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T.C. Pant

Bio: T.C. Pant is an academic researcher from Kumaun University. The author has contributed to research in topics: Acceptor & Rhodamine 6G. The author has an hindex of 10, co-authored 13 publications receiving 321 citations.

Papers
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TL;DR: In this paper, it was shown that a linear quenching of fluorescence intensity and decay time of salicylic acid doped polyvinyl alcohol (PVA) film in the presence of moisture or water in the organic solvents can be useful as an optical sensor for determination of humidity in the range 5%-85% and water contents in these solvolents in the ranges 1%-60% with an accuracy of (0.2%).
Abstract: Photoluminescence of salicylic acid (SA) and its sodium salt in poly(vinyl alcohol) (PVA) film and its quenching by water/moisture has been studied by steady-state and time domain fluorescence measurements. The results suggest that salicylic acid is completely ionized and present as a monoanion in PVA film, having a molar extinction coefficient (max) of 3545 M -1 cm -1 , and its emission shows a large Stokes shifted (8300 cm -1 ) fluorescence band with a quantum yield (f) of 0.34 and a decay time (Uf) of 6.7 ns. This emission band is due to excited-state intramolecular proton transfer (ESIPT) and is found to be sensitive to moisture and water contents in organic solvents. The films dipped in organic solvents, viz. dioxane, ethanol, and acetonitrile, containing water shows Stern-Volmer type fluorescence quenching. It is shown that a linear quenching of fluorescence intensity and decay time of SA doped PVA film in the presence of moisture or water in the organic solvents can be useful as an optical sensor for determination of humidity in the range 5%-85% and water contents in these solvents in the range 1%-60% with an accuracy of (0.2%. The response time of the sensor film is about 2 min, and recovery time is less than 1 min.

94 citations

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TL;DR: In this article, a dye pair (acriflavine and rhodamine 6G) doped in an ion exchange polymer matrix (Nafion®) has been investigated from the viewpoint of fabrication of an optical pH sensor.
Abstract: Excitation energy transfer, between a dye pair (acriflavine and rhodamine 6G) doped in an ion exchange polymer matrix (Nafion®), has been investigated from the viewpoint of fabrication of an optical pH sensor. The study is done by steady state as well as time domain fluorescence measurements. Using fixed donor–acceptor concentration, excitation energy transfer in the pH range 2–12 has been found to follow Forster function for dipole–dipole interaction. Further, pH has been calibrated by the energy transfer parameters, e.g. overlap integral ΩDA, energy transfer efficiency ηT, rate of energy transfer KR, critical transfer distance R0A and reduced concentration γ0A in the range 2–12 and is found to show an approximately linear dependence. These results in Nafion® matrix are similar to those found by us in solution [Sens. Actuators: B Chem. 63 (2000) 18]. The system appears to be attractive for optical pH sensor with reversibility and sensitivity of 0.01 pH units.

39 citations

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TL;DR: In this paper, the effect of hydrogen bonding, taking diethyl ether (Et 2 O) as the hydrogen-bonding partner, on the dual emission of salicylic acid (SA) was investigated with both steady-state and time-domain experiments.

36 citations

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TL;DR: In this paper, a dipole-dipole Forster mechanism of excitation energy transfer between donor-donor and rhodamine 6G molecules in water with varying pH has been studied by using steady state measurements.
Abstract: Excitation energy transfer between acriflavine (donor) to rhodamine 6G (acceptor) molecules in water with varying pH has been studied by using steady state measurements. From absorption and fluorescence spectra of donor and acceptor, overlap integrals for donor fluorescence and donor absorption ( Ω DD ) as well as donor fluorescence and acceptor absorption ( Ω DA ) have been calculated. The corresponding critical transfer distances for dipole–dipole Forster mechanism of excitation energy transfer between donor–donor ( R 0D ) and donor–acceptor ( R 0A ), reduced concentration and efficiency of energy transfer have also been calculated. It has been found that the Ω DA change with pH whereas Ω DD remain unchanged, resulting in change in energy transfer from donor to acceptor with pH, but no change in energy migration. The efficiency of excitation energy transfer is maximum for a highly basic solution and it decreases with a decrease in pH. The energy transfer efficiency, reduced concentration, and overlap integrals show a linear dependence on pH. It has been proposed that the system may be used as a wide range (1.4 to 12) pH sensor with an accuracy of 0.01.

30 citations

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TL;DR: In this article, the authors studied the energy transfer between acriflavine and erythrosin B dyes in solutions of two different viscosities and found that the observed diffusion coefficients are higher than even the sum of diffusion co-efficient for translational diffusion and energy migration for immobile donors.

27 citations


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425 citations

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TL;DR: The current state of the art in water sensors is described and an overview of the major advances made in this field post 2000 is provided to allow for an expedited process of translation into more widespread application.
Abstract: In this tutorial review, we describe the current state of the art in water sensors and provide an overview of the major advances made in this field post 2000. The field is currently still in its early development stages and subject to continuous improvements, and the current work provides a structured approach describing different sensing mechanisms and potential future applications associated with each of these. With these developments and their potential implications for the diverse scientific fields requiring tight control over the water content, we strongly believe the discipline is potentially at the threshold of translation into more widespread application and we hope the current review might allow for an expedited process thereof.

393 citations

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TL;DR: This Zn-MOF represents an excellent PL water-sensing material, showing a fast and highly selective response to water on a molecular level and resulting in sensitive two-colour photoluminescence switching over cycles.
Abstract: A convenient, fast and selective water analysis method is highly desirable in industrial and detection processes. Here a robust microporous Zn-MOF (metal–organic framework, Zn(hpi2cf)(DMF)(H2O)) is assembled from a dual-emissive H2hpi2cf (5-(2-(5-fluoro-2-hydroxyphenyl)-4,5-bis(4-fluorophenyl)-1H-imidazol-1-yl)isophthalic acid) ligand that exhibits characteristic excited state intramolecular proton transfer (ESIPT). This Zn-MOF contains amphipathic micropores (<3 A) and undergoes extremely facile single-crystal-to-single-crystal transformation driven by reversible removal/uptake of coordinating water molecules simply stimulated by dry gas blowing or gentle heating at 70 °C, manifesting an excellent example of dynamic reversible coordination behaviour. The interconversion between the hydrated and dehydrated phases can turn the ligand ESIPT process on or off, resulting in sensitive two-colour photoluminescence switching over cycles. Therefore, this Zn-MOF represents an excellent PL water-sensing material, showing a fast (on the order of seconds) and highly selective response to water on a molecular level. Furthermore, paper or in situ grown ZnO-based sensing films have been fabricated and applied in humidity sensing (RH<1%), detection of traces of water (<0.05% v/v) in various organic solvents, thermal imaging and as a thermometer. Fast and sensitive detection of water molecules in organic solvents and gases remains an important challenge. Here, Pan and co-workers design a metal-organic framework capable of ultrafast and reversible water sensing by photoluminescence switching via an excited state intramolecular proton transfer mechanism.

374 citations

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TL;DR: In this paper, the DFT + U method was used to predict the structural and electronic properties of transition-metal sulfides formed by 3D transition metal atoms, including magneto-volume effects and magneto structural effects.
Abstract: Density-functional studies of structural and electronic properties of transition-metal sulfides formed by 3d transition metals, based on the local spin-density approximation and including non-local corrections to the exchange–correlation functional (generalized gradient approximation), have demonstrated the importance of magneto-volume effects and magneto-structural effects, but could not achieve full agreement with experiment. A further improvement is to consider electronic correlation effects due to tightly bound and localized d-states on the transition metal atoms. With the DFT + U method used in this work, these correlation effects are taken in account and yield improved predictions for volume, magnetic moment, exchange splitting and bandgap. For MnS the semiconducting gap is correctly predicted, and for MnS2 the high-spin AFM type-III state can be stabilized over the low-spin state. For FeS even weak correlation effects lead to better predictions for the semiconducting gap, volume and magnetic moment.

310 citations

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TL;DR: In this paper, the fluorescence quenching produced by the aggregates of the zwitter-ion and the cationic molecular forms of Rhodamine B in water and in ethanol is evaluated.

204 citations