Publications by authors named "Vikas Dubey"

21 Publications

  • Page 1 of 1

White light emission and thermoluminescence studies of Dy activated Hardystonite (Ca ZnSi O ) phosphor.

Luminescence 2021 May 28. Epub 2021 May 28.

Department of Physics, Govt. V.Y.T.PG. Auto. College Durg, C.G., India.

Herein, we have reported the photoluminescent and thermoluminescent properties of Dy activated Ca ZnSi O phosphors synthesized via the solid-state method. The synthesized phosphors showed hardystonite type structure, and had micron sized particles. Fourier transform infrared spectroscopy (FTIR) showed the existence of the functional groups and confirmed the formation of phosphor and photoluminescent techniques. The phosphors under excitation at 239 nm exhibited green-yellow emission spectra in the region of 481-575 nm corresponding to the F → H and F → H transitions of Dy ions. The Commission Internationale de l'Eclairage (CIE) coordinates were achieved to be (0.25, 0.27), which was narrowly close to the white region. Thermoluminescence (TL) glow curve analysis of prepared Dy -activated Ca ZnSi O phosphors were recorded for different UV exposure time and found linear response with dose. The TL glow curves, recorded with various UV exposure time ranging from 5 to 25 min, showed linear response with dosage. The corresponding kinetic parameters were also calculated using Computerized Glow Curve Deconvolution (CGCD) technique. Activation energy was observed to enhance with the increase of the peak temperature and its value was substantially high for the third peak fitted by CGCD. The obtained results indicated that the synthesized pristine phosphors could be potential for lighting, displays and dosimetric applications.
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http://dx.doi.org/10.1002/bio.4095DOI Listing
May 2021

An Intracellular Pathway Controlled by the N-terminus of the Pump Subunit Inhibits the Bacterial KdpFABC Ion Pump in High K Conditions.

J Mol Biol 2021 May 2;433(15):167008. Epub 2021 May 2.

PHYLIFE: Physical Life Science, Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, Odense 5230 M, Denmark. Electronic address:

The heterotetrameric bacterial KdpFABC transmembrane protein complex is an ion channel-pump hybrid that consumes ATP to import K against its transmembrane chemical potential gradient in low external K environments. The KdpB ion-pump subunit of KdpFABC is a P-type ATPase, and catalyses ATP hydrolysis. Under high external K conditions, K can diffuse into the cells through passive ion channels. KdpFABC must therefore be inhibited in high K conditions to conserve cellular ATP. Inhibition is thought to occur via unusual phosphorylation of residue Ser162 of the TGES motif of the cytoplasmic A domain. It is proposed that phosphorylation most likely traps KdpB in an inactive E1-P like conformation, but the molecular mechanism of phosphorylation-mediated inhibition remains unknown. Here, we employ molecular dynamics (MD) simulations of the dephosphorylated and phosphorylated versions of KdpFABC to demonstrate that phosphorylated KdpB is trapped in a conformation where the ion-binding site is hydrated by an intracellular pathway between transmembrane helices M1 and M2 which opens in response to the rearrangement of cytoplasmic domains resulting from phosphorylation. Cytoplasmic access of water to the ion-binding site is accompanied by a remarkable loss of secondary structure of the KdpB N-terminus and disruption of a key salt bridge between Glu87 in the A domain and Arg212 in the P domain. Our results provide the molecular basis of a unique mechanism of regulation amongst P-type ATPases, and suggest that the N-terminus has a significant role to play in the conformational cycle and regulation of KdpFABC.
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http://dx.doi.org/10.1016/j.jmb.2021.167008DOI Listing
May 2021

Breakdown of the Stokes-Einstein Relation in Supercooled Water/Methanol Binary Mixtures: Explanation Using the Translational Jump-Diffusion Approach.

J Phys Chem B 2020 Nov 5;124(46):10398-10408. Epub 2020 Nov 5.

Department of Chemistry, Indian Institute of Technology Patna, Patna, Bihar 801106, India.

A recent experiment has directly checked the validity of the Stokes-Einstein (SE) relation for pure water, pure methanol, and their binary mixtures of three different compositions at different temperatures. The effect of composition on the nature of breakdown of the SE relation is interesting. While in the majority of the systems, an increasing SE breakdown is observed with decreasing temperature, the breakdown is already significant at higher temperatures for the equimolar mixture. Violations of the SE relation in pure supercooled water at different temperatures and pressures have been previously explained using the translational jump-diffusion (TJD) approach, which provides a fundamental molecular basis, by directly connecting the SE breakdown with jump-diffusion of the molecules. We have used the same TJD approach for explaining the SE breakdown for the methanol/water binary mixtures of compositions studied in the experiment over a wide range of temperatures between 220 K and 300 K. We have understood that the jump-diffusion is the key responsible factor for the SE breakdown. The maximum jump-diffusion contribution gives rise to the early SE breakdown observed for the equimolar mixture observed in the experiment. This study, therefore, provides molecular insight into the SE breakdown for the supercooled water/methanol binary mixture, as found in the experiment.
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http://dx.doi.org/10.1021/acs.jpcb.0c07318DOI Listing
November 2020

Cholesterol binding to the sterol-sensing region of Niemann Pick C1 protein confines dynamics of its N-terminal domain.

PLoS Comput Biol 2020 10 6;16(10):e1007554. Epub 2020 Oct 6.

PhyLife Physical Life Sciences, Department of Physics Chemistry, and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark.

Lysosomal accumulation of cholesterol is a hallmark of Niemann Pick type C (NPC) disease caused by mutations primarily in the lysosomal membrane protein NPC1. NPC1 contains a transmembrane sterol-sensing domain (SSD), which is supposed to regulate protein activity upon cholesterol binding, but the mechanisms underlying this process are poorly understood. Using atomistic simulations, we show that in the absence of cholesterol in the SSD, the luminal domains of NPC1 are highly dynamic, resulting in the disengagement of the NTD from the rest of the protein. The disengaged NPC1 adopts a flexed conformation that approaches the lipid bilayer, and could represent a conformational state primed to receive a sterol molecule from the soluble lysosomal cholesterol carrier NPC2. The binding of cholesterol to the SSD of NPC1 allosterically suppresses the conformational dynamics of the luminal domains resulting in an upright NTD conformation. The presence of an additional 20% cholesterol in the membrane has negligible impact on this process. The additional presence of an NTD-bound cholesterol suppresses the flexing of the NTD. We propose that cholesterol acts as an allosteric effector, and the modulation of NTD dynamics by the SSD-bound cholesterol constitutes an allosteric feedback mechanism in NPC1 that controls cholesterol abundance in the lysosomal membrane.
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http://dx.doi.org/10.1371/journal.pcbi.1007554DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7537887PMC
October 2020

Serine phosphorylation regulates the P-type potassium pump KdpFABC.

Elife 2020 09 21;9. Epub 2020 Sep 21.

Skirball Institute, Dept. of Cell Biology, New York University School of Medicine, New York, United States.

KdpFABC is an ATP-dependent K pump that ensures bacterial survival in K-deficient environments. Whereas transcriptional activation of kdpFABC expression is well studied, a mechanism for down-regulation when K levels are restored has not been described. Here, we show that KdpFABC is inhibited when cells return to a K-rich environment. The mechanism of inhibition involves phosphorylation of Ser162 on KdpB, which can be reversed in vitro by treatment with serine phosphatase. Mutating Ser162 to Alanine produces constitutive activity, whereas the phosphomimetic Ser162Asp mutation inactivates the pump. Analyses of the transport cycle show that serine phosphorylation abolishes the K-dependence of ATP hydrolysis and blocks the catalytic cycle after formation of the aspartyl phosphate intermediate (E1~P). This regulatory mechanism is unique amongst P-type pumps and this study furthers our understanding of how bacteria control potassium homeostasis to maintain cell volume and osmotic potential.
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http://dx.doi.org/10.7554/eLife.55480DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7535926PMC
September 2020

Thermoluminescence Studies of β and γ-Irradiated Geological Materials for Environment Monitoring.

J Fluoresc 2020 Jul 20;30(4):819-825. Epub 2020 May 20.

Department of Physics, Govt. V.Y.T.PG. Auto. College, Durg, 491001, India.

In the present report, thermally stimulated luminescence (TSL) of quartz and limestone samples irradiated with β and γ-rays has been investigated. Herein the formation of trap depths and calculation of kinetic parameters of β and γ - irradiated quartz and limestone samples were studied through thermoluminescence (TL) glow curve analyses. The quartz and limestone samples were collected from various sites of Chhattisgarh (Patharia and Dalli-Rajhara mines). The collected raw samples were annealed at 400 °C. The phase formation of collected samples is confirmed by X-ray diffraction studies. The grain sizes of the samples are determined by using Debye-Scherrer formula. TL glow curves of the collected samples were recorded for various doses of β and γ-rays. Kinetic parameters such as order of kinetics frequency factor and trap depth were calculated by employing CGCD methods. A comparative study on the TL properties of the geological materials under β and γ-irradiation was done. The trap model analysis was executed to determine the nature of traps responsible for dominant TL peaks of β and γ-irradiated limestone and quartz samples.
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http://dx.doi.org/10.1007/s10895-020-02536-9DOI Listing
July 2020

Understanding the Origin of the Breakdown of the Stokes-Einstein Relation in Supercooled Water at Different Temperature-Pressure Conditions.

J Phys Chem B 2019 Nov 18;123(47):10089-10099. Epub 2019 Nov 18.

Department of Chemistry , Indian Institute of Technology Patna , Patna , Bihar 801106 , India.

A recent experiment has measured the viscosity of water down to approximately 244 K and up to 300 MPa. The correct viscosity and translational diffusivity data at various temperature-pressure (-) state points allowed for checking the validity of the Stokes-Einstein (SE) relation, which accounts for the coupling between translational self-diffusion and medium viscosity. The diffusion-viscosity decoupling increases with decreasing temperature, but the increasing pressure reduces the extent of the decoupling. Earlier simulation studies explained the breakdown of the SE relation in terms of the location of the Widom line, emanating from the liquid-liquid critical point (LLCP). Although these studies made a significant contribution to the current understanding of the above phenomena, a detailed molecular picture is still lacking. Recently, our group has explained the diffusion-viscosity decoupling from a jump-diffusion perspective. The jump-diffusion coefficient, emanating from the jump translation of water molecules, is calculated using a quantitative approach for different temperatures at ambient pressure. It has been observed that jump-diffusion is the key factor for diffusion-viscosity decoupling in supercooled water. The same method is adopted in the present work to estimate the jump-diffusion coefficient for different - state points and, thereby, explains the role of jump-diffusion for the different extents of the SE relation breakdown at different pressures. The residual diffusion coefficient, the other component of the total diffusion that originates from small step displacement and that is calculated by subtracting the jump-diffusion coefficient from the total diffusion, is seen to be fairly coupled to the viscosity at the entire range of temperature and pressure. Furthermore, we have calculated the average number of H-bonds per water molecule and the tetrahedral order for different - state points and investigated an approximate correlation between the average local structure and the contribution of the jump-diffusion to the total diffusion of water. This study, therefore, puts forward a new perspective for explaining the SE relation breakdown in supercooled water under different pressure conditions.
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http://dx.doi.org/10.1021/acs.jpcb.9b08309DOI Listing
November 2019

A single K-binding site in the crystal structure of the gastric proton pump.

Elife 2019 08 22;8. Epub 2019 Aug 22.

Cellular and Structural Physiology Institute, Nagoya University, Nagoya, Japan.

The gastric proton pump (H,K-ATPase), a P-type ATPase responsible for gastric acidification, mediates electro-neutral exchange of H and K coupled with ATP hydrolysis, but with an as yet undetermined transport stoichiometry. Here we show crystal structures at a resolution of 2.5 Å of the pump in the E2-P transition state, in which the counter-transporting cation is occluded. We found a single K bound to the cation-binding site of the H,K-ATPase, indicating an exchange of 1H/1K per hydrolysis of one ATP molecule. This fulfills the energy requirement for the generation of a six pH unit gradient across the membrane. The structural basis of K recognition is resolved and supported by molecular dynamics simulations, establishing how the H,K-ATPase overcomes the energetic challenge to generate an H gradient of more than a million-fold-one of the highest cation gradients known in mammalian tissue-across the membrane.
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http://dx.doi.org/10.7554/eLife.47701DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6706254PMC
August 2019

Decoupling of Translational Diffusion from the Viscosity of Supercooled Water: Role of Translational Jump Diffusion.

J Phys Chem B 2019 08 13;123(33):7178-7189. Epub 2019 Aug 13.

Department of Chemistry , Indian Institute of Technology Patna , Bihar 801106 , India.

Some experiments have witnessed gradual decoupling of viscosity from the translational self-diffusion of supercooled water with decreasing temperature. This indicates the breakdown of the Stokes-Einstein equation in supercooled water. While some theoretical and computer simulation studies indicated the jump translation of the molecules as a probable origin of the above decoupling, direct quantitative evidence is still lacking. Through a molecular dynamics (MD) simulation study, along with careful consideration of translational jump motion, we have found the most definite proof of increasing relevance of translational jump diffusion in the above decoupling phenomena. By separating the jump-only diffusion contribution from the overall diffusion of the water, we obtain the residual diffusion coefficient, which remains strongly coupled to the viscosity of the medium at the supercooled regime. These new findings can help to elucidate many experimental studies featuring molecular transport properties, where strong diffusion-viscosity decoupling is present.
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http://dx.doi.org/10.1021/acs.jpcb.9b01719DOI Listing
August 2019

Influence of glycerol on the cooling effect of pair hydrophobicity in water: relevance to proteins' stabilization at low temperature.

Phys Chem Chem Phys 2019 Jan;21(2):800-812

Department of Chemistry, Indian Institute of Technology Patna, Bihar 801106, India.

Glycerol, as a cosolvent of water, stabilizes proteins under extreme conditions (both at high and low temperatures). However, the mechanism of stabilization of proteins by glycerol at low temperature is still elusive. Because the decrease of hydrophobic interactions at a lower temperature is one of the crucial factors for the cold denaturation, we ask here whether glycerol protects the hydrophobic interactions upon cooling and thereby acts against cold denaturation. Here, we have performed potential of mean force (PMF) calculations, using the umbrella sampling technique, between a pair of methane hydrophobic solute molecules either in pure water or in binary mixtures of water and glycerol for two different compositions and each of them at four different temperatures. We have found that glycerol increases the pair hydrophobic interaction at all the temperatures studied and that the enhancement is more prominent at the lower temperatures studied here. Decomposition of the PMF into the enthalpic and the entropic components and detailed molecular structural analyses give insight into the above observation. We have found that the enhancement of the hydrophobic interaction with increasing glycerol concentration occurs primarily due to the strengthening of the glycerol-water interaction near the associated methane solute molecule pair and the tetrahedral ordering of the H-bonding network being made uniform around the solute by the added glycerol molecules. These results indirectly justify the efficacy of glycerol for the preservation of proteins against cold denaturation at low temperature.
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http://dx.doi.org/10.1039/c8cp06513fDOI Listing
January 2019

K binding and proton redistribution in the EP state of the H, K-ATPase.

Sci Rep 2018 08 24;8(1):12732. Epub 2018 Aug 24.

Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, 5230 M, Denmark.

The H, K-ATPase (HKA) uses ATP to pump protons into the gastric lumen against a million-fold proton concentration gradient while counter-transporting K from the lumen. The mechanism of release of a proton into a highly acidic stomach environment, and the subsequent binding of a K ion necessitates a network of protonable residues and dynamically changing protonation states in the cation binding pocket dominated by five acidic amino acid residues E343, E795, E820, D824, and D942. We perform molecular dynamics simulations of spontaneous K binding to all possible protonation combinations of the acidic amino acids and carry out free energy calculations to determine the optimal protonation state of the luminal-open EP state of the pump which is ready to bind luminal K. A dynamic pK correlation analysis reveals the likelihood of proton transfer events within the cation binding pocket. In agreement with in-vitro measurements, we find that E795 is likely to be protonated, and that E820 is at the center of the proton transfer network in the luminal-open EP state. The acidic residues D942 and D824 are likely to remain protonated, and the proton redistribution occurs predominantly amongst the glutamate residues exposed to the lumen. The analysis also shows that a lower number of K ions bind at lower pH, modeled by a higher number of protons in the cation binding pocket, in agreement with the 'transport stoichiometry variation' hypothesis.
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http://dx.doi.org/10.1038/s41598-018-30885-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6109069PMC
August 2018

Importance of Solvents' Translational-Rotational Coupling for Translational Jump of a Small Hydrophobic Solute in Supercooled Water.

J Phys Chem B 2018 08 23;122(30):7569-7583. Epub 2018 Jul 23.

Department of Chemistry , Indian Institute of Technology Patna , Patna 801103 , Bihar , India.

Despite clear evidence of sudden translational jump occurrence of a solute in supercooled water, a detailed mechanism of this jump is still lacking. A previous work [ Indra , S. ; Daschakraborty , S. Chem. Phys. Lett. 2017 , 685 , 322 - 327 ] put forward a mechanism of this jump from an initial solvent cage to a final one. The proposed mechanism is astoundingly similar to that of the electron/proton transfer reaction in aqueous solution. The above study identified the spatial prearrangement (rearrangement before the jump occurrence) of cage forming water solvent molecules as the actual reaction coordinate. However, the study completely ignored the contribution of the orientational prearrangement of solvent water molecules. In this study, we have monitored both the spatial and the orientational prearrangements of water solvent molecules at subzero temperatures during the jump occurrence of the solute. We have found overwhelming contributions of both the spatial and orientational prearrangements of water, which symmetrize the hydration structure at the initial and final cage positions to facilitate the jump event. Through a systematic temperature dependence study (from T = 240 to 270 K), we have found clear evidence that a strong synchronization between translational and rotational prearrangements of the solvent water molecules is crucial for the solute's jump from one solvent cage to another in supercooled water (below T = 252 K). The above translation-rotation synchronization is probably due to the cooperative movement of solvent water molecules forming clusters in the supercooled region. Since these cooperative dynamics are the consequence of the spatiotemporal heterogeneity in the medium, we infer that the large-amplitude translational jump of the nonpolar solute probably stems from the spatiotemporal heterogeneity of supercooled water. At temperatures above the melting point, this cooperativity is partly lost since the translational and orientational prearrangements become somewhat independent of each other.
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http://dx.doi.org/10.1021/acs.jpcb.8b03177DOI Listing
August 2018

Interaction of N-terminal peptide analogues of the Na,K-ATPase with membranes.

Biochim Biophys Acta Biomembr 2018 Jun 6;1860(6):1282-1291. Epub 2018 Mar 6.

School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia; The University of Sydney Nano Institute, Sydney, NSW 2006, Australia. Electronic address:

The Na,K-ATPase, which is present in the plasma membrane of all animal cells, plays a crucial role in maintaining the Na and K electrochemical potential gradients across the membrane. Recent studies have suggested that the N-terminus of the protein's catalytic α-subunit is involved in an electrostatic interaction with the surrounding membrane, which controls the protein's conformational equilibrium. However, because the N-terminus could not yet be resolved in any X-ray crystal structures, little information about this interaction is so far available. In measurements utilising poly-l-lysine as a model of the protein's lysine-rich N-terminus and using lipid vesicles of defined composition, here we have identified the most likely origin of the interaction as one between positively charged lysine residues of the N-terminus and negatively charged headgroups of phospholipids (notably phosphatidylserine) in the surrounding membrane. Furthermore, to isolate which segments of the N-terminus could be involved in membrane binding, we chemically synthesized N-terminal fragments of various lengths. Based on a combination of results from RH421 UV/visible absorbance measurements and solid-state P and H NMR using these N-terminal fragments as well as MD simulations it appears that the membrane interaction arises from lysine residues prior to the conserved LKKE motif of the N-terminus. The MD simulations indicate that the strength of the interaction varies significantly between different enzyme conformations.
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http://dx.doi.org/10.1016/j.bbamem.2018.03.002DOI Listing
June 2018

Estimating the Lipophobic Contributions in Model Membranes.

J Phys Chem B 2017 03 22;121(9):2111-2120. Epub 2017 Feb 22.

Physical Chemistry Division, National Chemical Laboratory , Pune 411008, India.

The insertion and association of membrane proteins is critical in several cellular processes. These processes were thought to be protein-driven, but increasing evidence points toward an important role of the lipid bilayer. The lipid-mediated contribution has been shown to be important in the association of membrane peptides, but the corresponding "lipophobic" component has not been directly estimated. Here, we calculate the free energy of insertion for transmembrane peptides and estimate the lipophobic component from the cost of cavity formation. The free-energy calculations were performed using the coarse-grain Martini force field, which has been successful in predicting membrane protein interactions. As expected, the charged moieties have the least favorable free energy of insertion and the highest cost of cavity formation. A length dependence was observed in polyalanine peptides with the lipid-mediated component increasing nonlinearly with peptide length. Membrane fluidity was tested by varying the temperature, and opposing effects were observed for short and long peptides. The dependence of the lipid-mediated effects on peptide length and temperature was not uniform and gives valuable insight into the anisotropic nature of the membrane. The results are an important step in estimating membrane effects in protein insertion and association.
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http://dx.doi.org/10.1021/acs.jpcb.6b09863DOI Listing
March 2017

Mechanoluminescence Study of Europium Doped CaZrO3 Phosphor.

J Fluoresc 2016 Jul 16;26(4):1309-15. Epub 2016 May 16.

Department of Physics, Government Model Science College, Jabalpur, M. P., India.

Behaviour displayed by mechanoluminescence (ML) in CaZrO3:Eu(3+) doped phosphors with variable concentration of europium ions are described. When the ML is excited impulsively by the impact of a load on the phosphors the ML intensity increases with time, attains a maximum value and then it decreases. In the ML intensity versus time curve, the peak increases and shifts towards shorter time values with increasing impact velocities. Sample was synthesized by combustion synthesis method with variable concentration of Eu(3+) ions (0.1, 0.2, 0.5, 1, 1.5 mol%) and characterized by X-ray diffraction technique. The total ML intensity IT is defined as the area below the ML intensity versus time curve. Initially IT increases with impact velocity V0 of the load and then it attains a saturation value for higher values of impact velocities which follow the relation IT = IT (0) exp.(-Vc/V0) where IT (0) and Vc are constants. Total ML intensity increases linearly with the mass of the phosphors for higher impact velocities. The ML intensity Im, corresponding to the peak of ML intensity versus time curve increases linearly with the impact velocities. The time tm, is found to be linearly related to 1000/V0. The mechanoluminescence induced by impulsive excitation in europium doped CaZrO3 phosphors plays a significance role in the understanding of biological sensors and display device application.
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http://dx.doi.org/10.1007/s10895-016-1817-0DOI Listing
July 2016

PL Properties of Sr2CeO4 With Eu(3+) and Dy(3+) for Solid State Lighting Prepared by Precipitation Method.

J Fluoresc 2016 May 9;26(3):791-806. Epub 2016 Feb 9.

Department of Physics, R.T.M. Nagpur University, Nagpur, 440033, India.

Photoluminescence studies of pure and Dy(3+), Eu(3+) doped Sr2CeO4 compounds are presented by oxalate precipitation method for solid state lighting. The prepared samples also characterized by XRD, SEM (EDS) and FTIR spectroscopy. The pure Sr2CeO4 compound displays a broad band in its emission spectrum when excited with 280 nm wavelength, which peaks centered at 488 nm, which is due to the energy transfer between the molecular orbital of the ligand and charge transfer state of the Ce(4+) ions. Emission spectra of Sr2CeO4 with different concentration of Dy(3+) ions under near UV radiation excitation, shows that intensity of luminescence spectra is found to be affected by Dy(3+) ions, and it increases with adding some percentages of Dy(3+) ions. The maximum doping concentration for quenching is found to be Dy(3+) = 0.2 mol % to Sr(2+)ions. The observed broad spectrum from 400 to 560 nm is mainly due to CT transitions in Sr2CeO4 matrix and some fractional contribution of transitions between (4)F9/2 → (6)H15/2 of Dy(3+) ions. Secondly the effect of Eu(3+) doping at the Sr(2+) site in Sr2CeO4, have been studied. The results obtained by doping Eu(3+) concentrations (0.2 mol% to 1.5 mol%), the observed excitation and emission spectra reveal excellent energy transfer between Ce(4+) and Eu(3+). The phenomena of concentration quenching are explained on the basis of electron phonon coupling and multipolar interaction. This energy transfer generates white light with a color tuning from blue to red, the tuning being dependent on the Eu(3+) concentration. The results establish that the compound Sr2CeO4 with Eu(3+) = 1 mol% is an efficient "single host lattice" for the generation of white lights under near UV-LED and blue LED irradiation. The commission internationale de I'Eclairage (CIE) coordinates were calculated by Spectrophotometric method using the spectral energy distribution of prepared phosphors.
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http://dx.doi.org/10.1007/s10895-016-1765-8DOI Listing
May 2016

Study of formation of deep trapping mechanism by UV, beta and gamma irradiated Eu(3+) activated SrY2O4 and Y4Al2O9 phosphors.

Appl Radiat Isot 2016 Apr 19;110:16-27. Epub 2015 Dec 19.

Display Materials Laboratory, Applied Physics Department, Faculty of Technology and Engineering, The M. S. University of Baroda, Vadodara 390001 India.

This paper reports the thermoluminescence properties of Eu(3+) doped different host matrix phosphors (SrY2O4 and Y4Al2O9). The phosphor is prepared by high temperature solid state reaction method. The method is suitable for large scale production and fixed concentration of boric acid using as a flux. The prepared samples were characterized by X-ray diffraction technique and the crystallite size calculated by Scherer's formula. The prepared phosphor characterized by Scanning Electron Microscopic (SEM), Fourier Transform Infrared (FTIR), Energy Dispersive X-ray analysis (EDX), thermoluminescence (TL) and Transmission Electron Microscopic (TEM) techniques. The prepared phosphors for different concentration of Eu(3+) ions were examined by TL glow curve for UV, beta and gamma irradiation. The UV 254nm source used for UV irradiation, Sr(90) source was used for beta irradiation and Co(60) source used for gamma irradiation. SrY2O4:Eu(3+)and Y4Al2O9:Eu(3+) phosphors which shows both higher temperature peaks and lower temperature peaks for UV, beta and gamma irradiation. Here UV irradiated sample shows the formation of shallow trap (surface trapping) and the gamma irradiated sample shows the formation of deep trapping. The estimation of trap formation was evaluated by knowledge of trapping parameters. The trapping parameters such as activation energy, order of kinetics and frequency factor were calculated by peak shape method. Here most of the peak shows second order of kinetics. The effect of gamma, beta and UV exposure on TL studies was also examined and it shows linear response with dose which indicate that the samples may be useful for TL dosimetry. Formation of deep trapping mechanism by UV, beta and gamma irradiated Eu(3+) activated SrY2O4 and Y4Al2O9 phosphors is discussed in this paper.
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http://dx.doi.org/10.1016/j.apradiso.2015.12.047DOI Listing
April 2016

White Light Emission by Dy3+ Doped Phosphor Matrices: A Short Review.

J Fluoresc 2016 Jan;26(1):105-11

In this review we have studied number of research papers related to white light emission from Dy3+ doped different host matrices. It is observed that most of the Dy3+doped aluminates, silicates, borates etc., emitted blue, green and red colour with specific intensities so that CIE coordinates, appeared near to white light. Correlated Colour Temperature(CCT) values of these phosphors expressed that the white light emission produced, was adaptable to human eyes. Dy3+ ions act as activator in each case. Four peaks at approximately 480,575, 670, and 757 nm could be seen in most of the Dy3+ doped phosphors. Expected transition responsible for these peaks are 4F9/2 → 6H15/2 (Blue Colour), 4F9/2 → 6H13/2 (Green-Yellow Colour), 4F9/2 → 6H11/2 (Red Colour) and 4F9/2 → 6H9/2(Brownish Red Colour). Few of the discussed phosphors exhibited long phosphorescence, starting from several minutes to few hours. Mechanism responsible for long lasting white light emission was also discussed. Five different factors, to recognize the phosphors for its suitability as commercial white light phosphor have been discussed.
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http://dx.doi.org/10.1007/s10895-015-1689-8DOI Listing
January 2016

Luminescence studies and infrared emission of erbium-doped calcium zirconate phosphor.

Luminescence 2016 May 12;31(3):837-42. Epub 2015 Oct 12.

Department of Physics, Bhilai Institute of Technology, Raipur, India.

The near-infrared-to-visible upconversion luminescence behaviour of Er(3+)-doped CaZrO3 phosphor is discussed in this manuscript. The phosphor was prepared by a combustion synthesis technique that is suitable for less-time-taking techniques for nanophosphors. The starting materials used for sample preparation were Ca(NO3)2.4H2O, Zr(NO3)4 and Er(NO3)2, and urea was used as a fuel. The prepared sample was characterized by X-ray diffraction (XRD). The surface morphology of prepared phosphor was determined by field emission gun scanning electron microscopy (FEGSEM). The functional group analysis was determined by Fourier transform infrared (FTIR) spectroscopy. All prepared phosphors with variable Er(3+) concentrations (0.5-2.5 mol%) were studied by photoluminescence analysis. It was found that the excitation spectra of the prepared phosphor showed a sharp excitation peak centred at 980 nm. The emission spectra with variable Er(3+) concentrations showed strong peaks in the 555 nm and 567 nm range, with a dominant peak at 555 nm due to the ((2)H(11/2),(4)S(3/2)) transition and a weaker transition at 567 nm associated with 527 nm. Spectrophotometric determination of the peak was evaluated by the Commission Internationale de I'Eclairage (CIE) method These upconverted emissions were attributed to a two-photon process. The excitation wavelength dependence of the upconverted luminescence, together with its time evolution after infrared pulsed excitation, suggested that energy transfer upconversion processes were responsible for the upconversion luminescence. The upconversion mechanisms were studied in detail through laser power dependence. Excited state absorption and energy transfer processes were discussed as possible upconversion mechanisms. The cross-relaxation process in Er(3+) was also investigated.
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http://dx.doi.org/10.1002/bio.3039DOI Listing
May 2016

Fracto-mechanoluminescence induced by impulsive deformation of II-VI semiconductors.

Luminescence 2015 Sep 9;30(6):883-90. Epub 2015 Feb 9.

547, HIG-1, Sector-2, Pt. Deendayal Upadhyay Nagar, Raipur, Chattisgarh, 492010, India.

When II-VI semiconductors are fractured, initially the mechanoluminescence (ML) intensity increases with time, attains a maximum value Im at a time tm, at which the fracture is completed. After tm, the ML intensity decreases with time, Im increase linearly with the impact velocity v0 and IT initially increase linearly with v0 and then it attains a saturation value for a higher value of v0. For photoluminescence, the temperature dependence comes mainly from luminescence efficiency, ηo; however, for the ML excitation, there is an additional factor, rt dependent on temperature. During fracture, charged dislocations moving near the tip of moving cracks produce intense electric field, causes band bending. Consequently, tunneling of electrons from filled electron traps to the conduction band takes place, whereby the radiative electron-hole recombination give rise to the luminescence. In the proposed mechanism, expressions are derived for the rise, the time tm corresponding to the ML intensity versus time curve, the ML intensity Im corresponding to the peak of ML intensity versus time curve, the total fracto-mechanoluminescence (FML) intensity IT, and fast and slow decay of FML intensity of II-VI semiconductors. The FML plays a significant role in understanding the processes involved in biological detection, earthquake lights and mine failure.
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http://dx.doi.org/10.1002/bio.2837DOI Listing
September 2015