A. Sarakovskis

The role of Nb in intensity increase of Er ion upconversion luminescence in zirconia

It is found that Nb co-doping increases the luminescence and upconversion luminescence intensity in rare earth doped zirconia. Er and Yb-doped nanocrystalline samples with or without Nb co-doping were prepared by sol-gel method and thermally annealed to check for the impact of phase transition on luminescence properties. Phase composition and grain sizes were examined by X-ray diffraction; the morphology was checked by scanning- and high-resolution transmission electron microscopes. Both steady-state and time-resolved luminescence were studied. Comparison of samples with different oxygen vacancy concentrations and different Nb concentrations confirmed the known assumption that oxygen vacancies are the main agents for tetragonal or cubic phase stabilization. The oxygen vacancies quench the upconversion luminescence; however, they also prevent agglomeration of rare-earth ions and/or displacement of rare-earth ions to grain surfaces. It is found that co-doping with Nb ions significantly (>20 times) increases upconversion luminescence intensity. Hence, ZrO2:Er:Yb:Nb nanocrystals may show promise for upconversion applications.

Multicolor Up-Conversion Luminescence in Rare-Earth Doped NaLaF4

In this work we tried to achieve multicolor up-conversion luminescence in low phonon energy material NaLaF4 doped with different Er3+ Tm3+ and Yb3+ concentrations. Up-conversion luminescence was measured and main luminescence bands from Er3+ and Tm3+ in red, green and blue spectral regions were observed. The relative intensities of the luminescence bands could be changed by changing the doping levels of rare-earth ions. Changes in the up-conversion luminescence color could be achieved by applying different infrared pump power density. The color coordinates of the multicolor up-conversion luminescence depending on doping level as well as on the pump power density were presented in CIE (x, y) chromaticity diagram (1931).

Synthesis of cubic and hexagonal NaYF4:Er3+

Up-conversion luminescence process, which is related to absorption of several light photons (usually infrared) followed by emission of light in the visible or even ultraviolet spectral regions, has attracted interest of scientists due to its potential practical use in various applications including biolabels, temperature sensors, light sources etc. Although observable in d- and f-ions doped materials, the highest efficiency of up-conversion luminescence is usually attained in lanthanides doped hosts. Among huge variety of materials suitable as up-conversion hosts the most prominent is considered to be NaYF4, both due to its low phonon energy and multisite nature of the crystalline lattice. In the present report erbium doped NaYF4 nanomaterial has been synthesized by a novel molten salt method. Depending on the synthesis temperature the structure of the material varied from solely cubic to exclusively hexagonal. It was found that the intensity of the up-conversion luminescence increased drastically as the structure of NaYF4:Er3+ changed from cubic to hexagonal.

Local structure studies of SrTi16O3 and SrTi18O3

In this work we report on the local structure of Ti in SrTi 16 O3 (STO16) and SrTi 18 O3 (STO18) investigated in the low temperature range (6‐300K) by extended x-ray absorption fine structure and x-ray absorption near edge structure (XANES) spectroscopy at Ti K-edge and by optical second harmonic generation (SHG). By comparing XANES of STO16 and STO18 we have identified the isotopic effect which produces at T < 100K a noticeable difference in the measured mean square relative displacements (MSRD) of Ti‐O1 bonds: while STO16 follow the expected Einstein-like behavior, for STO18 we have measured an increase of MSRD values with decreasing temperature. This is an indication of an increasing off-center position of the Ti atoms in the TiO6 octahedra.

Impact of Er3+ Concentration on Luminescence in NaLaF4

Abstract In this work, NaLaF4 doped with Er3+ of different concentrations was synthesized. The luminescence spectrum for NaLaF4:Er3+ (0.2 mol%) at 489 nm excitation reveals characteristic Er3+ luminescence bands in the green (540 nm), red (660 nm) and infrared (980 nm) spectral regions. The green luminescence band originated from the 4S3/2 → 4I15/2 transition is the most intensive one in the luminescence spectrum. As the concentration of the activator is increasing, the intensity of all luminescence bands changes significantly. The super-linear increase of the infrared luminescence intensity with increasing Er3+ concentration as well as the quenching of green luminescence at the concentrations exceeding 2 mol% can be attributed to the cross-relaxation process between the activator ions. Kopsavilkums Darbā pētīta Er3+ fotoluminiscences atkarība no Er3+ koncentrācijas NaLaF4 matricā. Pieaugot Er3+ koncentrācijai līdz 2mol% luminiscences intensitātes raksturīgajām Er3+ joslām zaļā (540nm), sarkanā (660nm) un infrasarkanajā (980 nm) spektra apgabalā pieaug. Pie Er3+ koncentrācijas virs 2mol% novērojama izteikta zaļās luminiscences koncentrācijas dzēšana un virslineārs infrasarkanās luminiscences joslas pieaugums, kas saistīts ar kross-relaksācijas procesiem starp aktivatora joniem.

Laser ablation for analysis of nanoscale layers

Deposition of carbon layer, tungsten and carbon migration, as well as retention, co-deposition and diffusion of hydrogen isotopes are the major concerns in fusion devices. We propose laser ablation spectroscopy as an effective method of rapid qualitative and quantitative surface mapping. An average growth of the deposited carbon layer in divertor region of a tokamak is about 0.2 nm/s. Depending on the number of discharges, the thickness of a layer can reach 200–400 nm. The information about the layer must be gained within this range of thickness. Obtained results show that proposed method can be used for analysis of layers in the range of thickness of several hundreds of nanometres.

Near-Infrared-to-Blue Up-conversion Luminescence in Transparent Eu3+/Yb3+ Doped Oxyfluoride Phosphors

In this paper transparent glass ceramics co-doped with Eu and Yb ions has been synthesized by melt quenching and subsequent heat treatment of the precursor glass. X-ray diffraction and transmission electron microscopy studies show precipitation of distorted PbF2 crystallites in the glass ceramics. Excitation at 976 nm leads to the appearance of UCL (up-conversion luminescence) with the strong bands characteristic to Eu ions. Luminescence studies suggest that Eu emission appears as the result of cooperative excitation of Yb ions and subsequent energy transfer to europium ions. The presence of Er and Tm impurities, identified in the course of the experiment, leads to the white up-conversion emission of phosphors under the study.

12th Russia/CIS/Baltic/Japan Symposium on Ferroelectricity and 9th International Conference on Functional Materials and Nanotechnologies (RCBJSF?2014?FM&NT)

The joint International Symposium RCBJSF–2014–FM&NT successfully has united two international events – 12th Russia/CIS/Baltic/Japan Symposium on Ferroelectricity (RCBJSF-12) and 9th International Conference Functional Materials and Nanotechnologies (FM&NT-2014). The RCBJSF symposium is a continuation of series of meetings on ferroelectricity, the first of which took place in Novosibirsk (USSR) in 1976. FM&NT conferences started in 2006 and have been organized by Institute of Solid State Physics, University of Latvia in Riga. In 2012 the International program committee decided to transform this conference into a traveling Baltic State conference and the FM&NT-2013 was organized by the Institute of Physics, University of Tartu, Estonia. In 2014 the joint international symposium RCBJSF–2014–FM&NT was organized by the Institute of Solid State Physics, University of Latvia and was part of Riga – 2014, the European Capital of Culture event. The purpose of the joint Symposium was to bring together scientists, students and high-level experts in solid state physics, materials science, engineering and related disciplines. The number of the registered participants from 26 countries was over 350. During the Symposium 128 high quality scientific talks (5 plenary, 42 invited, 81 oral) and over 215 posters were presented. All presentations were divided into 4 parallel sessions according to 4 main topics of the Symposium: Ferroelectricity, including ferroelectrics and multiferroics, pyroelectrics, piezoelectrics and actuators, integrated ferroelectrics, relaxors, phase transitions and critical phenomena. Multifunctional Materials, including theory, multiscale and multiphenomenal material modeling and simulation, advanced inorganic, organic and hybrid materials. Nanotechnologies, including progressive methods, technologies and design for production, investigation of nano- particles, composites, structures, thin films and coatings. Energy, including perspective materials and technologies for renewable and hydrogen energy, fuel cells, photovoltaics, LEDs, OLEDs. Based on these reports, 48 papers are included in this volume of IOP Conference Series: Materials Science and Engineering. Additional information about RCBJSF–2014–FM&NT is available at the homepage http://www.fmnt.lu.lv. The Organizing Committee would like to thank all the speakers, contributors, session chairs, referees and other involved staff for their efforts in making the RCBJSF–2014–FM&NT successful. Sincerely, organizers of the event Andris Sternberg Liga Grinberga Anatolijs Sarakovskis Martins Rutkis

Local Structure Studies of Ti for SrTi16O3 and SrTi18O3 by Advanced X-ray Absorption Spectroscopy Data Analysis

Strontium titanate is a model quantum paraelectric in which in the region of dominating quantum statistics the ferroelectric instability is inhibited due to nearly complete compensation of the harmonic contribution into ferroelectric soft mode frequency by the zero-point motion contribution. The enhancement of atomic masses by the substitution of 18O for 16O decreases the zero-point atomic motion and low-T ferroelectricity in SrTi18O3 is realized. In this study we report on the local structure of Ti in SrTi16O3 and SrTi18O3 by Ti K-edge extended x-ray absorption fine structure measurements in temperature range 6 – 300 K.

Dynamics of exciton creation and decay processes in composition – disordered InGaN thin films

In the GaN-based ternary alloys, InGaN crystals have been recognized as key materials for e-h plasmas-exciton dynamics, because of large exciton binding energies (24.8 meV in GaN). We report investigations of creating and recombination dynamics of excitons in commercially important InxGa1-xN composition range from x = 0.1 to 0.18 in which nanoscale indium composition fluctuation occurs and formation of indium rich clusters acting as quantum dots (QD) can be expected. Three MOCVD grown samples having x = 0.1; 0.14 and 0.18 have been investigated using 3D picosecond transient PL spectroscopy. It has been found that the band to band photo excitation at 15 K in whole composition range results in creating of complex luminescence band represented by three close overlapping Gaussian shape single exciton bands. All three exciton bands show fast decay time constants in a picosecond range. For all the samples the PL intensity dependence on excitation pulse power for each exciton band is different. An increase of the excitation pulse power density results in the linear growth of the band at the higher photon energy side. The next energy bands with lower photon energy show correspondingly quadratic and cubic dependences on laser pulse energy and are caused by the formation of biexcitons and triexcitons. Fast decay kinetics and excitation of multi-excitonic complexes are evident for important role of quantum dots by quantum capture of excitons in the considered composition range.