Magnetic and Spectroscopic Properties of Fe³⁺ and Mn²⁺ Doped in Model Quantum Dots

This dissertation is focused on the study of a series of paramagnetic materials from molecular to nanoscale with increasing number of transition metal ions. We have successfully used techniques like SQUID magnetometry, high frequency electron paramagnetic resonance (HFEPR) and magic angle spinning nuclear magnetic resonance (MAS NMR) to characterize series of samples. Initial work of this dissertation was focused on the molecular systems and its major part is dedicated to the study of transition ion doped Quantum Dots (QDs). The molecular systems discussed here are as follows: Vanadyl Phthalocyanine (VOPc), [H3M3+2(As3+W6O23)2(As3+O3)2]11- (M = Cr3+, Fe3+) and [H3Mn2+2(As3+W6O21)2(As3+O3)4]11-, X2Cr(dpa)4Cl2, (X = Cr, Mo and W), [M4(OH)2(H2O)2(α-SiW10O37)2]14- (M = Co2+, Ni2+, Zn2+). Following are the QDs samples: Fe3+ Doped ZnSe QDs, (Fe:ZnSe), Fe3+ Doped CdSe QDs, (Fe:CdSe), Mn2+ Doped ZnSe QDs, (Mn:ZnSe) and Al3+ Doped ZnSe QDs, (Al:ZnSe). Chapter 1 gives the motivation, overview and organization of this dissertation. Chapter 2 describes the techniques used in this undertaking. Chapter 3 is focused on molecular systems: Vanadyl Phthalocyanine (VOPc), [H3M3+2(As3+W6O23)2(As3+O3)2]11- (M = Cr3+, Fe3+) and [H3Mn2+2(As3+W6O21)2(As3+O3)4]11-, X2Cr(dpa)4Cl2, (X = Cr, Mo and W), [M4(OH)2(H2O)2(α-SiW10O37)2]14- (M = Co2+, Ni2+, Zn2+). Chapter 4-7 are focused on the nanoscale quantum dots samples. Chapter 4 describes correlation of structure and observed magnetic properties of local inclusions formed upon doping Fe3+ in ZnSe QDs. Chapter 5 reports probing dynamics of Mn2+ in ZnSe QDs using high frequency pulsed EPR spectroscopy. Origin of ferromagnetic and antiferromagnetic interactions in Fe3+ doped CdSe QDs is discussed in Chapter 6. Chapter 7 describes the use of MAS NMR in probing local sites Al3+ dopant in ZnSe QDs. Finally, Chapter 8 summarizes the major results and conclusions of this dissertation.