http://irgu.unigoa.ac.in/drs/handle/unigoa/28 2026-09-23T17:17:15Z http://irgu.unigoa.ac.in/drs/handle/unigoa/7994 Site-selective control of martensitic transition in MnCoGe: Decoupling Mn-Mn exchange and electronic hybridization Azavedo, M.; Dias, E.T.; Priolkar, K.R. The microscopic origin of the martensitic transition (MST) in MnCoGe remains unresolved due to the intertwined roles of lattice distortion, magnetic exchange, and electronic structure. In this work, we employ site-selective substitution - Ni at Mn and Co sites, and Cu at the Co site to decouple these competing effects. Synchrotron X-ray diffraction and X-ray absorption spectroscopy reveal that Ni substitution at the Mn site suppresses the MST by reducing the Mn-Mn interatomic distance, thereby stabilizing the hexagonal phase through enhanced ferromagnetic exchange. In contrast, Cu substitution at the Co site suppresses the MST without significant lattice contraction, instead weakening p-d hybridization, as evidenced by systematic changes in near-edge spectra. Ni substitution at the Co site induces only minor structural and electronic modifications, preserving the MST. These findings demonstrate that the martensitic transition in MnCoGe is governed by a competition between Mn-Mn exchange interactions and the electronic band energy associated with hybridization, both of which are strongly site-dependent. 2026-01-01T00:00:00Z http://irgu.unigoa.ac.in/drs/handle/unigoa/7923 Phase Transitions in Bose-Hubbard Models in Driven Optical Lattices Shettigar, Sheshgiri S 2025-09-01T00:00:00Z http://irgu.unigoa.ac.in/drs/handle/unigoa/7908 Structural Insights into AgBi(SC sub(12)H sub(25))sub(4) Mixed-Metal n-Alkanethiolate: Heterometallic Thiolate Bridging and Metallophilic Interaction-Directed Self-Assembly Das, M.; Mukherjee, M.; Das, S.; Datta, A.; Priolkar, K.R.; John, N.S.; Prasad, B.L.V. Long-chain metal n-alkanethiolates (MTs) are inorganic-organic hybrid materials, characterized by a metal-sulfur inorganic central plane sandwiched between hydrocarbon bilayers. Though MTs are known for over a century now, their crystal structures are conclusively established only recently. Mixed-metal thiolates (MMTs) are structurally similar to MTs and contain heterometals in the inorganic plane. With a very limited number of MMTs explored to date, their structures remain completely unknown. Here we report the synthesis and structural elucidation of a mixed-metal thiolate, AgBi(SC sub(12)H sub(25))sub(4), providing direct insight into heterometal arrangement by combining X-ray absorption fine structure spectroscopy and density functional theory calculations. The results establish that the AgBi MMT contains discrete molecular units like [RS-Ag-SR-Bi(SR) sub(2)] containing both Ag and Bi metals with an intramolecular heterometallic Mu sub(2)-thiolate bridging. The units further share strong intermolecular Ag...Bi metallophilic interactions at a very short distance of 2.72 angstrom, playing a crucial role in the self-assembly. Intermolecular metal-to-metal charge transfer occurring both directly and via the thiolate bridge gives rise to the absorption maxima observed in the UV-Vis spectrum. The intermolecular interactions predominantly arise from the thiolate group (RS-) of one unit interacting with the Ag sup(+) and Bi sup(3+) centers of the adjacent units, in addition to the Ag...Bi metallophilic interaction. 2026-01-01T00:00:00Z http://irgu.unigoa.ac.in/drs/handle/unigoa/7841 Plasmon-enhanced fluorescence for sensitive and selective mercury ion (Hg sup(2+)) detection Bandekar, S.N.; Vij, R.; Prabhu, S.; Achanta, V.G.; Sahu, S.; Jha, R.; Sudhir, C. Plasmon-enhanced fluorescence (PEF) has emerged as an interesting platform for biosensing and quantum applications. The strong enhancement of emission from fluorophores arises due to an increase in the excitation and radiative decay rates of fluorophores in the vicinity of the metal surface. Furthermore, the excitation of surface plasmons on the metal accentuates the enhancement mechanism. A PEF-based system combines high sensitivity, photostability, and selectivity, making it a promising candidate for environmental monitoring and for the detection of trace levels of mercury ions (Hg sup(2+)) in aqueous media. Here, we report a study on PEF of CdSe-ZnS core-shell quantum dots and Rhodamine B (RhB) using silica-coated gold nanoparticles. Our observations indicate a strong enhancement in the emission intensity of these fluorophores in the vicinity of the metal nanoparticles. Along with this increase in intensity, there is a decrease in the emitter's lifetimes when mixed with the metal nanoparticles. Our study also shows that the enhancement is maximum at the plasmonic resonance wavelength, implying that this is indeed a plasmon-enhanced process. We performed finite-difference time-domain (FDTD) simulations to numerically investigate the electric-field enhancement in the immediate vicinity of silica-coated gold nanostructures and to determine the spontaneous emission characteristics of emitters. Furthermore, we use this mechanism to detect Hg sup(2+) at ultra-low levels in aqueous media. The system leverages PEF and dynamic quenching mechanisms to achieve a limit of detection (LOD) in the femtomolar (fM) range, surpassing previously reported nanocomposite-based sensors. 2026-01-01T00:00:00Z