CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

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CHAPTER 4: Phosphates 3+ 3+ 3+ 4.1. Introduction: Phosphates of Ga , Sb and Bi are of interest because of their potential technological applications [212-220]. For example, GaPO 4 is a good piezo-electric material whereas SbPO and BiPO 4 4 are used as catalysts as well as in optical/ photonic devices [221- 225]. Doping lanthanide ions in such phosphates is an attractive option for making materials with multi functional applications. Under ambient conditions, GaPO 4 exists in hexagonal form whereas SbPO 4 and BiPO 4 adopt a monoclinic structure. BiPO4 is also known to exist in hexagonal form [226, 227]. Unlike this, LnPO 4 (Ln = lanthanide) exist mainly in two crystalline modifications, viz. monazite and xenotime [228]. Monazite structure is adopted by 3+ 3+ lanthanide phosphates with relatively larger lanthanide ions (i.e., La - Gd ) while xenotime structure is formed by smaller lanthanide ions (i.e., Tb 3+ -Lu 3+ ). Essential difference in both the structures is that in the xenotime structure, Ln 3+ ions exist as regular LnO 8 polyhedra whereas in the monazite structure, lanthanide ions (Ln 3+ ) exist as LnO 9 polyhedra [228]. For making lanthanide ions based luminescent materials using phosphate hosts like GaPO 4 , SbPO and BiPO 4 4, it will be ideal if solid solution formation between these phosphates and lanthanide phosphates exist. The major problem with the solid solution formation in this system is the large difference in the ionic radii of the cations and difference in their 3+ 3+ coordination numbers, particularly for Ga and Sb ions in GaPO 4 and SbPO4 respectively. Further, the solubility product values are significantly different for GaPO (10 -21 - 4 ), BiPO 4 (10 23 ) and LnPO 4 (~ 10 -26 to 10 -25 ) [229-231] which prevent the formation of solid solution between these compounds through co-precipitation techniques. However, if the metal phosphate nanoparticles are prepared under alkaline conditions in aqueous or alcoholic solutions, the surface hydroxyl groups on nanoparticles may undergo ion exchange with lanthanide ions. Such an ion exchange process will lead to the formation of nanoparticles 102
3+ having surface lanthanide ions. This is particularly valid for GaPO 4, as the Ga ionic radius is much smaller as compared to lanthanide ions, besides significant difference in the coordination numbers around the cations. Situation is slightly different for SbPO 4 nanomaterials as the ionic radius of Sb 3+ (0.76Å) [177] is expected to be comparable with that of lanthanide ions with coordination number four, although lanthanide ions with such low coordination are not commonly observed. In contrast to this, Bi 3+ ions in BiPO 4 have comparable ionic size to that of lanthanide ions and crystal structure of BiPO 4 is similar to that of lanthanide phosphates, there by facilitating the improved solubility of lanthanide ions in BiPO . 4 3+ 3+ 3+ 3+ In the present study Eu , Ce , Tb , Dy , Sm 3+ ions were chosen for doping in the above mentioned hosts. The luminescence characteristics of Eu 3+ with respect to different environments are well understood and hence can be used as a probe to monitor the structural 3+ 3+ changes taking place with a host lattice. The ions Ce and Tb are known to have strong absorption in the UV region with Tb 3+ ions emitting strongly in the visible region. In addition Ce 3+ 3+ 3+ is an efficient sensitizer to Tb (due to energy transfer from Ce to Tb 3+ ions) and 3+ 3+ therefore materials doped with Ce and Tb have been developed to generate efficient 3+ 3+ green light for display applications. This energy transfer between Ce and Tb ions is very sensitive to the crystal structure of the host, surface modification, etc. [112, 113, 232]. For example in CePO 4 :Tb 3+ and CePO :Dy 3+ 4 nanomaterials strong energy transfer has been observed from Ce 3+ 3+ 3+ 3+ 3+ to Tb or Dy ions. However, in Ce co-doped YAG:Tb 3+ 3+ nanoparticles, energy transfer occurs from Tb to Ce [94]. Furthermore, in Ce 3+ co-doped 3+ 3+ 3+ Y 2 Sn 2 O 7 :Tb nanoparticles, strong energy transfer from Ce to Tb occurs only after covering the nanoparticles with SiO 2 [233]. This has been attributed to the diffusion of lanthanide ions towards the interface region between Y Sn O nanoparticles and silica. 2 2 7 103
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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
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(IR), visible and ultra-violet (UV)
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in Ce 3+ , Pr 3+ , Tb 3+ and CT abs
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assisted by lattice phonons of appr
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decay-time reduction is much easier
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nanocrystals is shown in Fig.10 [58
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depends strongly on the nature of t
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corresponding emission and excitati
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doped nanomaterials of the above me
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will be formed and subsequently it
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Eu 3+ ions were also subjected to s
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transferred into a two-necked RB fl
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Where λ is the wavelength of X-ray
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Micro-structural characterization b
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electrons (i.e. diffraction mode).
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diffraction spots. By tilting a cry
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surface. The contact mode can obtai
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three types lines in the scattered
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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
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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: Intensity(arb.units) 1.0 0.8 0.6 0.
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)
Page 155 and 156: growth centre compared to higher vi
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Page 159 and 160: 3+ 3+ concentration quenching. Tb l
Page 161 and 162: Compared to the selected area elect
Page 163 and 164: lattice. Lanthanide ions occupying
Page 165 and 166: obtained after 275 nm excitation is
Page 167 and 168: The luminescence dynamics associate
Page 169 and 170: that the broad peak can be resolved
Page 171 and 172: espectively. Value of this integral
Page 173 and 174: ethylene glycol moiety (stabilizing
Page 175 and 176: Room temperature and 100°C synthes
Page 177 and 178: heavier metal ion as compared to La
Page 179 and 180: Similar studies were also carried o
Page 181 and 182: 3+ 3+ faster decay component is ass
Page 183 and 184: the other hand the Eu 3+ lifetime h
Page 185 and 186: 3+ 4.4.8 Luminescence studies on Sm
Page 187 and 188: CHAPTER 5: Zinc gallate (ZnGa 2 O 4
Page 189 and 190: 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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CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

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