Radenka M. Krsmanović

Adsorption of sulfur onto a surface of silver nanoparticles stabilized with sago starch biopolymer.

Adsorption of sulfide ions onto a surface of starch capped silver nanoparticles upon addition of thioacetamide was investigated. UV-vis absorption spectroscopy revealed that the adsorption of the sulfide ion on the surface of the silver nanoparticles induced damping as well as blue shift of the silver surface plasmon resonance band. Further increase in thioacetamide concentration led to shift of the resonance band toward higher wavelengths indicating the formation of the continuous Ag2S layer on the silver surface. Thus fabricated nanoparticles were investigated using electron microscopy techniques (TEM, HRTEM, and HAADF-STEM) and X-ray photoelectron spectroscopy (XPS), which confirmed their core-shell structure.

Inhibition of Microbial Growth by Silver–Starch Nanocomposite Thin Films

A sago starch biopolymer with embedded silver nanoparticles has been studied as a material for the prevention of microbial growth. Approximately 8 nm in size, silver nanoparticles have been synthesized by reduction of the silver salt in aqueous solution in the presence of sago starch using sodium borohydride as a reducing agent. The obtained solutions were cast on glass plates to obtain thin supported silver–starch nanocomposite films. The morphology of the nanocomposites was investigated by scanning and transmission electron microscopy. UV-Vis absorption spectroscopy showed that during the film formation a part of the silver nanoparticles has been trapped in the water present in the sample, which enabled their partial oxidation into active Ag+ species. The oxidation of the silver nanoparticles was confirmed by X-ray photoelectron spectroscopy. The antimicrobial activity tests have shown that the nanocomposite material can be successfully employed to prevent the viability and growth of the common pathogens Staphylococcus aureus, Escherichia coli and Candida albicans.

Characterization of Nanoporous Lanthanide-Doped Gadolinium Gallium Garnet Powders Obtained by Propellant Synthesis

In the present work we study the nanocrystalline powders of lanthanide-doped Gd3Ga5O12 (GGG, gadolinium gallium garnet) prepared using propellant synthesis. A series of GGG samples containing a number of different trivalent lanthanide ions (Tm, Er, Ho, Eu, Sm, Nd, and Pr) in different quantities (1%, 5%, 10%) were produced. Samples were characterized by X-ray diffraction (pre- and post calcination) for phase identification and line-broadening analysis, and by electron microscopy (SEM and TEM) for morphological and nanostructural investigation. Thermal behavior of the powder was investigated by thermal gravimetric analysis (TGA) and differential thermal analysis (DTA). The samples have a polycrystalline porous structure. Elemental microanalysis made by energy dispersive X-ray spectroscopy (EDX) detector attached to TEM and XRD unit-cell determinations confirmed that the lanthanides ions entered the structure of GGG. Crystallites have a high degree of disorder.

Structural Investigation and Anti-Stokes Emission of Scandium Oxide Nanocrystals Activated with Trivalent Erbium

The structural and emission (Stokes and anti-Stokes) properties of Sc 2 O 3 :Er 3 + nanocrystals doped with 0.1, 1, and 10 mol % Er 3 + were investigated. The nanocrystalline powders were characterized using X-ray scattering as well as transmission and scanning electron microscopy. The samples showed a very porous, open microstructure with the particles having a narrow distribution of sizes (10-60 nm). Furthermore, the mechanisms responsible for the anti-Stokes emission (λ e x c = 980 nm) were elucidated. We observed that the processes responsible for populating the green ( 2 H 1 1 / 2 , 4 S 3 / 2 ) and red ( 4 F 9 / 2 ) emitting states were dependent upon the concentration of the dopant ion. In 0.1 mol % nanocrystalline Sc 2 O 3 :E 3 + , upconversion was determined to occur via excited state absorption while in the 10 mol % sample, energy transfer upconversion was the dominant mechanism. An enhancement of the red anti-Stokes emission from the 4 F 9 / 2 → 4 I 1 5 / 2 transition was observed in Sc 2 O 3 :Er 3 + nanocrystals as a function of Er 3 + concentration. This was the result of two independent processes responsible for directly populating the 4 F 9 / 2 state and bypassing the green emitting levels ( 2 H 1 1 / 2 and 4 S 3 / 2 ). Furthermore, the red enhancement was found to be more pronounced compared to identically doped Y 2 O 3 :Er 3 + nanocrystals. An explanation for this phenomenon is presented and discussed.

Thermographic properties of Sm3+-doped GdVO4 phosphor

Rare-earth orthovanadates are important hosts for the luminescence of rare earth activators with considerable practical applications in the artificial production of light. In this paper we investigated the possibility for GdVO4:Sm3+ usage in phosphor thermometry by observing the temperature changes of trivalent samarium transitions from 4F3/2 and 4G5/2 energy levels to the ground state. A set of three samples of Sm3+-doped GdVO4 (0.5, 1 and 2 mol.% Sm3+ with respect to Gd3+ ions) was produced via solid state synthesis. The sample crystalline structure is confirmed from x-ray diffraction (XRD) measurements. Photoluminescence measurements were recorded in the temperature range 293–823 K and the fluorescence intensity ratio of the paired emissions bands was studied as a function of temperature. All three GdVO4:Sm3+ samples proved to have good potential for the development of thermographic phosphors, whereas the maximum sensitivity of approximately 4.5×10-4 K−1 was found for the sample with 2 mol.% Sm3+ in the temperature region around 750 K.

Characterization of nanoporous Lanthanide-doped YAG powders obtained by propellant synthesis

In the present work, we explored the possibility of obtaining nanocrystalline powders of lanthanide-doped Y3Al5O12 (YAG, yttrium aluminum garnet) using solution propellant synthesis, a novel technique that has been proven to be capable of producing nanopowders of numerous oxides at relatively low temperatures and in a rapid way. A series of YAG samples containing a number of different trivalent lanthanide ions (Eu, Er, Ho, Tm) was produced. Samples were characterized by X-ray diffraction for phase identification and line broadening analysis, and by electron microscopy (SEM and HRTEM) for morphological and nanostructural investigation. The samples have a polycrystalline porous structure made up of particles in the nanometer range. Crystallites have a high degree of disorder; the ones doped with Eu 3+ are characterized by an intense and well-resolved luminescence spectrum in the visible region.

PMMA/Zn 2 SiO 4 :Eu 3+ (Mn 2+ ) Composites: Preparation, Optical, and Thermal Properties

Luminescent composites of poly(methylmethacrylate) (PMMA) and nanophosphors (Zn2SiO4:Mn2+, Zn2SiO4:Eu3+) were prepared by dispersion casting method. It was found that nanoparticles embedded in PMMA matrix preserve their typical phosphorescence emission. The influence of Zn2SiO4 nanofillers on thermal properties of PMMA was also investigated. A shift towards higher glass transition temperatures and slight improvements in thermal stability of the nanocomposites compared to pure PMMA were observed and are discussed herein.

Structural and optical investigation of gadolinia-doped ceria powders prepared by polymer complex solution method

Abstract We present a polymer complex solution method using a modified combustion synthesis procedure, for the production of well crystalline, sub-micron gadolinia-doped ceria powders of Ce0.9Gd0.1O1.95 composition. Polyethylene glycol of two different molecular weights (200 and 20000) was used as both fuel for the combustion and nucleating agent for the crystallization process. The synthesized materials were characterized using X-ray diffraction, thermal analysis, scanning electron microscopy, and optical and photoluminescence spectroscopy. The powders are quite similar, fully crystallized in a cubic fluorite-type phase with average crystallite size of about 70 nm and average particle size in the range 220–240 nm. UV-vis absorption spectra show the absorption edge at 3.26 eV. The presence of oxygen vacancies, confirmed indirectly by clear violet emission observed at 428 nm, originated from the 5D1 → 4F1 transition of Ce3+ions.

Processing and characterization of up-converting Er3+ doped (Lu0.5Y0.5)2O3 nanophosphor

Abstract In this paper we demonstrate visible up-conversion emission of Er3+ doped (Lu0.5Y0.5)2O3 nanophosphor and discuss possible mechanisms for pumping the upper energy levels of Er3+ ions. Polymer complex solution synthesis yields well crystalline, pure-phase cubic nanopowder with particle size in the 20–50 nm range. Red, green and blue up-conversion emission is measured under near-infrared excitation (1 540 nm), over the temperature range 10–300 K. The red/green intensity ratio indicates that the mechanism responsible for populating red up-conversion is temperature dependent. Decay times are found to be around 0.25 ms for red and green, and around 70 μs for blue emission.

Structural characterization of erbium doped LAS glass ceramics obtained by glass melting technique

Samples of transparent glass-ceramics in the ternary system Li2O-Al2O3-SiO2 (LAS), with Er2O3 as a luminescent dopant, are investigated. The initial glass is obtained by the classical melting technique. In order to induce ceramization of the glass, TiO2 and ZrO2 are added in small amount as nucleating agents. The thermal treatments at 730 and 770°C are carried out to promote formation of titanium zirconate solid solution precipitates. The spatial distribution of the precipitates in the material, their morphology, and their composition are investigated with TEM, HRTEM, HAADF-STEM, EELS and EFTEM. The results demonstrate that with the glass-melting preparation technique it is possible to achieve small nanoparticles with uniform distribution and higher number density than with the sol-gel glass preparation.