http://irgu.unigoa.ac.in/drs/handle/unigoa/5 2026-08-05T19:19:31Z 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/7899 Characterizations of additively graceful signed paths and cycles D'Souza, B.; Pereira, J. A (p,m,n) signed graph S, is a signed graph of order p with m positive edges and n negative edges. In this paper, we first prove a few basic results on vertex labelings of paths. We use these results and a sequence of lemmas to obtain a characterization of additively graceful signed paths. We prove that, apart from exactly 4 exceptions, additively graceful signed paths are characterized by the signed paths containing at most one negative section with n less than or equal to 2. We also establish a characterization of additively graceful signed cycles. We prove that a (p,m,n) signed cycle S is additively graceful if and only if one among the following 4 conditions are satisfied, (a) n=0 and m identical to 0 or 3 (mod 4), (b) n = 1 and m identical to 1 or 2 (mod 4), (c) n = 2, or 2 (mod 4) and S contains a single negative section, (d) S is the all negative signed cycle on C sub(3). 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