Modification of structural, morphological and optical properties of anatase TiO2 nanoparticles doped with trivalent rare-earth ions.

U ovoj doktorskoj disertaciji prikazana je temeljna studija modifikovanja strukturnih, morfoloških i optičkih svojstava anatas TiO2 nanočestica dopiranjem trovalentnim jonima retkih zemalja: prazeodijuma, neodijuma, samarijuma, europijuma, disprozijuma, terbijuma, holmijuma, erbijuma i tulijuma, pri koncentraciji od 1 at.%. Pomenuti materijali sintetisani su sol-gel tehnikom i žareni na temperaturi od 420 ºC. Strukturna svojstva nedopiranog anatas TiO2 kao i TiO2 dopiranоg jonima retkih zemalja ispitivana su rendgenskom difrakcionom analizom. Utvrđeno je da se sol-gel sintezom dobijaju čiste anatasne kristalne strukture sa veličinom kristalita od svega nekoliko nanometara. Uticaj jona retkih zemalja u anatasnoj kristalnoj strukturi titan-dioksida ogleda se u značajnom porastu specifične površine čestica. Takođe, sintetisani su nanoprahovi TiO2 koloidnom tehnikom u cilju korelisanja različitih metoda sinteza sa strukturnim, morfološkim i optičkim svojstvima...The primary aim of this thesis is to explain the modification of structure, morphology and optical properties of anatase TiO2 nanoparticles doped with trivalent rare-earth ions: praseodymium, neodymium, samarium, europium, terbium, dysprosium, holmium, erbium, and thulium, with the concentration of 1 at.%. These materials were synthesized by the sol-gel technique and further annealed at 420 °C. Structural properties of anatase TiO2 and TiO2 doped with trivalent rare-earth ions are studied by X-ray diffraction analysis. It was confirmed that pure anatase TiO2 with the crystallite size of only a few nanometers was obtained by sol-gel synthesis. The incorporation of rare earth ions in the anatase TiO2 is reflected in the significant increase of the specific surface area of TiO2 nanopowders doped with rare-earth ions in comparison with undoped TiO2. Also, the TiO2 nanopowders were synthesized by a colloid technique to correlate the different methods of synthesis with structural, morphological and optical properties..

Evaluation of Staining-Dependent Colour Changes in Resin Composites Using Principal Component Analysis

Colour changes in Gradia Direct (TM) composite after immersion in tea, coffee, red wine, Coca-Cola, Colgate mouthwash, and distilled water were evaluated using principal component analysis (PCA) and the CIELAB colour coordinates. The reflection spectra of the composites were used as input data for the PCA. The output data (scores and loadings) provided information about the magnitude and origin of the surface reflection changes after exposure to the staining solutions. The reflection spectra of the stained samples generally exhibited lower reflection in the blue spectral range, which was manifested in the lower content of the blue shade for the samples. Both analyses demonstrated the high staining abilities of tea, coffee, and red wine, which produced total colour changes of 4.31, 6.61, and 6.22, respectively, according to the CIELAB analysis. PCA revealed subtle changes in the reflection spectra of composites immersed in Coca-Cola, demonstrating Coca-Colas ability to stain the composite to a small degree

Modification of structural, morphological and optical properties of anatase TiO2 nanoparticles doped with trivalent rare-earth ions.

U ovoj doktorskoj disertaciji prikazana je temeljna studija modifikovanja strukturnih, morfoloških i optičkih svojstava anatas TiO2 nanočestica dopiranjem trovalentnim jonima retkih zemalja: prazeodijuma, neodijuma, samarijuma, europijuma, disprozijuma, terbijuma, holmijuma, erbijuma i tulijuma, pri koncentraciji od 1 at.%. Pomenuti materijali sintetisani su sol-gel tehnikom i žareni na temperaturi od 420 ºC. Strukturna svojstva nedopiranog anatas TiO2 kao i TiO2 dopiranоg jonima retkih zemalja ispitivana su rendgenskom difrakcionom analizom. Utvrđeno je da se sol-gel sintezom dobijaju čiste anatasne kristalne strukture sa veličinom kristalita od svega nekoliko nanometara. Uticaj jona retkih zemalja u anatasnoj kristalnoj strukturi titan-dioksida ogleda se u značajnom porastu specifične površine čestica. Takođe, sintetisani su nanoprahovi TiO2 koloidnom tehnikom u cilju korelisanja različitih metoda sinteza sa strukturnim, morfološkim i optičkim svojstvima...The primary aim of this thesis is to explain the modification of structure, morphology and optical properties of anatase TiO2 nanoparticles doped with trivalent rare-earth ions: praseodymium, neodymium, samarium, europium, terbium, dysprosium, holmium, erbium, and thulium, with the concentration of 1 at.%. These materials were synthesized by the sol-gel technique and further annealed at 420 °C. Structural properties of anatase TiO2 and TiO2 doped with trivalent rare-earth ions are studied by X-ray diffraction analysis. It was confirmed that pure anatase TiO2 with the crystallite size of only a few nanometers was obtained by sol-gel synthesis. The incorporation of rare earth ions in the anatase TiO2 is reflected in the significant increase of the specific surface area of TiO2 nanopowders doped with rare-earth ions in comparison with undoped TiO2. Also, the TiO2 nanopowders were synthesized by a colloid technique to correlate the different methods of synthesis with structural, morphological and optical properties..

Non-isothermal crystallization kinetics of Y(2)Ti(2)O7

The crystallization kinetics of Y2Ti2O7 powders prepared by a Pechini-type polymerized complex route was studied using differential thermal analysis under non-isothermal conditions. Apparent activation energies of crystallization of 816 and 804 kJ mol(-1) were obtained from calculations based on the Arrhenius equation and isoconversional analysis, respectively. The crystallization kinetics followed the so-called A3 model, as confirmed using several criteria, namely, the Malek, master plot, and Perez-Maqueda Methods. The measurement results and calculated crystallization parameters (n = 3, m = 2) showed that the crystallization process includes a constant rate of nucleation and two-dimensional growth of nuclei, and excluded the possibility of surface crystallization

Effects of Li+ co-doping on properties of Eu3+ activated TiO2 anatase nanoparticles

Sol-gel technique for the synthesis of anatase TiO2 at 420 degrees C produces nanocrystals of 10-20 nm in size with Ti4+ in crystal volume and Ti3+ at terminal planes of the crystal. The study of Li+ co-doping effects on the structure, morphology, absorption, and luminescence of Eu3+ activated TiO2 anatase nanocrystals is presented. Pure anatase structure is achieved up to 9 at.% Li, with significant improvement in crystallinity of europium doped anatase TiO2. The Li+ co-doping reduces the unit cell volume of the crystal, induces the blue shift of the absorption edge, lengthens the lifetime of Eu3+ D-5(0) excited state, and improves the Eu3+ emission intensity up to 37.5%. Judd-Ofelt analysis of Eu3+ emission showed enhancement of quantum efficiency from 66.4% to 98.7% when TiO2:Eu3+ was co-doped with 9 at.% of Li. (C) 2017 Elsevier B.V. All rights reserved

The influence of gamma irradiation on the color change of wool, linen, silk, and cotton fabrics used in cultural heritage artifacts

Fabrics made of wool, linen, silk, and cotton, which are used in the making of artifacts of cultural heritage, were divided into three groups. The first group wasn't dyed, the second group was dyed with natural dye (using sour cherry), and the third one was dyed with artificial aniline dye. For the conservation purposes, all samples were exposed at ambient temperature to gamma radiation doses, from 0.5 to 25 kGy, using a Co-60 irradiator. The influence of gamma irradiation treatment on the color changes was investigated. The obtained results revealed that the irradiation affects the color changes in all samples. All samples became more or less darker under the influence of gamma irradiation. This change in darkness is most pronounced in samples dyed with natural colors. Also, the highest differences in color change and darkness were observed in linen samples. © 2018 Elsevier Lt

Non-isothermal crystallization kinetics of the heavy-group lanthanide dititanates

The systematic investigation of crystallization kinetics of heavy-group lanthanide dititanate pyrochlores, HL2Ti2O7 (HL=Lu, Tm, Er, Ho, Y, Dy, and Tb) is presented. Materials are prepared by the Pechini-type polymerized complex route, and their thermal properties were studied by differential thermal analysis under non-isothermal conditions. For this group, the crystallization temperature became larger with increasing the ionic radius of lanthanides, from 1066 K for Lu2Ti2O7 to 1125 K for Tb2Ti2O7. The linear dependence of crystallization temperature on radius of heavy lanthanide ions is found to follows T-c [K] = 168.86 + 920.89 x r(ion) [angstrom] semi-empirical equation. Apparent activation energies of crystallization were obtained from calculations based on the Arrhenius equation, isoconversional method and PerezMaqueda method, and are similar to 805 kJ mol(-1) calculated by three different methods. The crystallization kinetics followed the so-called Avrami Erofeev (A3) model, as confirmed using several criteria, namely, the Malek, master plot, and Perez-Maqueda methods. The crystallization mechanism of all lanthanide dititanate pyrochlores is found to be the same, and the crystallization process involves a constant rate of nucleation and two-dimensional growth of nuclei. (C) 2017 Elsevier B.V. All rights reserved.6th International Conference of Excited States of Transition Elements (ESTE) / Workshop on Luminescence, Aug 21-26, 2016, Polanica Zdroj, Polan

Li1.8Na0.2TiO3:Mn4+: The highly sensitive probe for the low-temperature lifetime-based luminescence thermometry

In this work, the potential of Li1.8Na0.2TiO3:Mn4+ for the lifetime-based luminescence thermometry is assessed. The material is prepared by the solid-state reaction of Li2CO3, Na2CO3, and nanostructured TiO2 at 800 °C, and its monoclinic structure (space group C2/c) is confirmed by X-ray diffraction analysis. In this host, Mn4+ provides strong absorption around 330 nm and 500 nm due to 4A2g → 4T1g and 4A2g→ 4T2g electric dipole forbidden and spin-allowed electron transitions, respectively, and emits around 679 nm on account of 2Eg→ 4A2g spin forbidden electron transition. Temperature dependences of emission intensity and emission decay are measured over the 10–350 K range. Due to the low value of energy of 4T2g level (20000 cm−1), the strong emission quenching starts at low-temperatures which favors the use of this material for the luminescence thermometry. It is demonstrated that the quite large value of relative sensitivity (2.27% K−1@330 K) facilitates temperature measurements with temperature resolution better than 0.15 K, and with the excellent repeatability. © 2019 Elsevier B.V

Organic solvent-assisted co-precipitation synthesis of red-emitting K2TiF6:Mn phosphors with improved quantum efficiency and optimized morphology

We report an organic solvent–assisted (OSA) co-precipitation strategy for the production of Mn4+-activated K2TiF6 phosphor. The phosphor particle size was controlled through the selection of organic solvents with an alcohol functional group and different carbon chain lengths used in the synthesis. The synergistic effect of the organic solvent and hydrofluoric acid results in large smoothed hexagonal-shaped crystal sheets of particles that become larger as the carbon chain length of the organic solvent increases. The photoluminescence (PL) properties of K2TiF6:Mn powders strongly depend on the size and thickness of the particles. The addition of n-butanol during the synthesis increases the emission intensity of K2TiF6:Mn by 208%. The PL quantum efficiency of phosphors prepared using the n-butanol-assisted strategy is much higher (98.2%) than that of conventionally prepared phosphors (89.9%). Our findings demonstrate a way to prepare the K2TiF6:Mn phosphor with targeted morphology and very high quantum efficiency and also provide the route for the optimization of all Mn4+-activated fluoride phosphors used in white light-emitting diodes

Visible light absorption of surface modified TiO2 powders with bidentate benzene derivatives

TiO2 powders with different specific surface area were prepared using reproducible, sol gel synthetic route and their ability to form hybrids with catechol and 5-amino salicylic acid was compared with the commercially available Degussa P25 TiO2 powder. Microstructural characterization involving transmission electron microscopy, X-ray diffraction analysis and nitrogen adsorption-desorption isotherms indicated that TiO2 samples cover reasonably wide size and/or specific surface area range (50-115 m(2)/g). The surface modification of TiO2 powders with catechol and 5-amino salicylic acid induced significant shift of absorption to the visible spectral region due to charge transfer complex formation. It should be emphasized that tunable optical properties of TiO2 in powder form have never been reported in the literature. The largest red shift of the absorption onset was observed for sample with the largest specific surface area upon surface modification with both ligands. The binding of the modifier molecules to the surface Ti atoms was studied using Fourier transform infrared spectroscopy. (C) 2015 Elsevier Inc. All rights reserved