Anatase-to-rutile phase transition of samarium-doped TiO2 powder detected via the luminescence of Sm3+

AbstractWe employed a sol-gel route to prepare 1% samarium-doped TiO2 nanopowders. Time-resolved photoluminescence (PL) and Raman characterization was performed. After a thermal treatment the powder crystallized in an anatase phase and revealed intense Sm3+ photoluminescence. The emission spectrum of Sm3+ exposed well-resolved crystal-field splitting enabling monitoring of the changes in the local environment.We thoroughly investigated the influence of the annealing treatment (in air) on Sm emission intensity. Annealing up to 800 ∘C led to a systematic enhancement of Sm emission. Annealing at higher temperatures, however, led to a marked weakening of Sm3+ emission and simultaneous appearance of an emission band near 830 nm. Annealing temperatures as high as 1000 ∘C were needed to induce the phase transition from anatase to rutile. It was possible to use Sm3+ as a structural probe revealinge peculiarities of the phase transition

Phase stability and oxygen-sensitive photoluminescence of ZrO2:Eu,Nb nanopowders

This work was supported by institutional research funding ( IUT34-27 and IUT2-14 ) of the Estonian Ministry of Education and Research .We studied structure and oxygen-sensitive photoluminescence (PL) of ZrO2:Eu,Nb nanocrystalline powders synthesized via a sol-gel route and heat-treated up to 1200 °C. The material containing only 2 at% Eu3+ was predominantly monoclinic, whereas 8 at% of Eu3+ stabilized tetragonal phase. Comparable amount of niobium co-doping effectively suppressed the formation of tetragonal phase. PL of Eu3+ ions was observed under direct excitation at 395 nm. PL decay kinetics showed that the luminescence was partially quenched, depending on doping concentrations and ambient atmosphere. At 300 °C, the PL intensity of all samples systematically responded (with up to 70% change) to changing oxygen content in the O2/N2 mixture at atmospheric pressure. At low doping levels, the dominant factor controlling the PL intensity was an energy transfer from excited PL centers to randomly distributed defects in the ZrO2 lattice. We argue that the charge transfer between the defects and adsorbed oxygen molecules alters the ability of the defects to quench Eu3+ luminescence. At high doping levels, another type of sensor response was observed, where some Eu3+ emitters are effectively switched on or off by the change of ambient gas. A remarkable feature of the studied material is a reversing of the sensor response with the variation of the Nb concentration.Estonian Ministry of Education and Research IUT34-27 and IUT2-14; 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

Synthesis and vibration spectroscopy of nano-sized manganese oxides

The present study has been supported by the Latvian National Research Program IMIS2. One of us, IS, was supported by MES RF RFMEFI61615X0064.X-ray diffraction, micro-Raman and the Fourier transform infrared spectroscopies as well as magnetometry measurements were performed on nanosized manganese oxides to probe their phase composition and magnetic properties. It was shown that the XRD method is less sensitive to phase composition of manganese oxide samples than spectroscopic methods. While in some samples the XRD method recognised only the manganosite MnO phase, the Raman and FT-IR methods revealed additionally the presence of the hausmannite Mn3O4 phase.Ministry of Education and Science RF RFMEFI61615X0064; 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

Synthesis and vibration spectroscopy of nano-sized manganese oxides

The present study has been supported by the Latvian National Research Program IMIS2. One of us, IS, was supported by MES RF RFMEFI61615X0064.X-ray diffraction, micro-Raman and the Fourier transform infrared spectroscopies as well as magnetometry measurements were performed on nanosized manganese oxides to probe their phase composition and magnetic properties. It was shown that the XRD method is less sensitive to phase composition of manganese oxide samples than spectroscopic methods. While in some samples the XRD method recognised only the manganosite MnO phase, the Raman and FT-IR methods revealed additionally the presence of the hausmannite Mn3O4 phase.Ministry of Education and Science RF RFMEFI61615X0064; 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