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Monosized Up-Converting NanoParticles (UCNPs) with biocompatible surface and unique optical properties attract a great interest as new cell markers or drug delivery systems. The uppermost UC efficiency of β-NaYF4:Yb/Er phase is due to its hexagonal P63/m space group arrangement which could accommodate higher concentration of dopants at shorter distance. Stabilization of this phase in nanoparticles is usually achieved through thermal decomposition of organic precursors in the presence of solvents with a high boiling point. Here, for the same purpose, we used gadolinium co-doping during chitosan assisted solvothermal processing of inorganic precursor salts. Precursor concentration, solvent type, and synthesis time were varied in order to determine their influence on the β-NaY0.65Gd0.15F4:Yb0.18Er0.02 phase crystallization. The XRPD analysis showed that lower surplus of fluoride ions during synthesis leads to formation of Y0.65Gd0.15F4:Yb0.18Er0.02 orthorhombic phase, while the increase of fluoride content or prolongation of the processing time enhances formation α- NaY0.65Gd0.15F4:Yb0.18Er0.18 phase. Along with it, the changes of UCNPs morphology from spindle to spherical shape is detected. All samples emit intense green emission due to the (2H11/2, 4S3/2) → 4I15/2 electronic transitions, after been excited with infrared light (λ=978 nm).

Up-Converting NanoParticles (UCNPs) with biocompatible surface and unique optical properties, low phonon energy (350 cm-1) and high chemical stability attract a great interest as potential biomarkers or drug delivery systems. The hydro/solvo thermal method, as one of the most economical method which do not include the use of toxic precursors, was applied here for the synthesis of NaY0.65Gd0.15F4:Yb,Er nanoparticles at 200oC. Chitosan is used as surfactant and structural directing agent. In addition, different processing parameters (precursor concentration, solvent type, and synthesis time) were applied to investigate their influence on the structural, morphological, and optical properties of UCNP. The XRD analysis showed that with a smaller surplus of fluoride ions the formation of Y0.65Gd0.15F4:Yb,Er orthorhombic phase occurs, while the increase of fluoride content or reaction time leads to NaY0.65Gd0.15F4:Yb,Er cubic phase formation. Along with it, the changes of UCNPs morphology from spindle to spherical shape is detected. All samples emit intense green emission due to the (2H11/2, 4S3/2) → 4I15/2 electronic transitions, after been excited with infrared light (λ=978 nm).

Up-converting nanoparticles (UCNPs) with unique ability to convert NIR to VIS light (anti-Stokes process) have a wide application in optoelectronics, forensic, security labeling and biomedicine. Over the past few years different methods (like co-precipitation, thermal decomposition, hydro/solvothermal synthesis, etc.) are used for synthesis of β-NaYF4: Yb/Er phase, mainly from toxic organic precursors. In this work we explore conditions for stabilization of β-NaYF4: Yb/Er phase in nanoparticles applying sonochemistry synthesis of common inorganic precursor. The XRPD analysis showed that pure β phase is possible to obtained after 120 min of ultrasonification, while for shorter processing time (30-90min), cubic α-NaYF4: Yb/Er or orthorhombic YF3 : Yb,Er phase were founded too. The SEM and TEM analysis reveal presence of elongated nanoparticles self-assembled in spindles long up to 500 nm. Evolution of particle morphological and particle composition are analysed and correlated further with intensity of green emission (2H11/2,4S3/2→4I15/2) intensity measured under excitation of 978 nm.

Up-conversion is the optical property of materials which have ability to convert low energy photons (usually from infrared spectrum) into higher energy photons (from visible spectrum). Such compounds, usually lanthanide doped oxides or fluorides, have many applications in photoluminescence science and technology today. Currently, (β) NaYF4:Yb,Er polymorph is considered to be the most efficient up-converting material. Its synthesis usually includes the usage of toxic solvents, long-term heating, high pressures, controlled gas atmosphere, etc. The aim of this work was to utilize rarely applied sonochemical synthesis for the stabilization of (β) NaYF4:Yb,Er phase under mild and environmental friendly conditions. For this purpose, we performed ultrasonic treatment of common nitrate precursors and sodium fluorine for a different time. The obtained powders were analyzed in order to determine their phase composition and thermal stability, morphology, dopants distribution, particles surface purity and luminescent characteristics. Owing to this, the chemical and crystal phase transformations that occurred in specified periods of synthesis time are explained in detail. Moreover, it was shown that obtaining of uniformly doped (β) NaYF4:Yb,Er mosocrystalline particles is possible after 2h of sonication.

The Nonlinear Laser Scanning Microscopy (NLSM) contributes to the cell labeling through addressing two main issues: photobleaching and phototoxicity. Moreover, an increase of the penetration depth and a reduction of background autofluorescence are achieved.We have used a multidisciplinary approach combining expertise in material science, nanoparticles synthesis and characterization, cancer cell and tissue labeling, and high resolution imaging, in order to accomplish in vitro imaging of the cancer cells. We have imaged the oral squamous carcinoma cells and human gingival cells. We have demonstrated that we are able to take high contrast images. We have shown position of the nanoparticles in cells, through colocalization of the cell auto-fluorescence and the nanoparticles up-conversion.We plan to improve our abilities through further optimization of the up-converting nanoparticles (smaller and brighter particles) and microscopy technique.

Magnesium aluminate and other alumina-based spinels attract attention due to their high hardness, high mechanical strength, and low dielectric constant. MgAl2O4 was produced by solid-state reaction between MgO and α-Al2O3 powders. Mechanical activation of 30 minutes in a planetary ball mill was used to increase the reactivity of powders. Yttrium oxide and graphene were added to prevent abnormal grain growth during sintering. Samples were sintered by hot-pressing under vacuum at 1450 °C. Phase composition and microstructure of sintered specimens were characterized by X-ray diffraction analysis and scanning electron microscopy. Rietveld analysis revealed 100 % pure spinel phase in all sintered specimens, and decrease in crystallite size with the addition of yttria or graphene. Density measurements indicated that the mechanically activated specimen reached 99.6 % relative density, while other specimens were above 96.5 % relative density. Furthermore, the highest solar absorbance and highest spectral selectivity as a function of temperature were detected for the mechanically activated specimen with graphene addition. Mechanical activation is an efficient method to improve the densification behaviour of MgAl2O4 produced from mixed oxide powders, while additives improve microstructure and optical properties.

U ovom radu je opisano tretiranje tekstilne boje "Reactive black 5" poroznim elektrodama naprevljenim od korišćenog grafita koje sadrže različite udele cerijuma.

Europium doped mayenite (C12A7) powders of different concentrations (0.5, 1.0, 1.5, and 2.0 at.%) have been synthesized by a modified glycine/nitrate procedure - MGNP). Obtained samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE- SEM), and steady-state photoluminescence spectroscopy. The effect of doping concentration on photoluminescence properties of Eu3+ doped mayenite was studied and discussed. With the increasing of Eu3+ doping concentration, the red-emitting intensity exhibited behavior that increased firstly and then decreased. The optimal Eu3+ ion concentration is found to be 1.5%. High-pressure luminescence was measured in a Betsa high-pressure membrane diamond anvil cell up to 23 GPa.

Hydroxyapatite (HAp) has been widely used as bone reconstruction materials due to their similarity to bone tissue. The improvement of HAp properties was achieved by doping its crystal lattice with different ions. Lanthanides, i.e. Rare Earth Elements (RE) are also suitable for doping HAp. The aim of the presented research was to investigate the possibility of creating lumino-magnetic particles of HAp doped with gadolinium (Gd3+) ions and co-doped with ytterbium/thulium (Yb3+/Tm3+) or europium (Eu3+) ions for potential use in multimodal imaging (MI). Pure HAp (Ca5(PO4)3(OH)), magnetic HAp:Gd (Ca4.85Gd0.15(PO4)3(OH)), and lumino-magnetic HAp:Gd/Yb/Tm (Ca4.85Gd0.03Yb0.1Tm0.02(PO4)3(OH)) and HAp:Gd/Eu (Ca4.94Gd0.02Eu0.04(PO4)3(OH)) particles were synthesized using emulsification process and hydrothermal processing. All synthesized particles had an elongated shape and exhibited a paramagnetic behavior. Reduction of the unit cell volume as a result of replacement of Ca2+ ions by ions with a smaller ionic radius (Gd3+, Yb3+, Tm3+, Eu3+) confirmed by using XRD and Rietveld refined plots. The energy band gap values of the synthesized samples range from 4.93 to 3.18 eV and decrease in the following order: HAp:Gd >HAp>HAp:Gd/Eu>HAp:Gd/Yb/Tm. The results of photoluminescence emission spectra of HAp:Gd/Yb/Tm and HAp:Gd/Eu particles showed characteristic transitions of Tm3+ and Eu3+, respectively.

There is a great interest for the synthesis of rare earth (RE) doped up-converting nanoparticles (UCNPs) which morphological and luminescence properties are well suited for application in optoelectronics, forensics, security and biomedicine. The synthesis of such particles usually comprises decomposition of organometallic compounds in an oxygen-free environment followed with coating of biocompatible layer or ligands exchange. In this work hydroxyl-carboxyl (HO-C) type of chelators (citric acid and sodium citrate) are used for the stabilization of NaYF4:Gd,Yb,Er UCNPs during solvothermal treatment of rare earth nitrate salts with different fluoride sources (NaF, NH4F and NH4HF2). The x-ray powder diffraction (XRPD) showed that all powders contain the mixture of cubic and hexagonal NaYF4:Gd,Yb,Er phase in nano and micro-sized particles respectively. However, the content of later one prevails in samples obtain when Nacitrate is used as chelator, regardless of which fluoride source is used for precipitation. Additionally, variation of the particles size and shape is detected with a variation of fluoride type. All particles have hydrophilic surface due to retention of citrate ligands and emit intense green light emission centered at 519 and 539 nm (2H11/2,4S3/2→4I15/2) when excited with near infrared light.

application as lasers, displays, photo-thermal agents and biomarkers. Due to efficient two-phonon excitation and the large anti-Stocks shift UCNPs are able to emit visible or UV photons under excitation by near-infrared (NIR). Over the last decade, decomposition of organometallic compounds has been indicated as one of the most convenient method for the synthesis of monodisperse NaYF4:Yb3+,Er3+ UCNPs with a hexagonal crystal structure. Herein, NaY0.8-xGdxYb0.18Er0.02F4 (x= 0.3 or 0.15) up-conversion nanoparticles crystallized in the hexagonal space group P63/m were successfully synthesized solvothermally utilizing rare earth nitrates, NaF and polyvinylpyrrolidone (PVP) in ethanol-water mixture at 200 °C. Rietveld refinement of the X-ray powder diffraction (XRPD) data and high resolution transmission microscopy (HRTEM) analysis show that all UCNPs are monocrystalline (60-70 nm), have low defect concentration and uniform dopants distribution. Fourier-transform infrared (FTIR) spectroscopy indicate existence of the PVP ligands at the UCNPs surface, while photoluminescence (PL) spectra shows characteristic green (at 520 and 540 nm, due to 2H11/2, 4S3/2→4I15/2 transitions) and red (at 655 nm, due to 4F9/2 → 4I15/2 transition) emission lines under excitation by NIR (λ =980 nm) light.

Thanks to the unique optical properties, up-converting nanoparticles (UCNPs) have a wide application in optoelectronics, forensics, security and biomedicine. The synthesis of the most efficient hexagonal β-NaYF4: Yb/Er phase is usually performed through thermal decomposition of organic precursors which could cause the UCNP cytotoxicity. Since cubic polymorph is kinetically more stable than hexagonal, we used citric acid and Na-citrate for the nucleation of hexagonal NaYF4: Yb, Er phase in nanosized particles. Additionally, effect of different precipitation agents (NaF, NH4F and NH4HF2) used during solvothermal synthesis is explored. The XRPD analysis showed that using of citric acid led to a product composed from mixture of cubic and hexagonal NaYF4: Yb/Er phase, while the presence of Na-citrate influences the nucleation of well crystallized hexagonal β-NaYF4: Yb/Er phase, regardless of precipitation agents used. All samples are composed of polycrystalline spherical particles which size is influenced by the precursor chemistry. UCNPs emit intense green emission due to the (2H11/2, 4S3/2) → 4I15/2 electronic transitions, after been excited with infrared light (λ=978 nm).

During the last decade zinc oxide (ZnO) has attracted considerable attention as a promising material for electronic, optoelectronic and spintronic devices. ZnO has a wide bandgap (3.37 eV at room temperature) and relatively large exciton binding energy (60 meV) which enables multifunctional application. Until now ZnO-based materials have been used as UV and blue light emitters, varistors, thermistors, semiconductors, photoanodes, and other. Various approaches have been applied to improve functional properties of zinc oxide, such as: fabrication of ZnO-based heterojunction particles, particles’ surface sensitization, hydrogenation, etc. It has been found that intrinsic defects (vacancies, interstitials and antisites) in the crystal structure of a ZnO strongly influenced its electrical and optical properties. Thus, correlation of the intrinsic defects concentration with optical and electrical properties of ZnO materials is of great importance for their further application in opto-electronic devices. In this study we investigated the influence of intrinsic defects concentration on the optical, electrical and photoelectrocatalytic properties of ZnO materials. To obtain ZnO powder with a high concentration of intrinsic defects microwave processing of precipitate was employed, while for further varying of defects concentration, the powder was thermally treated in three different atmospheres: air, argon and oxygen. The ZnO powder was uniaxially pressed (P = 100 MPa) in cylindrical compacts (R= 6 mm and h approx. 3 mm) which were sintered in different atmospheres by heating rate of 10 °/min up to 1100 °C, and with dwell time of 1 h. To study a crystal structure of ZnO samples XRD and Raman spectroscopy were used, while for microstructural investigation field emission scanning electron micrographs were recorded. Optical properties were studied using UV–Vis diffuse reflectance spectroscopy. To reveal the role of intrinsic defects in ZnO crystal lattice on functional properties, XPS, photoluminescence, electroluminescence and electrochemical impedance spectra were analyzed. A detailed analysis of the experimental results imply that a high concentration of intrinsic defects, in particular oxygen vacancies, is of the greatest importance for tunable light-emitting diode application and significant for the photoanode properties. To support our experimental observation we performed ab initio calculations based on density functional theory (DFT).

There is a growing interest for development of a facile and reproducible approach for the synthesis of biocompatible lanthanide doped up-converting nanoparticles (UCNPs) for deep tissue imaging and targeted drug delivery. Synthesis of such particles is usually performed through the decomposition of organometallic compounds, followed either with a ligands exchange or with a biocompatible layer coating. In this work, biocompatible NaYF4:Yb,Er (17 mol% Yb; 3 mol% Er) nanoparticles were synthesized by one-pot hydrothermal processing with an assistance of chitosan (Ch) or polyacrylic acid (PAA). Obtained powders were analyzed by X-ray powder diffraction (XRPD, Bruker D8 Discovery), field emission scanning electron microscopy (FE-SEM, Zeiss, DSM 960), transmission electron microscopy (TEM, JEOL JEM 2010), Fourier transform infrared (FTIR, Thermo Scientific Nicolet 6700) and photoluminescence (PL, Spex Fluorolog with C31034 cooled photomultiplier) spectroscopy. The results showed that although both powders crystallize in the same crystal arrangement (cubic, Fm-3m), particles size, shape and optical properties are dependent on the polymer used.

Rare earth ions (RE3+) are highly sensitive to local symmetry so changing the symmetry is reflected in their luminescence spectra. In this work we investigated the high pressure photoluminescence properties of cubic and monoclinic Y2O3, as well as, monoclinic Y2MoO6, doped either with Eu3+ or Sm3+ ions. Photoluminescence emission of cubic Y2O3 :Sm3+ and Y2O3 :Eu3+ phases were recorded up to the pressure of 20 GPa and 15 GPa, respectively. With varying pressure, the intensity ratio of 4G5/2 → 6H7/2 and 4F3/2 → 6H7/2 Sm3+ emission shows three distinct regions. Furthermore, the intensity ratio of 5D0 → 7F1 and 5D0 → 7F2 Eu3+ emission of the cubic matrix has similar pressure dependence as Sm3+ doped phase. A steep pressure dependence evident in the range of 9.2-13.1 GPa could be used for detecting a pressure induced cubic to monoclinic phase transition of Y2O3 matrix. It matches well the behavior of the pressure sensitive Sm3+ spectra in the range of 9.1-11.6 GPa, which is proven to appear due to a phase transition at ~ 11 GPa. The monoclinic Y2O3 :Eu3+ also has a pressure-sensitive intensity ratio of 5D0→7F1 and 5D0→7F2 emission lines. Measurements for the monoclinic Y2O3 :Eu3+ matrix were recorded up to 8 GPa. The dependence is unambiguous, without any phase transitions in the measured region. The nature and high sensitivity suggests that this dependence can be used as an efficient high pressure sensor. Photoluminescence emission measurements of Y2MoO6:Sm3+ and Y2MoO6:Eu3+ phases were recorded up to 12 and 11.5 GPa, respectivelly. Intensity ratio variation of 4G5/2→6H5/2 and 4G5/2→6H7/2 Sm3+ emission lines, as well as of 5D0 → 7F1 and 5D0 → 7F2 Eu3+ emission lines as a function of pressure can be also used for detection of the Y2MoO6 phase transition. The accomplished results demonstrate the properties of Y2MoO6:Sm3+ and Y2MoO6:Eu3+ inorganic phosphors, with emmision linear dependance of the intensity ratio on the pressure up to 8 GPa, could be used as an efficient high pressure sensor. VII Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 17-19, 2018; Belgrade

There is a growing interest for development of a facile and reproducible approach for the synthesis of biocompatible lanthanide doped up-converting nanoparticles (UCNPs) for deep tissue imaging and targeted drug delivery. Synthesis of such particles is usually performed through the decomposition of organometallic compounds, followed either with a ligands exchange or with a biocompatible layer coating. In this work, biocompatible NaYF4:Yb,Er (17 mol% Yb; 3 mol% Er) nanoparticles were synthesized by one-pot hydrothermal processing with an assistance of chitosan (Ch) or polyacrylic acid (PAA). Obtained powders were analyzed by X-ray powder diffraction (XRPD, Bruker D8 Discovery), field emission scanning electron microscopy (FE-SEM, Zeiss, DSM 960), transmission electron microscopy (TEM, JEOL JEM 2010), Fourier transform infrared (FTIR, Thermo Scientific Nicolet 6700) and photoluminescence (PL, Spex Fluorolog with C31034 cooled photomultiplier) spectroscopy. The results showed that although both powders crystallize in the same crystal arrangement (cubic, Fm-3m), particles size, shape and optical properties are dependent on the polymer used.

Composite biomaterials based on nano hydroxyapatite (HAp) are the subject of numerous studies in reconstructive medicine. Multifunctional and nanoparticulate systems based on HAp and biodegradable polymers are successfully designed as systems for controlled and systemic drug delivery suitable for use in reconstructive medicine. Thanks to the stability and flexibility of the apatite structure, Ca ions can be replaced with various elements (Zn, Sr, Mg, Co, etc.). Doping the apatite structure enables potential application of this material in preventive medicine, too. Multimodal imaging (MI) is a new and promising technique for improved diagnosis and it is patient-friendly because it saves time. MI has recently attracted much attention due to the advantageous combination of various imaging modalities, such as computer tomography (CT), photoluminescence (PL) and magnetic resonance imaging (MRI). For such a promising approach, we devised new multimodal contrast agents using the doping of a HAp matrix with rare earth (RE) ions. Pure HAp (Ca5(PO4)3(OH)), magnetic HAp:Gd (Ca4.85Gd0.15(PO4)3(OH)), down-converting HAp:Gd,Eu (Ca4.94Gd0.02Eu0.04(PO4)3(OH)) and up-converting HAp:Gd,Yb/Tm (Ca4.85 Gd0.03Yb0.1Tm0.02(PO4)3(OH)) were synthesized using a hydrothermal procedure. Morphological and structural characteristics of the particles were obtained using X-ray powder diffraction (XRPD), scanning and transmission electron microscopy (SEM/TEM), energy dispersive X-ray spectrometry (EDX), photoluminescence (PL), Fourier Transform Infrared (FTIR) and diffuse reflectance spectroscopy (DRS). The results show that needle-like nano- or microparticles were obtained in all systems. Their phase composition and uniform distribution of dopants were confirmed by the structural refinement of the XRPD data, change in the band gap, and luminescence spectra recorded using different excitation sources (λ= 370, 394 and 977 nm). Poster: [https://hdl.handle.net/21.15107/rcub_dais_4064]