CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

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found to be 0.97. A comparison of the emission spectrum shown in Fig.56 (b and c) suggests that Eu 3+ 3+ ions exist as a separate EuPO 4 phase in 5 at % Eu containing sample. However, for 2.5 at % Eu 3+ containing sample, the asymmetric ratio of luminescence is quite different from EuPO 3+ phase, suggesting that Eu ions are in a different environment in GaPO 4 4 nanoparticles containing 2.5 at % Eu 3+ . Presence of Eu 3+ ions during precipitation reaction to form GaPO 4 can either lead to the formation of europium hydroxide phase or result in replacing protons of the surface hydroxyl groups attached to surface gallium or phosphorus species present on the nanoparticles. In order to check the first possibility, Eu 3+ ions were subjected to hydrolysis in glycerol medium using urea as the reagent for hydroxide formation (urea and not ammonium dihydrogen phosphate was used for precipitation to prevent the formation of EuPO 4 phase). Emission spectrum from the sample obtained after 260 nm excitation is shown in Fig.57. The asymmetric ratio of luminescence is found to be 4.2 which is significantly higher than the 3+ value 2.2 observed from GaPO4 nanoparticles containing 2.5 at % Eu ions. These data suggest that Eu 3+ ions do not exist as europium hydroxide phase along with the GaPO 4 nanoparticles. 600 5 D 0 7 F 2 Intensity 400 200 5 D 0 7 F 1 5 D 0 7 F 4 0 500 550 600 650 700 750 Wavelength (nm) Fig.57 Emission spectrum of europium hydroxide sample prepared in glycerol medium by the identical method as that employed for GaPO 4 and EuPO4 nanoparticles, except that urea rather than ammonium dihydrogen phosphate was used to create the alkaline environment and to prevent the formation of EuPO 4 phase. 108
The second possibility is the exchange of protons of OH groups attached to phosphorus or gallium ion at the surface of GaPO 4 nanoparticles. Such ion exchange process is expected to affect the electronic environment around P and this will be reflected in the 31 P Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectrum of the samples. Hence the 31 P MAS NMR patterns of the samples were recorded and are described below. 31 4.2.3 P MAS NMR studies: Figure 58 shows the 31 P MAS NMR patterns of GaPO 4 nanoparticles containing different amounts of Eu 3+ ions. As prepared GaPO 4 sample showed a sharp peak around δ -10 ppm with weak shoulder around -6 ppm in the 31 P MAS NMR spectrum (Fig.58 (a)). Based on the previous 31 P MAS NMR studies on GaPO and Al Ga 4 x 1- xPO 4 samples [236, 237] the peak at -10 ppm has been attributed to the P structural units having four Ga 3+ ions as its next nearest neighbors (first neighbor being the oxygen atom). The weak shoulder has been attributed to P structural units existing at the surface of the nanoparticles which have got linkages with the OH groups. Shoulder peak is more broadened compared to the main peak, due to the strong dipolar interaction between 31 1 P and H nuclei. With incorporation of 2.5 at % Eu 3+ , the peak maximum of the main and shoulder peaks remained same, however their line widths are higher compared to GaPO 4 nanoparticles (Fig.58 (b)). With increase in Eu 3+ concentration, the line width of the peak increases and the shoulder is merged with the main peak around -10 ppm (Fig.58 (c and d)) due to increased line broadening. The peak maximum is found to be same for all the samples confirming that neither there is any solid solution formation between GaPO 4 and EuPO4 nor there is any formation of P-O-Eu 3+ linkages. Broadening of the peaks can be attributed to the existence of paramagnetic europium species along with the GaPO 4 nanoparticles. EuPO4 phase formation, as revealed by luminescence studies for samples containing higher Eu 3+ contents (5% or more), could not be confirmed by 31 P MAS NMR as it showed no resonance signal due to the higher extent of paramagnetic broadening brought about by the presence of four europium 109
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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
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
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: 5 D 0 7 F 2 level to 7 F 7 7 1 , F
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
Page 157 and 158: observed after excitation at 250 an
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
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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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