eu 3+ ions are much smaller compared to Ga 3+ , it is quite possible that each Eu 3+ ion will have number of Ga(OH) 4 ⎯ species in their vicinity. For the purpose of charge neutrality minimum of three anionic species (Ga(OH) 4 ⎯) must be surrounding the Eu 3+ ions. On decomposition of Eu 3+ -3Ga(OH) 4 ⎯ species to GaOOH:Eu at ~100°C, Eu 3+ ions can either migrate to Ga 3+ site in the GaOOH lattice or it can occupy the space between the layers of GaOOH. Due to smaller ionic radius of Eu 3+ compared to inter layer spacing of GaOOH (~ 2.5 Å) [197], Eu 3+ ions/ species have a tendency to get incorporated at the inter-layers of GaOOH wherein it can preferentially interact with OH groups to form europium hydroxide species. Formation of such hydroxide species 67
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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:
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List of Tables: Table 1: Variation
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CHAPTER 1: Introduction 1.1 Histori
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Rods, cylinders, wires and tubes ar
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must be supersaturated either by di
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- + - + charge stabilized nanoparti
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exothermic reaction between the met
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constant, ħ is h/2π, e is the ele
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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 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: Table 2. Summary of important modes
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
Page 139 and 140: Intensity(arb.units) 1.0 0.8 0.6 0.
Page 141 and 142: 3+ having surface lanthanide ions.
Page 143 and 144: diffraction patterns from the GaPO
Page 145 and 146: 5 D 0 7 F 2 level to 7 F 7 7 1 , F
Page 147 and 148: The second possibility is the excha
Page 149 and 150: chemical shift anisotropy is much h
Page 151 and 152: not have strong interaction with th
Page 153 and 154: (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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