Rare Earth‐Doped Anatase TiO2 Nanoparticles

Titanium dioxide is a wide band‐gap semiconductor of high chemical stability, nontoxicity and large refractive index. Because of the high photocatalytic activity, anatase is a preferred TiO2 form in many applications such as for air and water splitting and purification. Doping of TiO2 with various ions can increase the photocatalytic activity by enhancing light absorption in visible region and can alter structure, surface area and morphology. Also, by doping TiO2 with optically active ions, visible light via up‐ or downconversion luminescence can be produced. It is a challenge to optimize the synthesis procedure to incorporate rare earth RE3+ ions into the TiO2 structure due to large mismatch in ionic radii between the Ti4+ and RE3+ and because of the charge imbalance. Visible (VIS) and ultraviolet (UV) luminescence of several RE3+ ions can be obtained when incorporated into anatase TiO2, also affecting microstructural characteristics of TiO2. It is of great importance to summarize publications on rare earth‐doped anatase TiO2 nanoparticles to find correct TiO2-RE combination to sensitize trivalent rare earths luminescence, as well as to predict or tune structural and morphological properties. A better understanding on these topics may progress the desired design of this kind of material towards specific applications

High resolution luminescence spectroscopy and thermoluminescence of different size LaPO4:Eu3+ nanoparticles

T. G. acknowledges the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 (1.1.1.2/16/I/001). K. S. and K. L. acknowledge the Latvian National Research Program IMIS2. The authors from Vinča Institute of Nuclear Sciences acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Project No: 45020 and 172056 ).Nanoparticles (5 nm) and nanorods (2 nm × 15 nm and 4 nm × 20 nm) of monoclinic monazite LaPO4:Eu3+ were prepared by reverse micelle and co-precipitation techniques. Effects of the particle size and surface defects on the intensity of luminescence and the emission spectrum shapes were analyzed by high resolution spectroscopy under laser (266 nm) and X-rays excitation. All synthesized LaPO4:Eu3+ samples showed similar spectral features with characteristic Eu3+ ions emission bands: 5D0→7F0 centered at 578.4 nm, magnetic-dipole transition 5D0→7F1 at 588–595 nm, electric-dipole transition 5D0→7F2 at 611.5–620.5 nm, 5D0→7F3 at (648–652 nm) and 5D0→7F4 at (684–702.5 nm), with the most dominant electric-dipole 5D0→7F2 transition. Additionally, the thermally stimulated luminescence was studied for the most dominant peak at 611.5 nm. It was shown that the Eu3+ doping creates traps in all samples. Two prominent and well resolved glow peaks at 58.7 K and 172.3 K were detected for 5 nm nanoparticles, while low-intensity glow-peaks at 212.1 K and 212.2 K were observed in the X-rays irradiated nanorods. Displayed glows could be attributed to free and bound electrons and holes or to the recombination of electrons of ionized oxygen vacancies with photogenerated holes. To obtain information about the processes and specific defect type it is necessary to carry out additional analysis for all synthesized samples. The glow curves were analyzed and trap parameters were estimated and discussed throughout the paper.ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 (1.1.1.2/16/I/001); IMIS2; Ministry of Education, Science and Technological Development of the Republic of Serbia (Project No: 45020 and 172056 ); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Up-conversion luminescence of GdVO4:Nd3+/Er3+ and GdVO4:Nd3+/Ho3+ T phosphors under 808 nm excitation

All authors acknowledge to the COST Action CM1403: The European upconversion network - from the design of photon-upconverting nanomaterials to biomedical applications (2014–2018). The authors from the University of Belgrade acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Project Nos. 45020 and 172056 ). K. S. acknowledges the Latvian National Research Program IMIS2 (Grant No. 302/2012 ). T. G. acknowledges the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 ( 1.1.1.2/16/I/001 ).In recent years, there exists a tendency in research of up-conversion materials to shift excitation from 980 nm to shorter wavelengths. Here, in order to produce up-conversion luminescence emission of GdVO4-based materials under 808 nm excitation, polycrystalline powders of GdVO4:Er3+/Nd3+ and GdVO4:Ho3+/Nd3+ were successfully prepared by a high-temperature solid-state reaction technique. The prepared powders were highly crystalline with a single-phase zircon-type GdVO4 structure and consisted of micrometer-sized irregular spherical particles (2–6 μm in diameter). In all studied samples, visible up-conversion luminescence was successfully achieved under 808 nm illumination. Near-infrared pumping produced emission bands in the green, yellow-orange and green regions of the visible spectrum. The bands in the green and red regions of GdVO4: Er3+/Nd3+ as well as GdVO4:Ho3+/Nd3+ were, respectively, characteristic of Er3+ and Ho3+ ions. The dominant band originating from the 4G7/2 → 4I11/2 transition in Nd3+ ions was observed around 597 nm in all samples.COST Action CM1403 (2014–2018); Ministry of Education, Science and Technological Development of the Republic of Serbia (Project Nos. 45020 and 172056 ); Latvian National Research Program IMIS2 (Grant No. 302/2012 ); ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 ( 1.1.1.2/16/I/001 ); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Particle size effects on the structure and emission of Eu3+:LaPO4 and EuPO4 phosphors

The authors acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Projects nos. 45020 and 172056). T.G acknowledges to the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 (1.1.1.2/16/I/001).This paper provides the detailed study of (nano)particle's size effect on structural and luminescent properties of LaPO4:Eu3+ synthesized by four different methods: high temperature solid-state, co-precipitation, reverse micelle and colloidal. These methods delivered monoclinic monazite-phase submicron particles (> 100 nm), 4 × 20 nm nanorods and 5 nm spheres (depending on the annealing temperature), 2 × 15 nm nanorods, and ultra-small spheres (2 nm), respectively. The analysis of emission intensity dependence on Eu3+ concentration showed that quenching concentration increases with a decrease of the particle size. The critical distance for energy transfer between Eu3+ ions is found to be 18.2 Å, and the dipole-dipole interaction is the dominant mechanism responsible for the concentration quenching of emission. With the increase in Eu3+ concentration, the unit-cell parameter slightly increases to accommodate larger Eu3+ ions at sites of smaller La3+ ions. Photoluminescent emission spectra presented four characteristic bands in the red spectral region: at 592 nm (5D0→7F1), at 612 nm (5D0→7F2), at 652 nm (5D0→7F3) and at 684 nm (5D0→7F4), while in small colloidal nanoparticles additional emission bands from host defects appear at shorter wavelengths. Intensities of f-f electronic transitions change with particles size due to small changes in symmetry around europium sites, while emission bandwidths increase with the reduction of particle size due to increased structural disorder. Judd-Ofelt analysis showed that internal quantum yield of Eu3+ emission is strongly influenced by particle's morphology.Ministry of Education, Science and Technological Development of the Republic of Serbia (Projects nos. 45020 and 172056); ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 (1.1.1.2/16/I/001); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

A comparative study of photocatalytically active nanocrystalline tetragonal T zyrcon- type and monoclinic scheelite-type bismuth vanadate

The authors from Vinča Institute of Nuclear Sciences acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Project no: 172056 ). The work of K. Smits was supported by Latvian National Research Program IMIS2 (Grant no. 302/2012 ).Monoclinic scheelite-type BiVO4 is currently considered as one of the most promising non-titania photocatalysts, wheras tetragonal zircon-type BiVO4 is still poorly understood. Herein, a new and simple synthetic approach was applied and nanostructured single-phase zircon-type BiVO4 was successfully prepared by a controllable ethylene-glycol colloidal route. In addition, nanostructured monoclinic scheelite-type BiVO4 powders were also fabricated through annealing of the as-prepared samples. A comparative study of the two BiVO4 polymorphs was conducted and it turned out that the novel synthetic approach had a significant impact on porosity and photocatalytic performance of zircon-structured BiVO4. All the prepared materials, as-prepared and annealed, were mesoporous, while measured values of specific surface area of some zircon-structured samples (∼34 m2/g) were ∼7 times higher than those reported thus far for this phase. Interestingly, for the first time, zircon-type BiVO4, previously considered to be a poor photocatalyst, exhibited a better overall performance in degradation of methyl orange compared to monoclinic scheelite-type BiVO4. Hence, it could be expected that the here-presented synthesis and observations will both arouse interest in scarcely studied tetragonal zircon-type BiVO4 and facilitate as well as speed up further research of its properties.Ministry of Education, Science and Technological Development of the Republic of Serbia (Project no: 172056 ); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Twofold increase in the sensitivity of Er3+/Yb3+ Boltzmann thermometer

Luminescence thermometry is the most versatile remote temperature sensing technique and can be employed from living cells to large surfaces and from cryogenic temperatures to the melting points of metals. Ongoing research aims to optimize the sensitivity of the ratio between the emission intensity from two coupled excited states. However, this approach is inherently limited to temperature-dependent processes involving only the excited states. Here, we develop a novel measurement technique, called luminescence intensity ratio squared (LIR2) for the Yb3+/Er3+ pair, that combines the temperature sensitivity of ground- and excited-state populations. We use Y3Al5O12:Er3+,Yb3+ nanoparticles as a promising model system with both visible and infrared emissions. To apply our method, we record two luminescence spectra at different excitation wavelengths and determine the LIR2 using one emission in each of the two spectra. The LIR2 testing with Y3Al5O12 nanoparticles showed a sensitivity increase of 70% in the visible region and an impressive 230% increase in the NIR region compared to the conventional LIR method. This enhances the measurement precision by a factor of 1.5-2.5. The LIR2 based on the visible upconversion emission is particularly useful for measurements of high temperatures, while the LIR2 based on the downshifted ∼1.5 μm emission may revolutionize temperature measurements of biological samples in the range of physiological temperatures

Influence of Er3+/Yb3+ Concentration Ratio on the Down-conversion and Up-conversion Luminescence and Lifetime in GdVO4:Er3+/Yb3+ Microcrystals

In this paper, we studied the effects of Er3+/Yb3+ concentration ratio on structural, morphological and luminescence properties of GdVO4:Er3+/Yb3+ green phosphors prepared by a high-temperature solid state method. The samples with different concentrations (between 0.5 to 2 mol%) of dopant Er3+ emitting ions and different concentrations (between 5 to 20 mol%) of sensitizer ions (Yb3+) were studied. The phosphors were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy. For all samples, XRD diffraction patterns confirmed a formation of a pure GdVO4 phase, while the SEM showed that the materials are comprised of chunks of deformed particles with an average diameter ranging from approximately 2 mu m to 8 mu m. Both, down-conversion and up-conversion emission spectra of GdVO4: Er3+/Yb3+ samples, under near UV and IR excitations, exhibit two strong emission bands in the green spectral region at 525 nm and 552 nm wavelengths corresponding to H-2(11/2) - gt I-4(15/2) and S-4(3/2) - gt I-4(15/2) electronic transitions of Er3+ ions. The intensity of the green emission was changed by changing the Er3+/Yb3+ concentration ratio. This dual-mode luminescence makes these materials ideal as green phosphors for a wide variety of applications in the fields of bioanalysis and biomedical

High-throughput first-principles calculations as a powerful guiding tool for materials engineering: Case study of the AB2X4 (A = Be, Mg, Ca, Sr, ba; B = Al, Ga, in; X = O, S) spinel compounds

Modern methods of theoretical and experimental materials engineering can be greatly facilitated by reliably established guiding trends that set directions for a smart search for new materials with enhanced performance. Those trends can be derived from a thorough analysis of large arrays of the experimental data, obtained both experimentally and theoretically. In the present paper, the structural, elastic, and electronic properties of 30 spinel compounds AB 2 X 4 (A = Be, Mg, Ca, Sr, Ba; B = Al, Ga, In; X = O, S) were investigated using the CRYSTAL14 program. For the first time the lattice constants, bulk moduli, band gaps and density of states for these 30 spinels were systematically calculated and analyzed. Influence of the cation and anion variation on the above-mentioned properties was highlighted. Several relations between lattice constants, bulk modulus and ionic radii, electronegativities of constituting ions were found. Several linear equations are proposed, which provide a convenient way to predict the lattice constants and bulk moduli of isostructural spinels. © 201

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

Supplementary data for article: Savić, T. D.; Šaponjić, Z. V.; Čomor, M. I.; Nedeljkovic, J. M.; Dramicanin, M. D.; Nikolić, M. G.; Veljković, D. Ž.; Zarić, S.; Janković, I. A. Surface Modification of Anatase Nanoparticles with Fused Ring Salicylate-Type Ligands (3-Hydroxy-2-Naphthoic Acids): A Combined DFT and Experimental Study of Optical Properties. Nanoscale 2013, 5 (16), 7601–7612. https://doi.org/10.1039/c3nr01277h

Supplementary material for: [https://doi.org/10.1039/c3nr01277h]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/1590