CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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137 absorption studies that on formation type II shell absorption peak moves towards to red region of the spectrum. As we have discussed that on formation shell surface state emission are drastically reduced so the emission observed in these type II core shell are due to “indirect” emission where electrons reside in the CdSe core and hole in ZnTe shell. Earlier Kim et al [5.2] reported gradual red shift of type II core shell emission in CdTe/CdSe coreshell with increasing shell thickness. We can still see further red shift in emission spectra for CdSe/ZnTe3 core-shell in Figure 4d. We have also excited CdSe/ZnTe4 core-shell to find out the emission band. The emission could not be detected in the visible region as the emission might be appearing in the near-IR region which beyond the detection limit of our instrument. PL Intensity (a.u.) 1.5 1.0 0.5 b c d a 0.0 525 600 675 750 Wavelength (nm) Figure 4: Normalized steady state emission spectra of a) CdSe (thick solid line), b) CdSe/ZnTe1 (short dash), c) CdSe/ZnTe2 (dash dot), and d) CdSe/ZnTe3 (dash-dot-dot).
138 5.3.3. Time resolved emission studies: To ascertain influence of shell formation on the recombination dynamics we have carried out time-resolved emission studies for CdSe QD and CdSe/ZnTe core-shell material of different thickness and the emission decay kinetics are shown in Figure 5.5. It is clear from the kinetic decay trace that on shell formation emission lifetime increases in core-shell materials. It is clear from our observation that the recombination dynamics for the photoexcited electron-hole pairs is longer in Cdse/ZnTe core shell as compared to the CdSe core. Similar observation we made in our earlier investigation [5.19] where the emission life time of CdTe/CdS type II core-shell drastically increased as compared to CdTe core. In the present studies we have compared emission decay kinetics for CdSe QD and CdSe/ZnTe1 (thinnest shell) and CdSe/ZnTe3 (thick shell). For all samples time resolved emission measurement has been done at their peak emitting wavelengths and exciting at 454 nm. The emission decay kinetics for CdSe can be fitted multi-exponentially with time constants τ 1= 0.50 ns (59%), τ 2 = 3.8 ns (34%), τ 3= 17.4 ns (7%) with average time (τ av) of 2.8 ns (Figure 5a). Figure 5b shows the emission decay kinetics for CdSe/ZnTe1 (thinnest shell) which can be again fitted multi-exponentially with time constants τ 1= 0.60 ns (65%), τ 2= 3.7 ns (18.6%), τ 3= 16.3 ns (16.4%) with average time (τ av) of 3.75 ns.
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Charge Transfer Dynamics in Quantum
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DECLARATION I, hereby declare that
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ACKNOWLEDGEMENTS It is my privilege
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1.3.5. Defect Mediated Relaxation 2
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2. 8. 4. White Light Generation- 45
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6.2. Experimental 6.2.1.Synthesis o
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devices based on QDs it has been sh
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Furthermore generation of pump (~40
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shell). This clearly indicated that
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12. V. I. Klimov, J. Phys. Chem. B,
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1.13 Reactant and Product Potential
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light. Inset: Kinetic traces monito
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6.5 Transient decay kinetics of gra
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at 670 nm after exciting at 400 nm
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ABBREVIATIONS BET BQ CB CCD CdS CdT
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1 Chapter 1
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3 size dependent optical properties
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5 1.2. Physics of Semiconductors 1.
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7 As seen from the schematic, poten
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9 Substituting this in Schrödinger
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11 ( r, r ) ( r ) ( r ) (1.13) e
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13 E E E 2 2 2 EX ne, le nh,
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15 spherical symmetry of field. The
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17 gE ( ) 2Em 2 3 3 (1.25) For a
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19 1.3.2. Electron-Hole energy tran
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21 Impact Ionization Figure 1.7. Sc
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23 understanding on mechanistic asp
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25 carriers are unable to sample th
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27 CB VB QD Metal Figure. 1. 10. Sc
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29 energy barrier. Therefore it is
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31 1 f q 2 A qB (1.30) 2 In equa
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33 Vibrational contribution can be
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35 1. 7. 1. Electron Injection ET i
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37 Under assumption of invariance o
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39 distribution. To achieve good si
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41 initially achieved monodispersit
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43 and rate of charge transfer acro
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45 1.32 P. V. Kamat, J. Phys. Chem.
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47 Chapter 2
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49 chemical species. Since a partic
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51 fluorescence forms an important
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53 eliminated by use of standard wh
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55 sample. Raman spectroscopy is ba
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57 will appear bright and region wi
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59 volatile solvent is drop casted
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61 spots arise from diffraction fro
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63 The electrical signal is then ch
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65 delayed and inverted. The two si
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67 Pump-probe technique is one of t
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69 Amplifier Jade Stretcher fs Osci
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71 Figure 2.6. Optical layout of Ti
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73 Grating Convex Mirror Concave Mi
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75 changes the polarization from ho
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77 Grating Output Input Mirror Grat
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79 μJ has a very high peak power.
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81 2.6. Dynamical Theory of X-Ray D
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83 Chapter 3
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85 Therefore the study of interfaci
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87 3. 2. Experimental Section 3.2.1
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89 and intensity show absence of ot
Page 134 and 135: 91 which is also neutral; therefore
Page 136 and 137: 93 electron transfer times. This re
Page 138 and 139: 95 r B a * 0 3.1 me / me Now the
Page 140 and 141: 97 nonadiabatic case the electron t
Page 142 and 143: 99 drastically reduced leading to a
Page 144 and 145: 101 While the study of injection dy
Page 146 and 147: 103 study. Based on the injection d
Page 148 and 149: 105 17. L. E. Brus, J. Phys. Chem.
Page 151: 107 Chapter 4
Page 154 and 155: 109 of the QDs. As a result surface
Page 156 and 157: 111 4.2.2. Synthesis: The CdTe QDs
Page 158 and 159: 113 lower hole state. In CdSe the l
Page 160 and 161: 115 4.2 inset. The kinetic traces a
Page 162 and 163: 117 growth of the bleach kinetics (
Page 164 and 165: 119 previous section we have discus
Page 166 and 167: 121 lived charge transfer complex w
Page 168 and 169: 123 100 times concentration of the
Page 170 and 171: 125 4.5. References 4.1. Efros, Al.
Page 173: 127 Chapter 5
Page 176 and 177: 129 been made in the synthesis of t
Page 178 and 179: 131 metallic synthesis by arrested
Page 180 and 181: 133 5.3. Result and discussion: 5.3
Page 182 and 183: 135 indicating a confinement induce
Page 186 and 187: 139 1000 c b PL Intensity 100 10 a
Page 188 and 189: 141 samples due to a very weak exci
Page 190 and 191: 143 dynamical spectrum is negligibl
Page 192 and 193: 145 Earlier authors [5.4] reported
Page 194 and 195: 147 Sample t r(ps) t 1(ps) t 2(ps)
Page 196 and 197: 149 In addition to the cooling dyna
Page 198 and 199: 151 pulse-width time scale followed
Page 200 and 201: 153 5.20. Sreejith Kaniyankandy, Sa
Page 203 and 204: 155 CHAPTER 6 Charge Separation in
Page 205 and 206: 157 Studies by Wang et. al. [6.15]
Page 207 and 208: 159 graphene in a 1M NaOH solution.
Page 209 and 210: 161 Intensity (a.u.) 5 4 3 2 1 CdTe
Page 211 and 212: 163 dynamics of graphene oxide and
Page 213 and 214: 165 GO as shown in the Figure 3 rev
Page 215 and 216: 167 electron acceptor for Graphene.
Page 217 and 218: 169 governs the recombination dynam
Page 219 and 220: 171 Sample τ 1 (ps) τ 2 (ps) τ 3
Page 221 and 222: 173 A (mO.D) 10.0 0.0 -10.0 -20.0 0
Page 223 and 224: 175 involved in the relaxation may
Page 225 and 226: 177 Electron quencher (benzoquinone
Page 227 and 228: 179 Scheme 6.1. Schematic of Electr
Page 229 and 230: 181 6.6. Reina, A.; Jia, X.; Ho, J.
Page 231: 183 6.26. Kaiser, A. B.; Navarro, C
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185 assigned to injection into diff
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187 transfer from CdSe core to ZnTe
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189 However the position of bands i
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