Browsing by Author "Chandan Upadhyay"

Now showing 1 - 17 of 17

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) Pranjalee Yadav; Rohit Kumar; S. Srikrishna; Anoop Kumar Pandey; Lokman H. Choudhury; Chandan Upadhyay; Vinod P. Singh
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.
Development of cost-effective proton exchange membrane using agro waste-based biochar for application in microbial fuel cell (MFC)
(Springer Science and Business Media Deutschland GmbH, 2025) Amit Bar; Onkar Jaychand Kupkar; Chandan Upadhyay; R. S. Singh
Microbial fuel cell (MFC) is a promising emerging technology in which waste can be converted into energy, hydrogen and many other valuable products. Proton exchange membrane (PEM) contributes a significant portion (around 50%) of the overall cost of MFC. The current study focuses on synthesizing low-cost PEM using biochar produced by biomass pyrolysis at 400 °C. The Pristine biochar (PB) obtained by pyrolysis was sulphonated to improve the desirable properties required for the preparation of PEM. Brunauer-Emmet-Teller (BET) measurements show a considerable improvement in surface area per unit weight and decreased sulphonated biochar (SB) micropore size. FTIR analysis shows that the peak position is at 1169 cm−1, which indicates the presence of the sulphonyl group (-SO3H) in the SB. The presence of the group demonstrated that the sulphonation of biochar by sulphuric acid was done successfully. A comparison of proton conductivity between SB and PB was determined by Nyquist plot using Zsimp Win 3.21 software and the data taken from electrochemical impedance spectroscopy (EIS) measurements. A large improvement in the proton conductivity of SB (0.135 S cm−1) was observed compared to that of PB (0.0204 S cm−1). The morphological structure of PB and SB was studied using the scanning electron microscope (SEM). The SEM results showed more even pore distribution and the presence of pores and crevices on the SB than PB, which promotes better proton transfer. EDX results show the presence of sulphur in SB, which confirms the results of FTIR. Polyvinyl alcohol was used as a binder for the membrane preparation. The maximum power density of the MFC with SB-based PEM was found to be 5.6 mWcm−1. The estimated cost of the material was found to be 17 times cheaper than Nafion. This study demonstrated that biochar-based PEM can drastically lower the MFC’s overall cost. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.
Development of cost-effective proton exchange membrane using agro waste-based biochar for application in microbial fuel cell (MFC)
(Springer Science and Business Media Deutschland GmbH, 2024) Amit Bar; Onkar Jaychand Kupkar; Chandan Upadhyay; R.S. Singh
Microbial fuel cell (MFC) is a promising emerging technology in which waste can be converted into energy, hydrogen and many other valuable products. Proton exchange membrane (PEM) contributes a significant portion (around 50%) of the overall cost of MFC. The current study focuses on synthesizing low-cost PEM using biochar produced by biomass pyrolysis at 400 °C. The Pristine biochar (PB) obtained by pyrolysis was sulphonated to improve the desirable properties required for the preparation of PEM. Brunauer-Emmet-Teller (BET) measurements show a considerable improvement in surface area per unit weight and decreased sulphonated biochar (SB) micropore size. FTIR analysis shows that the peak position is at 1169 cm−1, which indicates the presence of the sulphonyl group (-SO3H) in the SB. The presence of the group demonstrated that the sulphonation of biochar by sulphuric acid was done successfully. A comparison of proton conductivity between SB and PB was determined by Nyquist plot using Zsimp Win 3.21 software and the data taken from electrochemical impedance spectroscopy (EIS) measurements. A large improvement in the proton conductivity of SB (0.135 S cm−1) was observed compared to that of PB (0.0204 S cm−1). The morphological structure of PB and SB was studied using the scanning electron microscope (SEM). The SEM results showed more even pore distribution and the presence of pores and crevices on the SB than PB, which promotes better proton transfer. EDX results show the presence of sulphur in SB, which confirms the results of FTIR. Polyvinyl alcohol was used as a binder for the membrane preparation. The maximum power density of the MFC with SB-based PEM was found to be 5.6 mWcm−1. The estimated cost of the material was found to be 17 times cheaper than Nafion. This study demonstrated that biochar-based PEM can drastically lower the MFC’s overall cost. Graphical abstract: (Figure presented.). © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.
Effect of Mn doping on the electronic and optical properties of Dy2Ti2O7: a combined spectroscopic and theoretical study
(Institute of Physics, 2023) Rajnikant Upadhyay; Manjari Shukla; Rajan K Pandey; Chandan Upadhyay
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.
Emergence of field-induced memory effect in spin ices
(Institute of Physics, 2023) Pramod K Yadav; Rajnikant Upadhyay; Rahul Kumar; Pavan Nukala; Chandan Upadhyay
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.
Evaluation of surface-modified orthodontic wires by different concentration and dipping duration of titanium oxide (TiO 2) nanoparticles
(Wolters Kluwer Medknow Publications, 2023) T.P. Chaturvedi; P. Indumathi; Vipul Kumar Sharma; Ashish Agrawal; Deepak Singh; Chandan Upadhyay
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.
Highly efficient WS2 QD-based non-enzymatic fluorescent biosensor for ofloxacin and ciprofloxacin monitoring in aquatic media
(Royal Society of Chemistry, 2024) Sunayana Bora; Chandan Upadhyay
Quantum dot-based biosensors have gained prominence in recent times for the detection of biological and chemical hazards present in aquatic media which essentially contribute to the degradation of the environment and human health. Within this work, we demonstrate a WS2 QD-induced turn-on fluorescent probe for specific monitoring of ofloxacin (OFL) and ciprofloxacin (CIP) residues in water. An efficient one-pot hydrothermal approach is applied for fluorescent water-soluble WS2 QD preparation. The WS2 QDs possess excellent photostability and monodispersity along with a superior shelf life. The WS2 QDs interacting with FQns (OFL and CIP) showed a systematically enhanced fluorescence in varying FQn concentrations from 0 μM to 3 μM. Also, all the measurements showed excellent results for sensitivity along with superior specificity as well as anti-interference ability over other interfering substances like various metal ions and antibiotic derivatives. The proposed sensor allows the quantification of FQns in the range of 0-3 μM with the lowest detectable amount (LOD) of 0.08 μM and 0.06 μM and the minimal limit of quantification (LOQ) of 0.26 μM and 0.21 μM for both OFL and CIP, respectively, at natural pH. It achieved higher sensitivity than many established techniques and materials making up the gap of other existing systems in this range. We observed excellent results for the rapid in situ detection of FQns by implementing WS2 QDs. The findings show potential for future use in real-time applications for FQns. © 2024 RSC.
Impact of Eu3 +/Y3+ doping on the structural and optical properties of SrTiO3 perovskite phosphor and multi-functional applications
(Elsevier Ltd, 2025) Satyam Upadhyay; Arpita Dwivedi; Prateek Kumar Yadav; Monika Srivastava; Amit Kumar Srivastava; Chandan Upadhyay; Sanjay Kumar Srivastava
A latent fingerprint (LFP) examination is essential for identifying fingerprints at crime sites, and personal data for legal operations requires economical, eco-friendly, and sensitive new materials. Here, a new composition of intense red-emitting Eu3+ and Y3+ co-doped SrTiO3 perovskites nanophosphor synthesized using a modified sol-gel-assisted combustion technique has been reported. To explore the structural and optical features of the nanophosphors the samples are characterized by various techniques. The powder XRD pattern reveals that the approximate crystallite size is 30 nm, which is consistent with TEM. It is found that with the mid- and near-ultraviolet light excitation, Eu3+ and Y3+ co-doped SrTiO3 nanophosphor displays a strong red emission at 618 nm for optimal concentrations (3 mol% Eu). The CIE (0.656, 0.344), color purity 95 %, CRI 98 %, and CCT values 2435 K, which is less than 5000 K reveals that the Eu3+ and Y3+ co-doped SrTiO3 phosphor was highly useful for the fabrication of warm LED and display device applications. Further, the optimized phosphor was tested (under UV light of 254 nm) for the visualization of LFP and security ink on various material surfaces. The results demonstrated that it provides an effective method for visualizing ridge patterns, offering a promising approach for applications in these areas. Based on the findings, Eu3+ and Y3+ co-doped SrTiO3 show potential for various optoelectronic applications, including WLEDs, LFP detection, security inks, and LEDs. © 2025 Elsevier B.V.
Influence of local defects in the generation of memory effect in Dy2Ti2O7 compound: Fe-doped study
(Institute of Physics, 2024) Pramod K. Yadav; Rajnikant Upadhyay; Rahul Kumar; Pavan Nukala; Chandan Upadhyay
The study of defect-induced effects in functional materials is high-priority research for the miniaturization of smart devices. To elucidate the influence of local defects stemming from intrinsic or extrinsic factors on the enigmatic behavior of cooperative spin dynamics, we investigated the Dy2-xFexTi2O7 compound within a narrow Fe substitution range (x = 0-0.15). Our experimental findings unequivocally demonstrate that the dynamic response of cooperative spins and the emergence of anomalous memory effect are intricately linked to local defects. Depending on the nature and dynamics of these defects, the dynamic response of cooperative spins undergoes alteration. Notably, observed anomalous effect becomes more pronounced in scenarios characterized by slower defect dynamics and when cooperative spins are further from equilibrium. The emergence and sensitivity of thermomagnetic hysteresis (memory effect) to cooperative spin dynamics and external stimuli underscore the richness of Dy2Ti2O7 as a material for captivating physics investigations. © 2024 IOP Publishing Ltd.
Metallurgical study of copper objects from the Varanasi region, India (1200 BCE to 400 CE)
(John Wiley and Sons Inc, 2025) Prabhakar Upadhyay; Rajalakshmi Sivarajan; Vibha Tripathi; Chandan Upadhyay
This study aims to investigate ancient Indian copper metallurgy based on selected copper artifacts recovered from India. The collected objects belong to the period c. 1200 BCE to 400 CE. The paper discusses the analysis of seven artifacts from two archaeological sites (Agiabir and Raipura) around the Varanasi region in Northern India. The study explores the manufacturing techniques and alloying practices applied to the artifacts by analyzing the excavated objects using optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray fluorescence spectroscopy. The microstructure of the artifacts revealed the practice of annealing, casting, and forging. Elemental analysis of these objects shows that most of the artifacts are copper–tin alloys, having varying amounts of tin. This study indicates that the tin amount has been varied according to the object's functionality. © 2024 The Author(s). Archaeometry © 2024 University of Oxford.
Metallurgical study of copper objects from the Varanasi region, India (1200 BCE to 400 CE)
(John Wiley and Sons Inc, 2024) Prabhakar Upadhyay; Rajalakshmi Sivarajan; Vibha Tripathi; Chandan Upadhyay
This study aims to investigate ancient Indian copper metallurgy based on selected copper artifacts recovered from India. The collected objects belong to the period c. 1200 BCE to 400 CE. The paper discusses the analysis of seven artifacts from two archaeological sites (Agiabir and Raipura) around the Varanasi region in Northern India. The study explores the manufacturing techniques and alloying practices applied to the artifacts by analyzing the excavated objects using optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray fluorescence spectroscopy. The microstructure of the artifacts revealed the practice of annealing, casting, and forging. Elemental analysis of these objects shows that most of the artifacts are copper–tin alloys, having varying amounts of tin. This study indicates that the tin amount has been varied according to the object's functionality. © 2024 The Author(s). Archaeometry © 2024 University of Oxford.
Nanoparticle-mediated defense priming: A review of strategies for enhancing plant resilience against biotic and abiotic stresses
(Elsevier Masson s.r.l., 2024) Nidhi Yadav; Sunayana Bora; Bandana Devi; Chandan Upadhyay; Prashant Singh
Nanotechnology has emerged as a promising field with the potential to revolutionize agriculture, particularly in enhancing plant defense mechanisms. Nanoparticles (NPs) are instrumental in plant defense priming, where plants are pre-exposed to controlled levels of stress to heighten their alertness and responsiveness to subsequent stressors. This process improves overall plant performance by enabling quicker and more effective responses to secondary stimuli. This review explores the application of NPs as priming agents, utilizing their unique physicochemical properties to bolster plants' innate defense mechanisms. It discusses key findings in NP-based plant defense priming, including various NP types such as metallic, metal oxide, and carbon-based NPs. The review also investigates the intricate mechanisms by which NPs interact with plants, including uptake, translocation, and their effects on plant physiology, morphology, and molecular processes. Additionally, the review examines how NPs can enhance plant responses to a range of stressors, from pathogen attacks and herbivore infestations to environmental stresses. It also discusses NPs' ability to improve plants' tolerance to abiotic stresses like drought, salinity, and heavy metals. Safety and regulatory aspects of NP use in agriculture are thoroughly addressed, emphasizing responsible and ethical deployment for environmental and human health safety. By harnessing the potential of NPs, this approach shows promise in reducing crop losses, increasing yields, and enhancing global food security while minimizing the environmental impact of traditional agricultural practices. The review concludes by emphasizing the importance of ongoing research to optimize NP formulations, dosages, and delivery methods for practical application in diverse agricultural settings. © 2024 Elsevier Masson SAS
Photoluminescence behaviour of a stimuli responsive Schiff base: Aggregation induced emission and piezochromism
(Elsevier Ltd, 2019) Pranjalee Yadav; Ashish Kumar Singh; Chandan Upadhyay; Vinod P. Singh
A naphthaldehyde based Schiff base, HMP has been synthesized by simple one-pot synthesis and characterized by IR, NMR and mass spectral techniques. HMP was non-emissive in acetonitrile, but its emission intensity was enhanced drastically (68 folds) upon addition of water, demonstrating typical aggregation induced emission (AIE) behaviour. Fluorescence quantum yield was increased drastically on aggregation from 0.3% (fw = 0%) to 8.1% (fw = 99%). Lifetime decay measurements were also performed in support of AIE property. Single crystal X-ray diffraction and DFT studies reveal that conformational transformation from benzenoid to quinonoid form induces restricted intramoleclar rotation (RIR) which contributes to AIE property. HMP was found to exhibit strong luminescence and piezochromism in solid state. Interestingly, dark yellow luminescence of crystalline HMP was changed to light green in response to grinding and a blue shift from 544 nm to 531 nm was observed. HMP exhibits good parent crystalline maintenance capability during grinding. Synthetic ease and reversible transformation of HMP are the key features to establish its application in pressjet printing and pressure sensing. © 2018 Elsevier Ltd
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) Namrata Joshi; Manoj Kumar Dash; Chandan Upadhyay; Vikas Jindal; Pradip Kumar Panda; Manjari Shukla
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
Surface plasmon coupled metal enhanced spectral and charge transport properties of poly(3,3′′′-dialkylquarterthiophene) Langmuir Schaefer films
(Royal Society of Chemistry, 2015) Rajiv K. Pandey; Swatantra K. Yadav; Chandan Upadhyay; Rajiv Prakash; Hirdyesh Mishra
The coupling of organic molecule excitons with metal nano-structure surface plasmons can improve the performance of optoelectronic devices. This paper presents the effect of localized silver metal surface plasmons on spectral as well as charge transport properties of ordered molecular Langmuir Schaefer (LS) films of a fluorescent conducting multifunctional organic polymer: poly (3,3′′′-dialkylquarterthiophene) [PQT-12]. The stability and thickness of the PQT-12 LS film were studied by the pressure vs. area isotherm curve. Atomic force microscopy images indicate the formation of a smooth ordered polymer thin LS film of PQT-12 over silver nanostructure island films [SNIF] (∼40 to 50 nm in size). Raman, electronic absorption and fluorescence spectral measurements of the PQT-12 LS film, near SNIF i.e. the near field, show a plasmon coupled enhancement of ∼13 fold in the intensity of Raman bands along with a two-fold enhancement in the absorption band (531 nm) and a six-fold enhancement in the fluorescence band (665 nm) coupled with a decrease in fluorescence decay time with improved photostability as compared to an identical control sample containing no SNIF i.e. the far field condition. These results indicate the formation of a plasmon coupled unified fluorophore system due to adsorption of the PQT-12 LS film over SNIF. The effect of plasmonic coupling is also studied by applying an electric field in sandwiched structures of Al/PQT-12 LS/SNIF/ITO with respect to Al/PQT-12 LS/ITO. Nearly three orders of magnitude enhancement in the current density (J-V plot) of the PQT-12 LS film is observed in the presence of SNIF, which further increases, on illuminating the film by green laser light [532 nm], while the fluorescence intensity and decay time decrease. X-ray photoelectron spectroscopic measurements of SNIF also show a red shift in 3d3/2 and 3d5/2 transitions of silver in the PQT-12 coated LS film, which indicates partial charge transfer from the PQT-12 polymer backbone to SNIF and causes an enhancement in conductivity. This again supports the formation of a field controlled radiating plasmon coupled fluorophore unified system. These findings show greater potential in developing a voltage controlled high photon flux electroluminescent material for multifarious applications. This journal is © The Royal Society of Chemistry.
Tunable photoluminescence and energy transfer of Eu3+,Ho3+-doped Ca0.05Y1.93-xO2 nanophosphors for warm white LEDs applications
(Nature Research, 2022) Arpita Dwivedi; Monika Srivastava; Amit Srivastava; Chandan Upadhyay; Sanjay Kumar Srivastava
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 Å. 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).
Urease Immobilized Fluorescent Gold Nanoparticles for Urea Sensing
(Humana Press Inc., 2015) Upendra Kumar Parashar; Narsingh R. Nirala; Chandan Upadhyay; P.S. Saxena; Anchal Srivastava
We report a surfactant-free synthesis of monodispersed gold nanoparticles (AuNPs) with average size of 15 nm. An approach for visual and fluorescent sensing of urea in aqueous solution based on shift in surface plasmon band (SPB) maxima as well as quench in fluorescence intensity. To enable the urea detection, we functionalized the thiol-capped gold nanoparticles with urease, the enzyme specific to urea using carbodiimide chemistry. The visible color changed of the gold colloidal solution from red to blue (or purple); this was evident from quenching in absorbance and fluorescence intensity, is the principle applied here for the sensing of urea. The solution turns blue when the urea concentration exceeds 8 mg/dL which reveals visual lower detection limit. The lower detection limits governed by the fluorescence quenching were found 5 mg/dL (R2 = 0.99) which is highly sensitive and selective compared to shift in SPB maxima. The approach depicted here seems to be important in clinical diagnosis. © 2015, Springer Science+Business Media New York.