CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

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een prepared. Synthesis and luminescence properties of these nanoparticles are discussed in this chapter. Tungstate nanomaterials were prepared at room temperature in ethylene glycol by adding sodium tungstate to the metal nitrate solution. 6.2. Effect of nature of metal ion on the particle size: Figure 106 shows XRD patterns of MWO 4 (M = Ca, Sr, Ba) nanomaterials. All the peaks are characteristic of nanocrystalline tetragonal MWO 4 with scheelite structure. The shifting of XRD peak maximum to lower 2θ values from Ca to Ba through Sr is due to the increase in the ionic radii of cation and associated lattice expansion. Line widths of diffraction peaks are also found to decrease with increase in the ionic radii of the metal ion. Average crystallite size was calculated by using Debye-Scherrer formula and is found to be 7, 10, 20 nm for CaWO 4 , SrWO 4 and BaWO 4 , respectively. BaWO 4 Intensity (arb.units) (101) (112) (004) (200) (211) (213) (204) (220) (116) SrWO 4 CaWO 4 (312) (321) 10 20 30 40 50 60 70 2θ/° Fig.106. XRD patterns of MWO 4 (M = Ca, Sr, Ba) nanoparticles. Lattice parameters were calculated by least squares fitting of the XRD patterns. These are found to be a = 5.240Å, c = 11.381 Å for CaWO 4 , a = 5.415 Å, c = 11.951 Å for SrWO 4 and a = 5.613 Å, c = 12.703 Å for BaWO 4 nanoparticles. The increase in the lattice parameters are due to increase in the ionic sizes of metal ions. Increase in particle size with increase in 166
ionic radius of the metal cation can be explained based on the difference in the extent of stabilization of ligand (EG moiety) on the surface of MWO 4 nanoparticles. As the stabilization of EG moiety on the nanoparticles occurs through cations like Ca 2+ , Sr 2+ and Ba 2+ , the extent of stabilization of ligand will be the highest for CaWO 4 nanoparticles and lowest for BaWO 4 nanoparticles, due to the so called hard-hard and soft-soft interactions. Extent of stabilization of ligands with SrWO 4 is in between that of CaWO 4 and BaWO 4 . Higher the extent of stabilization, lower will be the extent of growth and this result in smaller particles. TEM images of CaWO 4 , SrWO 4 and BaWO 4 nanomaterials are shown in Fig.107. CaWO 4 nanoparticles are relatively small with size in the range 5-10 nm and have uniform size distribution as can be seen in Fig.107 (a). The SAED pattern from these nanoparticles is shown in the inset of Fig.107 (a). The pattern consists of several rings, which are characteristic of very fine particles that are randomly oriented. HRTEM image of CaWO 4 nanoparticles is shown in Fig.107 (b). Distance between lattice fringes is found to be 3.1 Å and this matches well with that of (112) plane of CaWO 4 . TEM image of SrWO 4 nanoparticles is shown in Fig.107 (c). It is clear from the image that particles have homogeneous size distribution with sizes in the range of 15-25 nm. Corresponding SAED pattern is shown in the inset of Fig.107 (c), consists of both rings, and dots characteristic of nanocrystalline SrWO 4 phase with slight aggregation. TEM image of BaWO 4 nanoparticles is shown in Fig.107 (d). These particles are having rice shape with length around 500-1000 nm. SAED pattern from BaWO 4 nanoparticles is shown in the inset of Fig.107 (d) and the pattern mainly consists of dots and is characteristic of single crystalline nature of BaWO 4 nanomaterials. Based on XRD and TEM studies it is inferred that CaWO 4 nanoparticles are extremely small in size compared to other two tungstates. It would be of interesting to assess the MWO 4 nanomaterials which can give optimum luminescence on lanthanide ion doping. 167
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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
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sample fluoresce. The fluorescent l
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pulse frequency) as excitation sour
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Lanthanide ions doped Ga 2 O 3 nano
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atoms at three corners and the lone
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Figure 19 (a-d) shows SEM images of
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Based on these results, it can be i
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almost normal to the equatorial pla
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Table 2. Summary of important modes
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systematic disappearance of these t
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comparison, Eu 3+ ions alone in wat
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the samples, suggesting that Eu 3+
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These inferences are further substa
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Similar DTA peaks have been reporte
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GaOOH samples doped with different
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The cell parameters increases with
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strong emission compared to corresp
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curves are shown in Fig.39. Lifetim
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Similar results are also observed f
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intensity of XRD peaks correspond t
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compared to the bulk material and a
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is almost 1½ times that of peak B1
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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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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
Page 191 and 192: water content in the reaction mediu
Page 193 and 194: nucleation, thereby leading to incr
Page 195 and 196: particles. Thus the TEM studies als
Page 197 and 198: value. The lattice parameters calcu
Page 199 and 200: Quantum yield of the blue emission
Page 201 and 202: 5.5.2. Eu 3+ doped ZnGa 1.5 In 0.5
Page 203: CHAPTER 6: Tungstates [MWO 4 (M = C
Page 207 and 208: lattice. Asymmetric ratio is ~ 12 f
Page 209 and 210: 700 Intensity (arb.units) 600 λ ex
Page 211 and 212: Intensity (arb.units) 25000 20000 1
Page 213 and 214: Strong green emission has been obse
Page 215 and 216: consists of strong band at 255 nm a
Page 217 and 218: peak can be attributed to the cryst
Page 219 and 220: nm) is observed from Er 3+ doped Ga
Page 221 and 222: and Dy 3+ doped CaWO 4 nanoparticle
Page 223 and 224: REFERENCES 1. D. J. Barber, I. C. F
Page 225 and 226: 32. K. A. Gschneidner, Jr., L. Eyri
Page 227 and 228: 65. Z. Deng, F. Tang, D. Chen, X. M
Page 229 and 230: 100. A. Rouanel, J. J. Serra, K. Al
Page 231 and 232: 130. F. Li, W. Jianhuai, L. Jiongti
Page 233 and 234: 166. L. Fu, Z. Liu, Y. Liu, B. Han,
Page 235 and 236: 205. R. Sasikala, V. Sudarsan, C. S
Page 237 and 238: 238. E. Oldfield, R. A. Kinsey, K.
Page 239 and 240: 271. B. G. Hyde, S. Andersson, ”I
Page 241 and 242: B. S. Naidu, B. Vishwanadh, V. Suda
Page 243: 9. Room temperature synthesis of mu
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