Browsing by Author "Upadhyay, Chandan"

Now showing 1 - 6 of 6
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    A reversible and efficient probe for dual mode recognition of Al3+ and Cu2+ with logic gate behaviour: Crystal structure, theoretical and in-vivo bio-imaging investigations
    (Elsevier B.V., 2022) Yadav, Pranjalee; Kumar, Rohit; Srikrishna, S.; Kumar Pandey, Anoop; Choudhury, Lokman H.; Upadhyay, Chandan; Singh, Vinod P.
    This work presents the synthesis, characterization, crystal structure and spectroscopic investigations of isophthalohydrazide based probe. Among various tested metal ions, the probe selectively detects Al3+ and Cu2+ in aqueous ethanol via fluorometric and colorimetric methods, respectively. It displays a fluorescence �turn-on� response with Al3+ and visual colour change from colourless to yellow with Cu2+. Sensing mechanism is explored with UV�Vis, fluorescence spectroscopy and 1H NMR titration, and confirmed with computational results. Suppression of C[dbnd]N isomerization and photo-induced electron transfer (PET) along with chelation enhanced fluorescence emission (CHEF) result in �turn-on� fluorescence with Al3+ while ligand to metal charge transfer (LMCT) accounts for visual colour change with Cu2+. Job's plot and HRMS confirm 1:2 (L:M) stoichiometry. The probe also exhibits efficient reversibility and reproducibility with EDTA which are successfully mimicked with combinatorial logic gate and truth table. Additionally, solid state applications and bio-imaging investigation on gut tissue of Drosophila 3rd instar larvae are performed. � 2021 Elsevier B.V.
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    Effect of Mn doping on the electronic and optical properties of Dy2Ti2O7: a combined spectroscopic and theoretical study
    (Institute of Physics, 2023) Upadhyay, Rajnikant; Shukla, Manjari; Pandey, Rajan K; Upadhyay, Chandan
    Electronic and optical studies on Dy2Ti2?Mn x O7 (x = 0.00, 0.05, 0.10, 0.15, & 0.20) have been presented through both, theoretical (density functional theory (DFT) calculations) and experimental (ultraviolet-visible absorption and photoluminescence emission spectroscopy) approaches. DFT calculations were employed considering the local density approximation (LDA) and LDA-1/2 for exchange-correlation interactions. Computed crystallographic parameters and energy band-gap using theoretical formulations are in good agreement with experimental results. The band-gap value obtained through the LDA-1/2 approach indicates insulated ground state of Dy2Ti2?xMn x O7 (x = 0.00, 0.05, 0.10, 0.15, 0.20) system. Experimentally obtained band gap value reduces from 3.82 eV to 2.45 eV with increase in positive chemical pressure as x increases from 0 to 0.20. Reduction in band gap value is attributed to the fact that there exists a lack of hybridization between the O-2p orbital and Ti-3d orbital, which is well correlated with the crystallographic data. Jahn-Teller effect is likely to be responsible for the presence of a mixed state of Mn (explained using x-ray photoelectron spectroscopy results), resulting in the intermediate Mn state between the valence band and the conduction band with immediate inclusion of Mn at Ti site in Dy2Ti2?x Mn x O7 system. � 2023 IOP Publishing Ltd.
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    Emergence of field-induced memory effect in spin ices
    (Institute of Physics, 2023) Yadav, Pramod K; Upadhyay, Rajnikant; Kumar, Rahul; Nukala, Pavan; Upadhyay, Chandan
    Out-of-equilibrium investigation of strongly correlated materials deciphers the hidden equilibrium properties. Herein, we have investigated the out-of-equilibrium magnetic properties of polycrystalline Dy2Ti2O7 and Ho2Ti2O7 spin ices. Our experimental findings reveal the emergence of magnetic field-induced anomalous hysteresis observed solely in temperature-and magnetic field-dependent AC susceptibility measurements. The observed memory effect (anomalous thermomagnetic hysteresis) exhibits a strong dependence on both thermal and non-thermal driving variables. Owing to the non-collinear spin structure, the applied DC bias magnetic field produces quenched disorder sites in the cooperative Ising spin matrix and suppresses the spin-phonon coupling. These quench disorders create a dynamic spin correlation, having slow spin relaxation and quick decay time, which additionally contribute to AC susceptibility. The initial conditions and measurement protocol decide the magnitude and sign of this dynamical term contributing to AC susceptibility. It is being suggested that such out-of-equilibrium properties arise from the combined influences of geometric frustration, disorder, and the cooperative nature of spin dynamics exhibited by these materials. � 2023 IOP Publishing Ltd.
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    Evaluation of surface-modified orthodontic wires by different concentration and dipping duration of titanium oxide (TiO 2) nanoparticles
    (Wolters Kluwer Medknow Publications, 2023) Chaturvedi, T.P.; Indumathi, P.; Sharma, Vipul Kumar; Agrawal, Ashish; Singh, Deepak; Upadhyay, Chandan
    OBJECTIVE: To evaluate in-vitro surface characteristics and frictional properties of orthodontic stainless steel and beta-titanium archwires after surface modification with different concentrations and coating time of titanium oxide (TiO 2) nanoparticles by Sol-gel dip coating method. MATERIALS AND METHODS: The experiment was carried out with 4 different concentrations (1:2, 1:4, 1:6, and 1:8) and three different dipping durations (24 hours, 48 hours, and 72 hours) over ten main test groups of SS and TMA archwires with uncoated wires acting as control in both dry and wet conditions. Phase analysis and surface characterization of TiO 2 was analyzed by X-ray Diffractometry, surface evaluation with the help of scanning electron microscopy (SEM), and frictional characteristics were evaluated. RESULTS: Among all the concentrations 1:6 ratio with 48 hours of dipping duration showed better surface characteristics. A statistically significant difference in frictional coefficient was observed in both SS and TMA wires than their respective controls (p = 0.001). Intragroup comparison among SS and TMA groups showed that groups with 1:6 ratio and 48 hours dipping duration had least frictional coefficient in both dry and wet conditions (p = 0.001). Intergroup comparison between SS and TMA showed that SS group had significantly reduced friction than TMA (p = 0.001) except in few groups. CONCLUSION: TiO 2 nanoparticle with a concentration ratio of 1:6 and 48 hours dipping duration is recommended for surface modification of orthodontic archwires. � 2023 Wolters Kluwer Medknow Publications. All rights reserved.
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    Physico-chemical characterization of kajjali, black sulphide of mercury, with respect to the role of sulfur in its formation and structure
    (Elsevier B.V., 2021) Joshi, Namrata; Dash, Manoj Kumar; Upadhyay, Chandan; Jindal, Vikas; Panda, Pradip Kumar; Shukla, Manjari
    Background: Kajjali is used as a base for Ayurvedic herbo-mineral medicines. It is a combination of mercury with sulfur in varying proportions. The ratio of sulfur (S) added to mercury (Hg) directly relates to the therapeutic efficacy of the compound. Objective: To analyze the physico-chemical characteristics of samaguna gandhaka kajjali (Hg: S = 1:1) and shadaguna gandhaka kajjali (Hg: S = 1:6). Materials and methods: X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Fourier transmission infrared spectroscopy, thermo-gravimetry analysis, and atomic absorption spectroscopy were applied to characterize each type of kajjali. Results: It was found that the particle size of the formed kajjali compound increases with a decrease in the mercury to sulfur ratio. The presence of excess sulfur does not change the surface oxidation states as revealed by the XPS analysis. No trace of mercury has been found in both samaguna gandhaka kajjali (SGK-1) and shadguna gandhaka kajjali (SGK-6), indicating a complete Hg reaction with S. Conclusion: Kajjali simulates nanomaterial of the modern era and possesses therapeutic efficacy as mentioned in classical Ayurveda texts. Complete trituration of mercury and sulfur combination ends up with this kajjali formation incorporating the potency of nanotherapeutics. � 2021 The Authors
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    Tunable photoluminescence and energy transfer of Eu3+,Ho3+-doped Ca0.05Y1.93-xO2 nanophosphors for warm white LEDs applications
    (Nature Research, 2022) Dwivedi, Arpita; Srivastava, Monika; Srivastava, Amit; Upadhyay, Chandan; Srivastava, Sanjay Kumar
    A series of Eu3+ ions doped Ca0.05Y1.93-xO3:0.02Ho3+ (CYO:Ho3+,xEu3+) nanophosphors having multicolour tuneability have been synthesised by following a simplistic solution combustion approach. The synthesised samples have been characterised by employing X-ray diffraction (XRD), Transmission electron microscope (TEM), and Fourier transforms infrared spectroscopy (FTIR). The optical properties have been engrossed by UV�visible and photoluminescent excitation and emission spectra, and decay lifetimes measurements. The characteristic emission, which occurs due to the f-f transition of Ho3+ and Eu3+ has been observed in emission spectra with excitation of 448�nm. By adjusting the doping ratio of Ho3+/Eu3+, the as-synthesized nanophosphor accomplishes multicolour tunability from green-yellow to red. Emission spectra and decay lifetime curve recommend dipole�dipole interaction causes energy transfer from Ho3+ ? Eu3+. The energy transfer process from Ho3+ to Eu3+ has been confirmed through electric dipole�dipole interaction with critical distance 15.146��. Moreover, temperature dependent emission spectra show the high thermal stability with an activation energy ? 0.21�eV, with the quantum efficiency of 83.6%. CIE coordinate illustrates that the singly doped Ho3+ and Eu3+ lie in the green and red region, respectively, while the as-synthesized CYO:Ho3+,xEu3+shows tunability from green to red with low CCT and high colour purity values. Hence, the CYO:Ho3+,xEu3+nanophosphor may be a near-UV excited multicolour colour-tunable pertinent candidate with potential prospects for multicolour- display and near-ultraviolet lighting applications. � 2022, The Author(s).