CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

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In order to check this aspect, these nanomaterials are doped with representative lanthanide ion namely the Eu 3+ and their luminescence properties are described in the following section. (a) (b) (c) (d) Fig.107. TEM image of (a and b) CaWO 4 , (c) SrWO 4 and (d) BaWO 4 nanomaterials and inset of the images shows corresponding SAED pattern. 6.3. Effect of metal ion on luminescence of MWO 4 :Eu 3+ nanoparticles: Emission spectra of Eu 3+ doped MWO 4 (M = Ca, Sr, Ba) nanoparticles excited at 270 nm is given in the Fig.108 (a). It consists of four peaks at 590, 615, 650 and 700 nm and are attributed to 5 D 0 Æ 7 F 1 , 5 D 0 Æ 7 F 2 , 5 D 0 Æ 7 F 3 and 5 D 0 Æ 7 F 4 transitions of Eu 3+ ions present in the lattice. The 5 D 0 Æ 7 F 2 transition is electric dipole allowed transition. It is hypersensitive and is highly dependent on the symmetry around the Eu 3+ ion. Unlike this, 5 D 0 Æ 7 F 1 transition is a magnetic dipole allowed transition and is independent of the symmetry around Eu 3+ ion in the 168
lattice. Asymmetric ratio is ~ 12 for all the three tungstates. High value of asymmetric ratio indicates that Eu 3+ ion occupies a highly asymmetric environment in MWO 4 (M = Ca, Sr, Ba) crystal lattice. The intensity of Eu 3+ emission decreases with increase in the ionic size of the alkaline earth metal cations. Similar effect was observed by Blasse, et al. for UO 6 emission in the tungstate host [69]. Presence of ions with large radius around the luminescent center is equivalent to soft surroundings. With increase in the softness of surroundings, stokes shift increases and as a result the excited tungstate group decays by a non-radiative route to ground state instead of transferring energy to lanthanide ions. This explains the decrease in luminescence intensity when going from CWO 4 to SrWO 4 and then to BaWO 4 . It is also known that with increase in the stiffness of the lattice, non-radiative process decreases. Intensity (arb.units) 20000 16000 12000 8000 4000 5 D 0 5 D 0 7 F 1 7 F 2 5 D 0 λ exc = 270 nm 7 F 3 CaWO 4 :Eu 3+ SrWO 4 :Eu 3+ BaWO 4 :Eu 3+ 5 D 0 7 F 4 0 550 600 650 700 750 Wavelength (nm) (a) Intensity (arb.units) (b) 80000 60000 40000 20000 0 λ em : 615 nm CaWO 4 :Eu 3+ SrWO 4 :Eu 3+ BaWO 4 :Eu 3+ 200 250 300 350 400 Wavelength (nm) Fig.108. (a) Emission spectra and (b) excitation spectra from CaWO 4 : Eu 3+ , SrWO 4 : Eu 3+ , BaWO 4 : Eu 3+ nanoparticles. (λ exc = 270 nm and λ em = 615 nm) In the present case the ionic radii of metal ion increases while going from CaWO 4 to SrWO 4 and then to BaWO 4 . Hence, the stiffness of the lattice decreases in the same order and this explains the observed maximum in the luminescence intensity from CaWO 4 as compared to SrWO 4 and BaWO 4 . Values of lattice parameters further confirm this. The excitation spectra corresponding to Eu 3+ emission is shown in Fig.108 (b). The patterns consist of broad peak centered at 270 nm and sharp peaks above 310 nm. The broad band is assigned to the Eu-O 169
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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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(001) (110) (011) (101) (020) (101)
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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 and 204: CHAPTER 6: Tungstates [MWO 4 (M = C
Page 205: ionic radius of the metal cation ca
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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CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

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