EPR studies of manganese centers in SrTiO3: Non-Kramers Mn3+ ions and spin-spin coupled Mn4+ dimers

X- and Q-band electron paramagnetic resonance (EPR) study is reported on the SrTiO3 single crystals doped with 0.5-at.% MnO. EPR spectra originating from the S = 2 ground state of Mn3+ ions are shown to belong to the three distinct types of Jahn-Teller centres. The ordering of the oxygen vacancies due to the reduction treatment of the samples and consequent formation of oxygen vacancy associated Mn3+ centres are explained in terms of the localized charge compensation. The EPR spectra of SrTiO3: Mn crystals show the presence of next nearest neighbor exchange coupled Mn4+ pairs in the directions.Comment: 17 pages, 8 figure

The spin relaxation of nitrogen donors in 6H SiC crystals as studied by the electron spin echo method

We present the detailed study of the spin kinetics of the nitrogen (N) donor electrons in 6H SiC wafers grown by the Lely method and by the sublimation “sandwich method” (SSM) with a donor concentration of about 10 17cm-3 at T=10–40K. The donor electrons of the N donors substituting quasi-cubic “k1” and “k2” sites (Nk1,k2) in both types of the samples revealed the similar temperature dependence of the spin-lattice relaxation rate (T1 -1), which was described by the direct one-phonon and two-phonon processes induced by the acoustic phonons proportional to T and to T9, respectively. The character of the temperature dependence of the T1 -1 for the donor electrons of N substituting hexagonal (“h”) site (Nh) in both types of 6H SiC samples indicates that the donor electrons relax through the fast-relaxing centers by means of the cross-relaxation process. The observed enhancement of the phase memory relaxation rate (Tm -1) with the temperature increase for the Nh donors in both types of the samples, as well as for the Nk1,k2 donors in Lely grown 6H SiC, was explained by the growth of the free electron concentration with the temperature increase and their exchange scattering at the N donor centers. The observed significant shortening of the phase memory relaxation time Tm for the Nk1,k2 donors in the SSM grown sample with the temperature lowering is caused by hopping motion of the electrons between the occupied and unoccupied states of the N donors at Nh and Nk1,k2 sites. The impact of the N donor pairs, triads, distant donor pairs formed in n-type 6H SiC wafers on the spin relaxation times was discussed

Chiral plasmonic response of 2D Ti3C2Tx flakes: realization and applications

The circularly polarized light sensitive materials response can be reached at plasmon wavelengths through the coupling of intrinsically non-chiral plasmonic nanostructure with chiral organic molecules. As a plasmonic background, the different types of metal nanoparticles of various shapes and sizes are successfully tested and an apparent circular dichroism (CD) signal is measured in both, nanoparticles suspensions and after nanoparticle immobilization in substrate. In this work, the creation of plasmon-active 2D flakes of MXenes (Ti3C2Tx) is proposed, with the apparent CD response at plasmon wavelength, through the coupling of intrinsically non-chiral flakes with helically shaped helicene enantiomers. This work provides the first demonstration of chiral and plasmon-active 2D material, which shows the absorption sensitive to light intrinsic circular polarization even in plasmon wavelengths range. The appearance of the induced CD signal is additionally confirmed by several theoretical calculations. After the experimental and theoretical confirmation of the optical chirality at plasmon wavelengths, the flakes are utilized for the polarization sensitive conversion of light to heat, as well as for polarization dependent triggering of plasmon-assisted chemical transformation

Optical, structural and fluorescence properties of nanocrystalline cubic or monoclinic Eu:Lu2O3 films prepared by pulsed laser deposition

International audienceEu3+-doped lutetium oxide (Eu:Lu2O3) nanocrystalline films were grown on fused-silica substrates by pulsed laser deposition. Depending on deposition conditions (oxygen pressure, temperature and laser energy), the structure of the films changed from amorphous to crystalline and the cubic or monoclinic phases were obtained with varying preferential orientation and crystallite size. The monoclinic phase could be prepared for the first time at temperatures as low as 240 °C and in a narrow range of parameters. Although this phase has been previously reported for powder samples, it occurs only for high pressures and high temperatures preparation conditions. The refractive indices were measured by m-lines spectroscopy for both crystalline phases and their dispersion curve fitted by the Sellmeier expression. The specific Eu3+ fluorescence properties of the different phases, monoclinic and cubic, were registered and show modifications due to the disorder induced by the nanometric size of the crystallites, emphasised in particular by quasi-selective excitation in the charge transfer band

Diffractive and coloured films by laser interferometry patterning

Coloured coatings having both selective optical and diffractive properties have been produced by phase-mask laser interference with a UV laser beam (193 nm and 20 ns pulse duration). The method has been demonstrated on Ag films prepared by magnetron sputtering having equivalent thickness ranging from nearly isolated nanoparticles to continuous film. The laser induces periodic patterns formed by non-transformed film areas surrounded by areas containing nanoparticles whose dimensions are controlled through the as-grown film thickness. The nanoparticles are found responsible for a reflectivity band peaking in the range 446¿545 nm depending on the thickness and associated to their surface plasmon resonance that provides the ¿colour¿. The morphology of the pattern can be controlled through the laser energy, number of pulses and the phase-mask configuration and has a unique diffraction pattern associated. This approach allows producing customised coloured coatings with an identification feature. Although the concept is shown for a silver film and rectangular patterns, it can easily be extended to many other types of materials or patterns.This work has partially been supported by the joint 2008CZ0018 project between CSIC (Spain) and ASCR (Czech Republic). RP acknowledges a grant from the JAE-doc programme. MN's research was supported by project GACR GP202/09/P324. JB's research was supported by Grant Agency of Czech Academy of Sciences, project IAA100100718.Peer Reviewe

Influence of the PLD parameters on the crystalline phases and fluorescence of Eu:Y2O3 planar waveguides

International audienceEu3+-doped yttrium oxide (Eu:Y2O3) films were grown on fused-silica substrates by laser ablation. Depending on oxygen pressure, substrate temperature and laser energy density, the crystalline structure of the films, determined by X-ray diffraction and Raman spectroscopy, changes from monoclinic to cubic. The crystalline structure of the films is confirmed by Eu3+ fluorescence spectra and refractive indices, measured by m-line spectroscopy. The cubic crystalline films show low-loss waveguiding properties

Difractive and coloured films patterned by laser interferometry

Trabajo presentado en el E-MRS ICAM IUMRS 2011 Spring Meeting (Symposium K : Protective coatings and thin films), celebrado en Niza (Francia), del 9 al 13 de mayo de 201

The spin relaxation of nitrogen donors in 6H SiC crystals as studied by the electron spin echo method

We present the detailed study of the spin kinetics of the nitrogen (N) donor electrons in 6H SiC wafers grown by the Lely method and by the sublimation “sandwich method” (SSM) with a donor concentration of about 10 17cm-3 at T=10–40K. The donor electrons of the N donors substituting quasi-cubic “k1” and “k2” sites (Nk1,k2) in both types of the samples revealed the similar temperature dependence of the spin-lattice relaxation rate (T1 -1), which was described by the direct one-phonon and two-phonon processes induced by the acoustic phonons proportional to T and to T9, respectively. The character of the temperature dependence of the T1 -1 for the donor electrons of N substituting hexagonal (“h”) site (Nh) in both types of 6H SiC samples indicates that the donor electrons relax through the fast-relaxing centers by means of the cross-relaxation process. The observed enhancement of the phase memory relaxation rate (Tm -1) with the temperature increase for the Nh donors in both types of the samples, as well as for the Nk1,k2 donors in Lely grown 6H SiC, was explained by the growth of the free electron concentration with the temperature increase and their exchange scattering at the N donor centers. The observed significant shortening of the phase memory relaxation time Tm for the Nk1,k2 donors in the SSM grown sample with the temperature lowering is caused by hopping motion of the electrons between the occupied and unoccupied states of the N donors at Nh and Nk1,k2 sites. The impact of the N donor pairs, triads, distant donor pairs formed in n-type 6H SiC wafers on the spin relaxation times was discussed