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Papers by rumi chand

Research paper thumbnail of Effect of Cu-Doping on the Photocatalytic Activity of TiO<sub>2</sub>/SiO<sub>2</sub> Beads

Research paper thumbnail of Highly water resistant surface coating by fluoride on long persistent Sr4Al14O25:Eu2+/Dy3+ phosphor

Applied Surface Science, 2010

A novel and efficient method of providing moisture resistance of inorganic particles such as diva... more A novel and efficient method of providing moisture resistance of inorganic particles such as divalent europium activated strontium aluminate phosphors (Sr 4 Al 14 O 25 :Eu 2+ /Dy 3+) was developed by firing the phosphor in the presence of appropriate amount of ammonium fluoride at a temperature of 600-700 8C. Scanning electron microscopy, X-ray diffraction, FT-IR, EDAX and Photoluminescence measurements were carried out to characterize the uncoated and coated samples. The pH measurements were carried out for the water resistivity measurements. The phosphor particles became coated with a moistureimpervious thin coating that did not suppress the luminescence of the phosphor and can withstand complete immersion in water for long periods of time, showing very high water resistivity.

Research paper thumbnail of Preparation of porous carbon from various agricultural wastes and its application for metal ions recovery

PREPARATION OF POROUS CARBON FROM VARIOUS AGRICULTURAL WASTES AND ITS APPLICATION FOR METAL IONS ... more PREPARATION OF POROUS CARBON FROM VARIOUS AGRICULTURAL WASTES AND ITS APPLICATION FOR METAL IONS RECOVERY Chairperson of the Supervisory Committee: Professor Takanori WATARI Department of Energy and Materials Science, Saga University Carbons were prepared from biomass like rice husk, barley and wheat straws by single-step carbonization at different carbonization temperature from 600-1000 C. The evolution of pore structure and surface chemistry during carbonization was investigated through surface area measurement. Potential of zero charge (PZC) measurement reveals that the surface of carbons was positively charged at acidic pH. Thus these biomass carbons were expected to adsorb metal ions which exist as anionic form in aqueous solution at acidic pH. The ability of using low-cost agro-waste carbon for Cr(VI) removal from the aquatic environment was studied in terms of solution pH, equilibrium Cr concentration and contact time. The optimum pH value was 2 for Cr(VI) adsorption and Cr(V...

Research paper thumbnail of Photocatalytic Wastewater Treatment Accelerated by Water Evaporation

Research paper thumbnail of ZnMoO4:Er3+,Yb3+ phosphor with controlled morphology and enhanced upconversion through alkali ions doping

Research paper thumbnail of A mechanism of the photocatalytic decomposition of 2,4-dinitrophenol on TiO2 immobilized on a glass surface

Chemical Engineering Journal

ABSTRACT A reaction mechanism of the photocatalytic decomposition of 2,4-dinitrophenol (DNP) on T... more ABSTRACT A reaction mechanism of the photocatalytic decomposition of 2,4-dinitrophenol (DNP) on TiO2 immobilized on a glass surface is investigated both theoretically and experimentally. The experimental results show that (1) the DNP concentration decreases linearly in the same manner; (2) the initial rate of decomposition increases with an increase in the initial DNP concentration, i.e., the reaction is not inhibited by DNP; and (3) product inhibition is present, but it is not as strong as that in the aqueous TiO2 suspension. To elucidate the mechanism of the photocatalytic reaction, a mathematical model is constructed by taking into consideration an electrostatic interaction between positively-charged TiO2 and negatively-charged DNP. The calculated results suggest that mixing a solution breaks down the DNP-aggregate layer formed in the neighborhood of TiO2 film and removes reactant inhibition by DNP. The results are also compared with our previous result for the DNP decomposition in an aqueous TiO2 suspension and the difference is identified.

Research paper thumbnail of Highly Efficient NIR to NIR Upconversion of ZnMoO4:Tm3+,Yb3+ Phosphor and its Application in Biological Imaging of Deep Tumors

J. Mater. Chem. B, 2016

In vivo imaging of deep tumor in nude-mice was successfully demonstrated using highly efficient Z... more In vivo imaging of deep tumor in nude-mice was successfully demonstrated using highly efficient ZnMoO4:Tm3+,Yb3+,K+ nano-phosphors and an 810 nm NIR laser.

Research paper thumbnail of Y2BaZnO5:Er3+ microcapsules with enhanced upconversion by vanadium ion codoping

RSC Adv., 2016

Er3+/V5+/Yb3+ doped Y2BaZnO5 microcapsules of 1–3 μm were prepared by HT route. Bright green to o... more Er3+/V5+/Yb3+ doped Y2BaZnO5 microcapsules of 1–3 μm were prepared by HT route. Bright green to orange UC was observed by dual 800 and 980 nm laser excitation. More than 3 fold intensification of Er UC was achieved by 3 mol% V5+ substitution.

Research paper thumbnail of CaMoO4:RE3+,Yb3+,M+ phosphor with controlled morphology and color tunable upconversion

Research paper thumbnail of Recovery and Separation of Precious Metals Using Waste Paper

Chemistry Letters, 2007

An adsorption gel was prepared from waste paper by immobilizing iminodiacetic acid so as to inves... more An adsorption gel was prepared from waste paper by immobilizing iminodiacetic acid so as to investigate its adsorption behavior for various metal ions from chloride media. The gel was found to be selective for Au III and Pd II over Pt IV and other base metal ions including ...

Research paper thumbnail of A Novel Orange-Red Emitting ZnB 4 O 7 :Eu 3+ Phosphor with Urchin-Like Nanostructure

Advances in Condensed Matter Physics, 2015

A novel phosphor, ZnB4O7:Eu3+, with urchin-like structure consisting of radially arranged high de... more A novel phosphor, ZnB4O7:Eu3+, with urchin-like structure consisting of radially arranged high density nanorods was successfully synthesized by hydrothermal process at 150°C for 24 h. The nanorods were measured from 200 to 400 nm in diameter and severalµm in length. The urchins were fewµm to 40 µm in diameter. The ZnB4O7:Eu3+phosphors were efficiently excited by ultraviolet (UV ~ 254 nm) to visible light of ~ 220 to 450 nm and exhibited intense orange-red emission consisting of main peaks at 590, 615, and 695 nm due to the charge transfer in the host andf→ftransitions (5D0to7F1,2,4) of the Eu3+ions. Effect of the Eu3+ions concentration on the photoluminescence (PL) emission intensity was investigated and it was found that 5 at% Eu3+is the optimum concentration. Meanwhile, the concentration quenching mechanism was discussed. The key parameters, such as temperature dependent PL and CIE values of ZnB4O7:Eu3+phosphors, were studied. The ZnB4O7:Eu3+phosphor exhibited good thermal stabili...

Research paper thumbnail of 2013 Giant Improvement on the Afterglow of Sr4Al14O25;Eu2+,Dy3+ Phosphor by Systematic Investigation on Various Parameters

Highly intense, long persistent Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ blue-green phosphor with different ... more Highly intense, long persistent Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ blue-green phosphor with different B 3+ , Eu 2+ , Dy 3+ , and Ag + contents was prepared by solid-phase reaction at various temperatures in reductive atmosphere of 10% H 2 in N 2. The effects of synthesis parameters like calcination temperature and time, calcination environment, effect of stoichiometry of the host composition, and additives like addition of boron and rare earth ions (Eu, Dy) were studied in detail. Results revealed that the phosphor containing ∼40 mol% H 3 BO 3 showed dense and pure Sr 4 Al 14 O 25 phase with higher emission intensity, but in the samples containing less than 20 mol% H 3 BO 3 mixed phases consisting of Al 2 O 3 , SrAl 12 O 19 and SrAl 2 O 4 were observed, while in higher H 3 BO 3 content, SrAl 2 B 2 O 7 phases predominated. When the stoichiometry of Al/Sr was 3.7, the best phosphorescence and afterglow were noted. The phosphor containing 4 at.% of Eu and 8 at.% of Dy, and 3 at.% Ag exhibited the maximum initial intensity of 5170 mcd⋅m −2 and the longest persistency of greater than 30 hours over the value of 5 mcd⋅m −2 , higher than the commercial products and applicable for various display applications involving indoor as well as outdoor uses.

Research paper thumbnail of Bright Orange upconversion on ZnO-TiO2;Er,Yb phosphor Optical Materials 36 (2014) 591–595

ZnO-TiO 2 composite system containing Er 3+ and Yb 3+ were prepared by solid state reaction metho... more ZnO-TiO 2 composite system containing Er 3+ and Yb 3+ were prepared by solid state reaction method and its upconversion (UC) luminescence excited by 980 nm laser was studied for the first time. The effects of firing temperature, ZnO/TiO 2 composition and Er 3+ , Yb 3+ concentrations on the UC emission behavior were examined. The ZnO-TiO 2 composite product sintered at 1200°C contained Zn 2 TiO 4 , TiO 2 and RE 2 Ti 2 O 7 (RE = Er 3+ and Yb 3+) phases and exhibited strong green and red emissions arising due to the 2 H 11/2 , 4 S 3/2 ? 4 I 15/2 and 4 F 9/2 ? 4 I 15/2 transitions for Er 3+ ion, respectively. Bright orange color by the mixing of green and red colors was observed in the 1ZnO-1TiO 2 product doped with 2 at.% Er 3+ and 6 at.% Yb 3+. The ZnO-TiO 2 :Er 3+ , Yb 3+ phosphor was compared to the brightest available phosphor, Y 2 O 3 :Er 3+ , Yb 3+ and found to be 3-fold brighter than it. It suggests that ZnO-TiO 2 :Er 3+ , Yb 3+ is a potential material for the orange upconversion phosphor.

Research paper thumbnail of Design of Long Persistent White Phosphorescence in a Composite Phosphor Via Energy Transfer Mechanism

International Journal of Materials Science and Applications, 2015

A high quality composite phosphor powder of warm to cool white emission and long afterglow phosph... more A high quality composite phosphor powder of warm to cool white emission and long afterglow phosphorescence was reported by the process of energy transfer in a composite phosphor. The composite phosphor particles include at least two types of phosphor particles viz. a blue white persistent component and yellow fluorescent component. The blue white extremely long persistent component transfers its afterglow to the yellow fluorescent component in the composite phosphor followed by the color mixing process to generate the white afterglow. The composite phosphor is designed in such a way that the excitation spectrum of the fluorescent component was overlapped as much with the afterglow emission of the persistent component. The composite phosphor emission spectrum can be well tuned from warm to cool white depending on the proportions of the composite phosphors and energy transfer extent. Phosphor includes powders, ceramics and resin composites.

Research paper thumbnail of Adsorption Behavior of Barley Straw Carbon for Chromium (VI) Ion

Materials Science Forum, 2008

Porous carbon having surface area of 792 m2g-1 was prepared from barley straw by carbonization at... more Porous carbon having surface area of 792 m2g-1 was prepared from barley straw by carbonization at 800 oC at a heating rate of 5 oCmin-1 to test the chromium (VI) adsorption from aqueous solution. The effects of pH, contact time and equilibrium Cr (VI) concentration on the adsorption were studied in detail. The optimum pH for Cr (VI) removal was found to be 2. The adsorption of Cr (VI) was very rapid and equilibrium was reached within 1 h. It was interpreted in terms of adsorption-coupled reduction mechanism. Accompanied by the decrease of Cr (VI) ion, Cr (III) ion was slightly released in the solution. Maximum loading capacity of total chromium was found to be 2.35 molkg-1 at pH 2.

Research paper thumbnail of Rare Earth Free Zn 3 V 2 O 8 Phosphor with Controlled Microstructure and Its Photocatalytic Activity

International Journal of Photoenergy, 2013

Microsphere of rare earth free phosphor,Zn3V2O8, with broadband yellowish white emission was synt... more Microsphere of rare earth free phosphor,Zn3V2O8, with broadband yellowish white emission was synthesized by combustion route and compared with the hydrothermal, sol-gel, and solid state reaction methods. The phosphor samples were characterized by X-ray diffraction and scanning electron microscopy. UV-visible absorption and photoluminescence (PL) emission and excitation spectra were investigated for these phosphors.Zn3V2O8phosphor containing 10 mol% of H3BO3flux exhibited enhanced PL emission showing broadband from 450 nm to 750 nm. Effect of stoichiometry of Zn and V on the host lattice and its effect on the PL emission spectra were studied. Series of Mg3V2O8,Ca3V2O8, and Sr3V2O8phosphors were also synthesized and compared to theZn3V2O8phosphor in terms of PL emission and internal quantum yield, and it was found thatZn3V2O8is the most efficient phosphor among the other phosphors studied with quantum yield of 60%. The visible light irradiated photocatalytic activity of these phosphor...

Research paper thumbnail of Highly efficient NIR–NIR upconversion in potassium substituted CaMoO 4 :Tm 3+ , Yb 3+ phosphor for potential biomedical applications

RSC Adv., 2015

Highly efficient NIR to NIR upconversion in CaMoO4:Tm3+, Yb3+ nanocrystals pumped by less than 1 ... more Highly efficient NIR to NIR upconversion in CaMoO4:Tm3+, Yb3+ nanocrystals pumped by less than 1 mW laser was achieved for biomedical applications.

Research paper thumbnail of Bright orange upconversion in a ZnO–TiO2 composite containing Er3+ and Yb3+

Optical Materials, 2014

ABSTRACT ZnO–TiO2 composite system containing Er3+ and Yb3+ were prepared by solid state reaction... more ABSTRACT ZnO–TiO2 composite system containing Er3+ and Yb3+ were prepared by solid state reaction method and its upconversion (UC) luminescence excited by 980 nm laser was studied for the first time. The effects of firing temperature, ZnO/TiO2 composition and Er3+, Yb3+ concentrations on the UC emission behavior were examined. The ZnO–TiO2 composite product sintered at 1200 °C contained Zn2TiO4, TiO2 and RE2Ti2O7 (RE = Er3+ and Yb3+) phases and exhibited strong green and red emissions arising due to the 2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions for Er3+ ion, respectively. Bright orange color by the mixing of green and red colors was observed in the 1ZnO–1TiO2 product doped with 2 at.% Er3+ and 6 at.% Yb3+. The ZnO–TiO2:Er3+, Yb3+ phosphor was compared to the brightest available phosphor, Y2O3:Er3+, Yb3+ and found to be 3-fold brighter than it. It suggests that ZnO–TiO2:Er3+, Yb3+ is a potential material for the orange upconversion phosphor.

Research paper thumbnail of Giant Improvement on the Afterglow of Sr4Al14O25:Eu2+,Dy3+ Phosphor by Systematic Investigation on Various Parameters

Journal of Materials, 2013

Highly intense, long persistent Sr4Al14O25:Eu2+,Dy3+blue-green phosphor with different B3+, Eu2+,... more Highly intense, long persistent Sr4Al14O25:Eu2+,Dy3+blue-green phosphor with different B3+, Eu2+, Dy3+, and Ag+contents was prepared by solid-phase reaction at various temperatures in reductive atmosphere of 10% H2in N2. The effects of synthesis parameters like calcination temperature and time, calcination environment, effect of stoichiometry of the host composition, and additives like addition of boron and rare earth ions (Eu, Dy) were studied in detail. Results revealed that the phosphor containing ~40 mol% H3BO3showed dense and pure Sr4Al14O25phase with higher emission intensity, but in the samples containing less than 20 mol% H3BO3mixed phases consisting of Al2O3, SrAl12O19and SrAl2O4were observed, while in higher H3BO3content, SrAl2B2O7phases predominated. When the stoichiometry of Al/Sr was 3.7, the best phosphorescence and afterglow were noted. The phosphor containing 4 at.% of Eu and 8 at.% of Dy, and 3 at.% Ag exhibited the maximum initial intensity of 5170 mcd·m−2and the l...

Research paper thumbnail of Evaluation of wheat straw and barley straw carbon for Cr(VI) adsorption

Separation and Purification Technology, 2009

The present study deals with the adsorption of Cr(VI) on carbonized wheat straw (CWS) and barley ... more The present study deals with the adsorption of Cr(VI) on carbonized wheat straw (CWS) and barley straw (CBS). Carbon materials, prepared at different carbonization temperatures, were investigated for the adsorptive removal of Cr(VI). These carbonized materials prepared from agro-waste were found to have a high affinity for chromium as represented by very high adsorption capacities of 1.67 and 1.68 mol/kg for wheat and barley straws, respectively, carbonized at 800 • C at pH 2. Equilibrium was reached within 1 h of contact time which suggests high efficiency of the carbonized materials for Cr(VI) removal.

Research paper thumbnail of Effect of Cu-Doping on the Photocatalytic Activity of TiO<sub>2</sub>/SiO<sub>2</sub> Beads

Research paper thumbnail of Highly water resistant surface coating by fluoride on long persistent Sr4Al14O25:Eu2+/Dy3+ phosphor

Applied Surface Science, 2010

A novel and efficient method of providing moisture resistance of inorganic particles such as diva... more A novel and efficient method of providing moisture resistance of inorganic particles such as divalent europium activated strontium aluminate phosphors (Sr 4 Al 14 O 25 :Eu 2+ /Dy 3+) was developed by firing the phosphor in the presence of appropriate amount of ammonium fluoride at a temperature of 600-700 8C. Scanning electron microscopy, X-ray diffraction, FT-IR, EDAX and Photoluminescence measurements were carried out to characterize the uncoated and coated samples. The pH measurements were carried out for the water resistivity measurements. The phosphor particles became coated with a moistureimpervious thin coating that did not suppress the luminescence of the phosphor and can withstand complete immersion in water for long periods of time, showing very high water resistivity.

Research paper thumbnail of Preparation of porous carbon from various agricultural wastes and its application for metal ions recovery

PREPARATION OF POROUS CARBON FROM VARIOUS AGRICULTURAL WASTES AND ITS APPLICATION FOR METAL IONS ... more PREPARATION OF POROUS CARBON FROM VARIOUS AGRICULTURAL WASTES AND ITS APPLICATION FOR METAL IONS RECOVERY Chairperson of the Supervisory Committee: Professor Takanori WATARI Department of Energy and Materials Science, Saga University Carbons were prepared from biomass like rice husk, barley and wheat straws by single-step carbonization at different carbonization temperature from 600-1000 C. The evolution of pore structure and surface chemistry during carbonization was investigated through surface area measurement. Potential of zero charge (PZC) measurement reveals that the surface of carbons was positively charged at acidic pH. Thus these biomass carbons were expected to adsorb metal ions which exist as anionic form in aqueous solution at acidic pH. The ability of using low-cost agro-waste carbon for Cr(VI) removal from the aquatic environment was studied in terms of solution pH, equilibrium Cr concentration and contact time. The optimum pH value was 2 for Cr(VI) adsorption and Cr(V...

Research paper thumbnail of Photocatalytic Wastewater Treatment Accelerated by Water Evaporation

Research paper thumbnail of ZnMoO4:Er3+,Yb3+ phosphor with controlled morphology and enhanced upconversion through alkali ions doping

Research paper thumbnail of A mechanism of the photocatalytic decomposition of 2,4-dinitrophenol on TiO2 immobilized on a glass surface

Chemical Engineering Journal

ABSTRACT A reaction mechanism of the photocatalytic decomposition of 2,4-dinitrophenol (DNP) on T... more ABSTRACT A reaction mechanism of the photocatalytic decomposition of 2,4-dinitrophenol (DNP) on TiO2 immobilized on a glass surface is investigated both theoretically and experimentally. The experimental results show that (1) the DNP concentration decreases linearly in the same manner; (2) the initial rate of decomposition increases with an increase in the initial DNP concentration, i.e., the reaction is not inhibited by DNP; and (3) product inhibition is present, but it is not as strong as that in the aqueous TiO2 suspension. To elucidate the mechanism of the photocatalytic reaction, a mathematical model is constructed by taking into consideration an electrostatic interaction between positively-charged TiO2 and negatively-charged DNP. The calculated results suggest that mixing a solution breaks down the DNP-aggregate layer formed in the neighborhood of TiO2 film and removes reactant inhibition by DNP. The results are also compared with our previous result for the DNP decomposition in an aqueous TiO2 suspension and the difference is identified.

Research paper thumbnail of Highly Efficient NIR to NIR Upconversion of ZnMoO4:Tm3+,Yb3+ Phosphor and its Application in Biological Imaging of Deep Tumors

J. Mater. Chem. B, 2016

In vivo imaging of deep tumor in nude-mice was successfully demonstrated using highly efficient Z... more In vivo imaging of deep tumor in nude-mice was successfully demonstrated using highly efficient ZnMoO4:Tm3+,Yb3+,K+ nano-phosphors and an 810 nm NIR laser.

Research paper thumbnail of Y2BaZnO5:Er3+ microcapsules with enhanced upconversion by vanadium ion codoping

RSC Adv., 2016

Er3+/V5+/Yb3+ doped Y2BaZnO5 microcapsules of 1–3 μm were prepared by HT route. Bright green to o... more Er3+/V5+/Yb3+ doped Y2BaZnO5 microcapsules of 1–3 μm were prepared by HT route. Bright green to orange UC was observed by dual 800 and 980 nm laser excitation. More than 3 fold intensification of Er UC was achieved by 3 mol% V5+ substitution.

Research paper thumbnail of CaMoO4:RE3+,Yb3+,M+ phosphor with controlled morphology and color tunable upconversion

Research paper thumbnail of Recovery and Separation of Precious Metals Using Waste Paper

Chemistry Letters, 2007

An adsorption gel was prepared from waste paper by immobilizing iminodiacetic acid so as to inves... more An adsorption gel was prepared from waste paper by immobilizing iminodiacetic acid so as to investigate its adsorption behavior for various metal ions from chloride media. The gel was found to be selective for Au III and Pd II over Pt IV and other base metal ions including ...

Research paper thumbnail of A Novel Orange-Red Emitting ZnB 4 O 7 :Eu 3+ Phosphor with Urchin-Like Nanostructure

Advances in Condensed Matter Physics, 2015

A novel phosphor, ZnB4O7:Eu3+, with urchin-like structure consisting of radially arranged high de... more A novel phosphor, ZnB4O7:Eu3+, with urchin-like structure consisting of radially arranged high density nanorods was successfully synthesized by hydrothermal process at 150°C for 24 h. The nanorods were measured from 200 to 400 nm in diameter and severalµm in length. The urchins were fewµm to 40 µm in diameter. The ZnB4O7:Eu3+phosphors were efficiently excited by ultraviolet (UV ~ 254 nm) to visible light of ~ 220 to 450 nm and exhibited intense orange-red emission consisting of main peaks at 590, 615, and 695 nm due to the charge transfer in the host andf→ftransitions (5D0to7F1,2,4) of the Eu3+ions. Effect of the Eu3+ions concentration on the photoluminescence (PL) emission intensity was investigated and it was found that 5 at% Eu3+is the optimum concentration. Meanwhile, the concentration quenching mechanism was discussed. The key parameters, such as temperature dependent PL and CIE values of ZnB4O7:Eu3+phosphors, were studied. The ZnB4O7:Eu3+phosphor exhibited good thermal stabili...

Research paper thumbnail of 2013 Giant Improvement on the Afterglow of Sr4Al14O25;Eu2+,Dy3+ Phosphor by Systematic Investigation on Various Parameters

Highly intense, long persistent Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ blue-green phosphor with different ... more Highly intense, long persistent Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ blue-green phosphor with different B 3+ , Eu 2+ , Dy 3+ , and Ag + contents was prepared by solid-phase reaction at various temperatures in reductive atmosphere of 10% H 2 in N 2. The effects of synthesis parameters like calcination temperature and time, calcination environment, effect of stoichiometry of the host composition, and additives like addition of boron and rare earth ions (Eu, Dy) were studied in detail. Results revealed that the phosphor containing ∼40 mol% H 3 BO 3 showed dense and pure Sr 4 Al 14 O 25 phase with higher emission intensity, but in the samples containing less than 20 mol% H 3 BO 3 mixed phases consisting of Al 2 O 3 , SrAl 12 O 19 and SrAl 2 O 4 were observed, while in higher H 3 BO 3 content, SrAl 2 B 2 O 7 phases predominated. When the stoichiometry of Al/Sr was 3.7, the best phosphorescence and afterglow were noted. The phosphor containing 4 at.% of Eu and 8 at.% of Dy, and 3 at.% Ag exhibited the maximum initial intensity of 5170 mcd⋅m −2 and the longest persistency of greater than 30 hours over the value of 5 mcd⋅m −2 , higher than the commercial products and applicable for various display applications involving indoor as well as outdoor uses.

Research paper thumbnail of Bright Orange upconversion on ZnO-TiO2;Er,Yb phosphor Optical Materials 36 (2014) 591–595

ZnO-TiO 2 composite system containing Er 3+ and Yb 3+ were prepared by solid state reaction metho... more ZnO-TiO 2 composite system containing Er 3+ and Yb 3+ were prepared by solid state reaction method and its upconversion (UC) luminescence excited by 980 nm laser was studied for the first time. The effects of firing temperature, ZnO/TiO 2 composition and Er 3+ , Yb 3+ concentrations on the UC emission behavior were examined. The ZnO-TiO 2 composite product sintered at 1200°C contained Zn 2 TiO 4 , TiO 2 and RE 2 Ti 2 O 7 (RE = Er 3+ and Yb 3+) phases and exhibited strong green and red emissions arising due to the 2 H 11/2 , 4 S 3/2 ? 4 I 15/2 and 4 F 9/2 ? 4 I 15/2 transitions for Er 3+ ion, respectively. Bright orange color by the mixing of green and red colors was observed in the 1ZnO-1TiO 2 product doped with 2 at.% Er 3+ and 6 at.% Yb 3+. The ZnO-TiO 2 :Er 3+ , Yb 3+ phosphor was compared to the brightest available phosphor, Y 2 O 3 :Er 3+ , Yb 3+ and found to be 3-fold brighter than it. It suggests that ZnO-TiO 2 :Er 3+ , Yb 3+ is a potential material for the orange upconversion phosphor.

Research paper thumbnail of Design of Long Persistent White Phosphorescence in a Composite Phosphor Via Energy Transfer Mechanism

International Journal of Materials Science and Applications, 2015

A high quality composite phosphor powder of warm to cool white emission and long afterglow phosph... more A high quality composite phosphor powder of warm to cool white emission and long afterglow phosphorescence was reported by the process of energy transfer in a composite phosphor. The composite phosphor particles include at least two types of phosphor particles viz. a blue white persistent component and yellow fluorescent component. The blue white extremely long persistent component transfers its afterglow to the yellow fluorescent component in the composite phosphor followed by the color mixing process to generate the white afterglow. The composite phosphor is designed in such a way that the excitation spectrum of the fluorescent component was overlapped as much with the afterglow emission of the persistent component. The composite phosphor emission spectrum can be well tuned from warm to cool white depending on the proportions of the composite phosphors and energy transfer extent. Phosphor includes powders, ceramics and resin composites.

Research paper thumbnail of Adsorption Behavior of Barley Straw Carbon for Chromium (VI) Ion

Materials Science Forum, 2008

Porous carbon having surface area of 792 m2g-1 was prepared from barley straw by carbonization at... more Porous carbon having surface area of 792 m2g-1 was prepared from barley straw by carbonization at 800 oC at a heating rate of 5 oCmin-1 to test the chromium (VI) adsorption from aqueous solution. The effects of pH, contact time and equilibrium Cr (VI) concentration on the adsorption were studied in detail. The optimum pH for Cr (VI) removal was found to be 2. The adsorption of Cr (VI) was very rapid and equilibrium was reached within 1 h. It was interpreted in terms of adsorption-coupled reduction mechanism. Accompanied by the decrease of Cr (VI) ion, Cr (III) ion was slightly released in the solution. Maximum loading capacity of total chromium was found to be 2.35 molkg-1 at pH 2.

Research paper thumbnail of Rare Earth Free Zn 3 V 2 O 8 Phosphor with Controlled Microstructure and Its Photocatalytic Activity

International Journal of Photoenergy, 2013

Microsphere of rare earth free phosphor,Zn3V2O8, with broadband yellowish white emission was synt... more Microsphere of rare earth free phosphor,Zn3V2O8, with broadband yellowish white emission was synthesized by combustion route and compared with the hydrothermal, sol-gel, and solid state reaction methods. The phosphor samples were characterized by X-ray diffraction and scanning electron microscopy. UV-visible absorption and photoluminescence (PL) emission and excitation spectra were investigated for these phosphors.Zn3V2O8phosphor containing 10 mol% of H3BO3flux exhibited enhanced PL emission showing broadband from 450 nm to 750 nm. Effect of stoichiometry of Zn and V on the host lattice and its effect on the PL emission spectra were studied. Series of Mg3V2O8,Ca3V2O8, and Sr3V2O8phosphors were also synthesized and compared to theZn3V2O8phosphor in terms of PL emission and internal quantum yield, and it was found thatZn3V2O8is the most efficient phosphor among the other phosphors studied with quantum yield of 60%. The visible light irradiated photocatalytic activity of these phosphor...

Research paper thumbnail of Highly efficient NIR–NIR upconversion in potassium substituted CaMoO 4 :Tm 3+ , Yb 3+ phosphor for potential biomedical applications

RSC Adv., 2015

Highly efficient NIR to NIR upconversion in CaMoO4:Tm3+, Yb3+ nanocrystals pumped by less than 1 ... more Highly efficient NIR to NIR upconversion in CaMoO4:Tm3+, Yb3+ nanocrystals pumped by less than 1 mW laser was achieved for biomedical applications.

Research paper thumbnail of Bright orange upconversion in a ZnO–TiO2 composite containing Er3+ and Yb3+

Optical Materials, 2014

ABSTRACT ZnO–TiO2 composite system containing Er3+ and Yb3+ were prepared by solid state reaction... more ABSTRACT ZnO–TiO2 composite system containing Er3+ and Yb3+ were prepared by solid state reaction method and its upconversion (UC) luminescence excited by 980 nm laser was studied for the first time. The effects of firing temperature, ZnO/TiO2 composition and Er3+, Yb3+ concentrations on the UC emission behavior were examined. The ZnO–TiO2 composite product sintered at 1200 °C contained Zn2TiO4, TiO2 and RE2Ti2O7 (RE = Er3+ and Yb3+) phases and exhibited strong green and red emissions arising due to the 2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions for Er3+ ion, respectively. Bright orange color by the mixing of green and red colors was observed in the 1ZnO–1TiO2 product doped with 2 at.% Er3+ and 6 at.% Yb3+. The ZnO–TiO2:Er3+, Yb3+ phosphor was compared to the brightest available phosphor, Y2O3:Er3+, Yb3+ and found to be 3-fold brighter than it. It suggests that ZnO–TiO2:Er3+, Yb3+ is a potential material for the orange upconversion phosphor.

Research paper thumbnail of Giant Improvement on the Afterglow of Sr4Al14O25:Eu2+,Dy3+ Phosphor by Systematic Investigation on Various Parameters

Journal of Materials, 2013

Highly intense, long persistent Sr4Al14O25:Eu2+,Dy3+blue-green phosphor with different B3+, Eu2+,... more Highly intense, long persistent Sr4Al14O25:Eu2+,Dy3+blue-green phosphor with different B3+, Eu2+, Dy3+, and Ag+contents was prepared by solid-phase reaction at various temperatures in reductive atmosphere of 10% H2in N2. The effects of synthesis parameters like calcination temperature and time, calcination environment, effect of stoichiometry of the host composition, and additives like addition of boron and rare earth ions (Eu, Dy) were studied in detail. Results revealed that the phosphor containing ~40 mol% H3BO3showed dense and pure Sr4Al14O25phase with higher emission intensity, but in the samples containing less than 20 mol% H3BO3mixed phases consisting of Al2O3, SrAl12O19and SrAl2O4were observed, while in higher H3BO3content, SrAl2B2O7phases predominated. When the stoichiometry of Al/Sr was 3.7, the best phosphorescence and afterglow were noted. The phosphor containing 4 at.% of Eu and 8 at.% of Dy, and 3 at.% Ag exhibited the maximum initial intensity of 5170 mcd·m−2and the l...

Research paper thumbnail of Evaluation of wheat straw and barley straw carbon for Cr(VI) adsorption

Separation and Purification Technology, 2009

The present study deals with the adsorption of Cr(VI) on carbonized wheat straw (CWS) and barley ... more The present study deals with the adsorption of Cr(VI) on carbonized wheat straw (CWS) and barley straw (CBS). Carbon materials, prepared at different carbonization temperatures, were investigated for the adsorptive removal of Cr(VI). These carbonized materials prepared from agro-waste were found to have a high affinity for chromium as represented by very high adsorption capacities of 1.67 and 1.68 mol/kg for wheat and barley straws, respectively, carbonized at 800 • C at pH 2. Equilibrium was reached within 1 h of contact time which suggests high efficiency of the carbonized materials for Cr(VI) removal.