Department of Physics

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IIT Jodhpur

We study the phenomenon of deliberate inter-modal interactions in a specially designed index guided Microstructured Optical Fiber (MOF) by exploiting multipole expansion method (White et al. 2002). The MOF is designed in such a way that the first layer of holes is judiciously filled with a material having refractive index slightly greater than the background material or core and remaining holes are filled with air. Accordingly, we find an interesting phenomenon of mode crossing between the fundamental mode and a targeted defect mode while tuning the wavelength. Exploring this transition wavelength of the mode crossing, we propose a design of a fiber optic sensor for refractive index measurement (Silva et al. 2014) with enhanced sensitivity. © 2017, Springer-Verlag GmbH Germany, part of Springer Nature.

World University root node

Microsystem Technologies

Highly sensitive refractive index sensor based on degeneracy in specialty optical fibers: a new approach

The dynamical parametric encirclement around a second-order exceptional point (EP) enables the time-asymmetric nonadiabatic evolution of light, which follows the chirality of the underlying system. Such light dynamics in the presence of multiple EPs and the corresponding chiral aspect is yet to be explored. In this Letter, we report a gain–loss assisted four-mode-supported optical waveguide that hosts a parameter space to dynamically encircle multiple EPs. In the presence of multiple EPs, we establish a unique nonadiabatic behavior of light, where beyond the chiral aspect of the system, light is switched to a particular mode, irrespective of the choice of the input mode. Proposed scheme certainly opens a step-forward approach in light manipulation to facilitate next-generation integrated photonic systems. © 2020 Optical Society of America

Optics Letters

Chirality breakdown in the presence of multiple exceptional points and specific mode excitation

Abstract: In the present work, we have used hydrothermally synthesized in situ functionalized MoS2-QDs for a sensitive (limit of detection ~ 2.06 µM) and selective detection of Fe3+ ions. A detailed study of fluorescence quenching behavior for MoS2-QDs in the presence of Fe3+ ions has been performed using the Stern–Volmer plot, modified Stern–Volmer plot, and time-resolved photoluminescence measurements. Absorption based titration spectra and time-resolved photoluminescence measurements confirmed the fluorescence quenching is static with three decay times originated from the three different fluorescing sites. Interestingly, it is found that emission spectra consist of three bands at positions ~ 450 nm (P1, ~ 2.76 eV), ~ 475 nm (P2, ~ 2.61 eV), and ~ 503 nm (P3, ~ 2.46 eV). These peaks show a systematic quenching with the increasing concentration of Fe3+ ions. Quenching constants corresponding to these emission bands are found of the order of ~ 103 M−1. Large values of bimolecular quenching constants (~ 1011 M−1 s−1) suggest a strong binding interaction between MoS2-QDs and Fe3+ ions. Furthermore, to understand the fluorescence quenching of MoS2-QDs in the presence of Fe3+ ions, a ground-state complex formation-based mechanism has been proposed and elucidated in detail. Graphic abstract: [Figure not available: see fulltext.]. © 2020, Springer-Verlag GmbH Austria, part of Springer Nature.

Monatshefte f{\"{u}}r Chemie-Chemical Monthly

Fluorescence quenching of molybdenum disulfide quantum dots for metal ion sensing

Hydrogen bonding is an indispensable tenet in the fabrication of surface-confined physisorbed supramolecular networks. On-surface supramolecular chemistry is dominated by aromatic carboxylic acids, which allow implementation of highly directional and robust design elements in the form of hydrogen bonds. In this article, we investigate the influence of sterically enforced noncoplanarity of the carboxyl groups on the hydrogen-bonding ability and the self-assembly behavior of iodinated benzene tricarboxylic acid at the solution/graphite interface. The carboxylic groups of this acid are noncoplanar with respect to the benzene ring because of the bulky iodine atoms substituted on the ring. The self-assembled networks formed at the solution-solid interface were characterized at submolecular resolution using scanning tunneling microscopy (STM). The assembly behavior was scrutinized further by employing detailed molecular modeling simulations that provide an insight into the energetics of the self-assembled network formation. The on-surface mixing behavior of the iodinated, and the noniodinated analogue, the widely studied trimesic acid, was investigated. STM reveals that deposition of the two compounds on the graphite surface leads to phase separation orthogonal to the substrate and yields a supramolecular heterostructure with a well-defined bilayer. The present results indicate that, while the noncoplanarity induced by steric factor is not detrimental to the assembly behavior, it certainly contributes to the peculiar mixing behavior observed at the solution-graphite interface. © 2020 American Chemical Society.

The Journal of Physical Chemistry C

Coplanar versus Noncoplanar Carboxyl Groups: The Influence of Sterically Enforced Noncoplanarity on the 2D Mixing Behavior of Benzene Tricarboxylic Acids

In recent years, inorganic semiconductor quantum dots (QDs) have garnered significant attention of scientific diaspora owing to their unique photophysical properties. In this series, SnS2-QDs are predicted as one of the promising inorganic quantum dots. However, investigation on the photoluminescence property of SnS2 QDs and its biosensing applications is limited. Therefore, it needs serious exploration. In this work, we report the synthesis of in-situ functionalized fluorescent tin disulfide quantum dots (f-SnS2 QDs) using one-step bottom-up hydrothermal technique. The obtained f-SnS2 QDs are monodispersed in nature and exhibits strong blue fluorescence under UV exposure with a high quantum yield (QY ~8.7%) in aqueous medium. Interestingly, it is observed that fluorescence of f-SnS2 QDs significantly quenched in the presence of Fe3+ ions. The developed optical sensor shows linear response for Fe3+ ions in the concentration range of 0 μM–68 μM (~0.84 μM detection limit). Further, to understand the quenching kinetics, the PL and TRPL studies are conducted which reveal that the quenching phenomenon is both static as well as dynamic in nature. The underneath detailed mechanism is also discussed in the paper. © 2020 Elsevier B.V.

Optical Materials

Facile synthesis of highly fluorescent water-soluble SnS2 QDs for effective detection of Fe3+ and unveiling its fluorescence quenching mechanism

We make a detailed analysis of quantumness for various quantum noise channels, both Markovian and non-Markovian. The noise channels considered include dephasing channels like random telegraph noise, non-Markovian dephasing and phase damping, as well as the non-dephasing channels such as generalized amplitude damping and Unruh channels. We make use of a recently introduced witness for quantumness based on the square l1 norm of coherence. It is found that the increase in the degree of non-Markovianity increases the quantumness of the channel. This may be attributed to the fact that the non-Markovian dynamics involves the generation of entanglement between the system and environment degrees of freedom. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.

Fulltext

Quantum Information Processing

Coherence-based measure of quantumness in (non-) Markovian channels

We study the effects of non-standard neutrino matter interactions on the coherence of oscillating neutrino-system in a model independent way in the context of upcoming DUNE experiment. We find that the LMA-LIGHT solution (with normal ordering of mass eigenstates) decreases the coherence in the system in comparison to the standard model prediction for almost all values of neutrino energy E and CP violating phase $$\delta $$. However, a large enhancement in coherence parameter in the entire $$(E-\delta )$$ plane is possible for the DARK octant of $$\theta _{12}$$ for inverted ordering, with a protuberant enhancement at $$E \sim $$ 4 GeV, where maximum neutrino flux is expected in the DUNE experiment. Such features make neutrino a promising candidate for carrying out quantum information theoretic tasks. © Springer Nature Singapore Pte Ltd 2020.

Springer Proceedings in Physics

Effects of nonstandard interactions on coherence in neutrino oscillations

Supercapacitors (SCs) are energy storage devices with high power density and robust charge/discharge life cycles. The high power density of these energy storage devices makes them attractive storage devices in conjunction with other reversible electrical energy storage devices such as batteries and conventional capacitors. The common SCs are made of nanostructured carbonous electrode materials, which are limited with their relatively lower operating window and specific energy densities. Nanostructured metal oxide based carbonous composites are widely explored to overcome carbonous SCs. Rare earth (RE) oxides such as Nd2O3, Y2O3, and Eu2O3 are used in conjunction with carbonous/conducting polymers matrix for high specific density and operating voltage supercapacitors. The high band gap of RE oxides assists in achieving higher operating voltage window. The article will review the current status of RE oxide based supercapacitors and their physical properties in conjunction with underlying physical principles. © 2020, Springer Nature Singapore Pte Ltd.

Smart Innovation, Systems and Technologies

Rare Earth Oxides Based Composites for High Voltage Supercapacitors Applications: A Short Review

The generation, control and transfer of triplet excitons in molecular and hybrid systems is of great interest owing to their long lifetime and diffusion length in both solid-state and solution phase systems, and to their applications in light emission1, optoelectronics2,3, photon frequency conversion4,5 and photocatalysis6,7. Molecular triplet excitons (bound electron–hole pairs) are ‘dark states’ because of the forbidden nature of the direct optical transition between the spin-zero ground state and the spin-one triplet levels8. Hence, triplet dynamics are conventionally controlled through heavy-metal-based spin–orbit coupling9–11 or tuning of the singlet–triplet energy splitting12,13 via molecular design. Both these methods place constraints on the range of properties that can be modified and the molecular structures that can be used. Here we demonstrate that it is possible to control triplet dynamics by coupling organic molecules to lanthanide-doped inorganic insulating nanoparticles. This allows the classically forbidden transitions from the ground-state singlet to excited-state triplets to gain oscillator strength, enabling triplets to be directly generated on molecules via photon absorption. Photogenerated singlet excitons can be converted to triplet excitons on sub-10-picosecond timescales with unity efficiency by intersystem crossing. Triplet exciton states of the molecules can undergo energy transfer to the lanthanide ions with unity efficiency, which allows us to achieve luminescent harvesting of the dark triplet excitons. Furthermore, we demonstrate that the triplet excitons generated in the lanthanide nanoparticle–molecule hybrid systems by near-infrared photoexcitation can undergo efficient upconversion via a lanthanide–triplet excitation fusion process: this process enables endothermic upconversion and allows efficient upconversion from near-infrared to visible frequencies in the solid state. These results provide a new way to control triplet excitons, which is essential for many fields of optoelectronic and biomedical research. © 2020, The Author(s), under exclusive licence to Springer Nature Limited.

Nature

Lanthanide-doped inorganic nanoparticles turn molecular triplet excitons bright

Organometal halide perovskites are being extensively studied as they can serve as an excellent active medium in various optoelectronic devices such as solar cells, light-emitting diodes (LEDs), lasers, etc. We report the fabrication of highly controlled single-phase mixed halide two-dimensional (2D) perovskites by successive doping of inorganic dopant, potassium iodide (KI), in 2D perovskite 2-(1-cyclohexenyl) ethylammonium lead bromide, (C6H9C2H4NH3)2PbBr4 (CHPB). Our computational investigations further confirm the thermodynamic stability of mixed anion lattices. A stoichiometric increase of KI in CHPB beyond critical passivation levels results in a uniform bandgap tunability of thin films from the UV (∼3.21 eV) to green (∼2.50 eV) region of spectra. Distinctly linear, tunable, and single-phase strong room-temperature exciton absorbance (∼401−508 nm) and emission peaks (∼416−518 nm) in the blue-green spectral region are observed with the increase of KI concentration levels in thin-film samples. Doped two-dimensional (2D) perovskite films exhibit a minimum stokes shift parameter of 40 meV, which is very small compared to the conventional route of mixing two perovskite precursor solutions. X-ray diffraction studies show that the layered structure of doped 2D perovskite thin films remains intact despite high KI concentration levels. Charge transport studies of doped 2D perovskite thin films demonstrate a decline in the lifetime of photogenerated charge carriers with an increase of iodide concentration. Combining several experimental and computational techniques, we find that increased carrier effective masses and consequent formation of strongly bound excitons cause the decrease in carrier lifetime. In short, our present study reveals a promising low-cost solution-processable approach to fabricate single-phase mixed halide 2D perovskites to achieve unprecedented exciton tunability in low-dimensional optoelectronic materials. © 2020 American Chemical Society