Ilmo Sildos - Academia.edu (original) (raw)

Papers by Ilmo Sildos

physica status solidi (a), 2020

Herein optical properties of aggregates of hydrophobic nanodiamonds (NDs) with germanium‐vacancy ... more Herein optical properties of aggregates of hydrophobic nanodiamonds (NDs) with germanium‐vacancy (GeV) defects distributed on substrates with different hydrophilicities (bare Si or TiO2 (anatase) film on Si substrate) are investigated with an aim to achieve millimeter‐scale, nearly homogeneous spatial distribution of ND aggregates. ND aggregates are spread by drop casting of a water colloid. The luminescence spectra of GeV defects are studied in a wide temperature range (85–400 K). The possibility of optical thermometry operating in a wide temperature range also covering biotemperatures is demonstrated using a separate microaggregate of NDs on the anatase film.

In this study we have performed investigation of stoichiometric and non-stoichiometric manganese ... more In this study we have performed investigation of stoichiometric and non-stoichiometric manganese oxides (polycrystalline and single-crystal) using x-ray diffraction (XRD), microRaman and FT-IR spectroscopy. Polycrystalline MnO and Mn3O4 were prepared by thermal decomposition of oxalate or manganese carbonate in vacuum and in air, respectively. Single-crystals MnO and Mn3O4 (hausmannite) were grown by the method of chemical transport reactions from polycrystalline sources on MgO(100) substrate. All samples were characterized by x-ray diffraction. It is known that MnO phase with a NaCl-type structure is a weak Raman scatterer. Its Raman signal consists of two broad asymmetric bands at about 530 cm and 1050 cm, of which only the first one has been attributed to 2TO mode. The Raman spectrum of polycrystalline tetragonal hausmannite Mn3O4 consists of a narrow strong band at 660 cm and two small bands at about 318 and 370 cm. The contribution from hausmannite phase is well visible in mixe...

IOP Conference Series: Materials Science and Engineering, 2015

Nanocrystalline NiO has been produced using a facile template-based synthesis from nickel nitrate... more Nanocrystalline NiO has been produced using a facile template-based synthesis from nickel nitrate solutions using cellulose as a template. Thus obtained oxides were studied by scanning electron microscopy, x-ray diffraction, Raman scattering spectroscopy, photoluminescence spectroscopy and confocal spectromicroscopy. The filamentary/coral morphology of the samples has been evidenced and is built up of agglomerated nanocrystallites with a size in the range of about 26-36 nm. The presence of two-magnon contribution in Raman scattering spectra suggests the existence of antiferromagnetic ordering at room temperature. Finally, the observed near-infrared photoluminescence band at 850 nm has been tentatively attributed to the defect-perturbed Ni 2+ states at the surface.

Plasma Medicine, 2016

In this study we investigated the interaction of atmospheric-pressure helium (He) and He/ H 2 pul... more In this study we investigated the interaction of atmospheric-pressure helium (He) and He/ H 2 pulsed-discharge plasma with different water solutions. We developed a synthetic path to obtain fairly uniform, small (~2 nm), surfactant-free silver (Ag) nanoparticles (NPs) with the treatment of an AgNO 3 solution with He/H 2 bipolar pulsed discharge. The colloidal solutions containing Ag NPs are stable for months negatively charged hydroxide (OH) ions on the surface of Ag NPs could be responsible for the electrostatic stabilization. The treatment of the air-saturated water by pure He plasma with a negative polarity leads to the creation of HNO 3 and hydrogen peroxide (H 2 O 2 solution by He plasma treatment, He/H 2 discharge with negative and, in particular, with bipolar pulses produces only traces of HNO 3 and no H 2 O 2. We demonstrate here that He/H 2 discharge with bipolar pulses 3 and KNO 3 solutions.

Diamond and Related Materials, 2017

We carried out a laser spectroscopic investigation of high-pressure, high-temperature (HTHP) synt... more We carried out a laser spectroscopic investigation of high-pressure, high-temperature (HTHP) synthetic diamond containing NE8 defects. In the photoluminescence (PL) emission spectra the defects have a zero-phonon line (ZPL) at 794 nm. Under 730 nm excitation the width and position of the ZPL as well as the Debye-Waller factor showed systematic temperature dependences which were modelled in accordance of a modified model of impurity defects in solids. A strong dependence of the position of the 794 nm ZPL on temperature suggests that NE8-containing diamond could be suitable for sensitive optical thermometry above 200 K. Further, the PL in the NIR spectral range makes the diamond crystalline particles promising temperature sensors for biomedical applications.

Journal of Luminescence, 2013

The electronic energy levels of six-fold coordinated Ni 2 þ ion in magnesium oxide MgO were calcu... more The electronic energy levels of six-fold coordinated Ni 2 þ ion in magnesium oxide MgO were calculated using the exchange charge model of crystal field theory. The calculated energetic positions of the Ni 2 þ levels match well the experimental spectrum. Inclusion of the spin-orbit (SO) interaction is compulsory to account for the first excited 3 T 2g state fine structure; however, it does not explain why out of four levels arising from the 3 T 2g state, only two are seen in the experimental spectra. One possible explanation to this fact can be advanced by invoking the Jahn-Teller effect.

The Journal of Chemical Physics, 2003

We are studying the optical spectra of impurity centers in the case when the optical transition t... more We are studying the optical spectra of impurity centers in the case when the optical transition takes place between nondegenerate and two-fold degenerate electronic E-states characterized by a strong vibronic coupling. In the latter state the adiabatic surface has a shape of a deformed Mexican hat with three flat minima on the trough of the “hat.” We have found that in this case the usual T7-dependence of the homogeneous width of the zero-phonon line at low temperatures is replaced by a dependence close to the T3-one. Besides, the usual T4-dependent redshift of the line is replaced by the T2-dependent shift. Depending on the flatness of the adiabatic surface, the latter shift may be to the red or to the blue. The theory is applied to the zero-phonon line 637 nm of the nitrogen-containing N-V center in a diamond. In this system the temperature dependence of the ZPL results from the common action of the Jahn–Teller effect and the pseudo-Jahn–Teller effect in the excited E-state: the p...

Ferroelectrics, 2001

ABSTRACT The one-magnon (1M) and two-magnon (2M) contributions were studied in optical absorption... more ABSTRACT The one-magnon (1M) and two-magnon (2M) contributions were studied in optical absorption spectra of KNiF3 single crystal, measured in the temperature range from 5 K to 300 K. The three absorption bands were considered in details. The first band is due to the magnetic-dipole transition A2g(F) → T2g(F), centred at 7700 cm, and contains the Brillouin zone-centre one-magnon contribution with the energy ω1M = 25 ± 5 cm. The other two bands are due to the electric-dipole transitions A2g(F) → Eg(D) and A2g(F) → Eg(G), centred at 16000 cm and 31200 cm, respectively. Both bands contain the Brillouin zone-boundary two-magnon contribution with the energy ω2M 813 ± 10 cm.

Chemical Physics Letters, 1985

ABSTRACT

Optical Materials, 2010

ABSTRACT In the frame of the current work novel set of Sm-doped zirconia (ZrO2) microrolls were c... more ABSTRACT In the frame of the current work novel set of Sm-doped zirconia (ZrO2) microrolls were composed by using specially modified sol–gel technique followed by annealing cycle from 500°C to 800°C. Via Raman and XRD scattering of zirconia as well as the photoluminescence (PL) spectra of the samarium ions the crystal phase formation was monitored and characterised qualitatively. The microrolls are shown first to form tetragonal phase which is stabilised by Sm ions, residual organic dopants and shear forces acting on the bent surface. The microrolls go through phase transformation to monoclinic as the annealing temperature is increased leading to partial breakup of the macroscopic structure.

Optical Materials, 2010

Composite based on TiO 2 host doped with Sm 3+ ions and co-doped with silver nanoparticles is pro... more Composite based on TiO 2 host doped with Sm 3+ ions and co-doped with silver nanoparticles is proposed as new fluorescent material. The co-doped samples were prepared from titanium alkoxide precursor by sol-gel method adjusted for addition of Sm 3+ ions and Ag nanoparticles. Commercial samarium nitrate salt and silver nanopowder (size of primary particle 30-50 nm) were used as dopant and co-dopant. Raman measurements revealed that crystalline anatase TiO 2 phase is typical for the TiO 2 :Sm 3+ films, whereas TiO 2 :Sm 3+ -Ag samples contain regions of rutile and brookite phases distributed in the predominantly amorphous TiO 2 surrounding. Samarium ions were excited either directly (k exc = 488 nm) or through the TiO 2 host (k exc = 355 nm). Enhancement of Sm 3+ fluorescence up to 20 times was revealed in the vicinity of silver aggregates. Combined plasmonic and sensitizing influences of silver on the Sm 3+ ions are considered as reasons for enhanced Sm 3+ fluorescence.

Optical Materials, 2004

Spectral and spatial properties of the excitonic luminescence of TiO 2 (anatase) waveguide layers... more Spectral and spatial properties of the excitonic luminescence of TiO 2 (anatase) waveguide layers grown by the atomic layer deposition on dielectric and metal substrates were investigated at low temperatures. Significant changes in self-trapped-excitonic (STE) spectra were observed in the direction nearly parallel to the film surface. The characteristic broad band STE emission spectrum of anatase peaking at $2.3 eV was transformed into directed spectrally narrow polarised bands. It was concluded that the leaky modes of the planar waveguide were responsible for this effect.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005

Emission, excitation and absorption spectra of HfO 2 and ZrO 2 thin films grown by atomic layer d... more Emission, excitation and absorption spectra of HfO 2 and ZrO 2 thin films grown by atomic layer deposition were investigated in the temperature range of 10-300 K. Time-resolved luminescence spectra were excited with a pulsed ArF laser and tuneable synchrotron radiation in UV-VUV. The strong emission with the peak position at 4.2-4.4 eV and with the decay time in ms range was revealed at 10 K in both materials. The emission was ascribed to the radiative decay of self-trapped excitons (STE). the features observed in the absorption and excitation spectra at 5.8 and 5.4 eV were most probably due to the formation of excitons; While the interband transitions started to dominate at 6.15 and 5.85 ev in HfO 2 and ZrO 2 , respectively.

Nature Nanotechnology, 2013

Doping of carbon nanoparticles with impurity atoms is central to their application 1,2 . However,... more Doping of carbon nanoparticles with impurity atoms is central to their application 1,2 . However, doping has proven elusive for very small carbon nanoparticles because of their limited availability and a lack of fundamental understanding of impurity stability in such nanostructures 3 . Here, we show that isolated diamond nanoparticles as small as 1.6 nm, comprising only ∼400 carbon atoms, are capable of housing stable photoluminescent colour centres, namely the silicon vacancy (SiV) 4,5 . Surprisingly, fluorescence from SiVs is stable over time, and few or only single colour centres are found per nanocrystal. We also observe size-dependent SiV emission supported by quantum-chemical simulation of SiV energy levels in small nanodiamonds. Our work opens the way to investigating the physics and chemistry of molecular-sized cubic carbon clusters and promises the application of ultrasmall non-perturbative fluorescent nanoparticles as markers in microscopy and sensing.

Nanoscale Research Letters, 2014

Silica-gold core-shell nanoparticles were used for plasmonic enhancement of rare earth fluorescen... more Silica-gold core-shell nanoparticles were used for plasmonic enhancement of rare earth fluorescence in sol-gel-derived TiO 2 :Sm 3+ films. Local enhancement of Sm 3+ fluorescence in the vicinity of separate gilded nanoparticles was revealed by a combination of dark field microscopy and fluorescence spectroscopy techniques. An intensity enhancement of Sm 3+ fluorescence varies from 2.5 to 10 times depending on the used direct (visible) or indirect (ultraviolet) excitations. Analysis of fluorescence lifetimes suggests that the locally stronger fluorescence occurs because of higher plasmon-coupled direct absorption of exciting light by the Sm 3+ ions or due to plasmon-assisted non-radiative energy transfer from the excitons of TiO 2 host to the rare earth ions.

Materials Science and Engineering: B, 2004

High-quality nanocrystalline TiO2 thin films of anatase phase were prepared by using the atomic l... more High-quality nanocrystalline TiO2 thin films of anatase phase were prepared by using the atomic layer deposition technique and implanted with Sm3+ ions. After the annealing of the films a band-to-band optical excitation of TiO2 at low temperatures led to a broadband excitonic emission superposed by a Sm3+-specific emission series of a well-pronounced fine structure. At higher temperatures (>250K) only the

Journal of Physics: Condensed Matter, 2011

This research is focused on the 4f-5d transitions in Ce 3+ centers doped into tetragonal β-SrAlF ... more This research is focused on the 4f-5d transitions in Ce 3+ centers doped into tetragonal β-SrAlF 5 single crystals belonging to the I 4 1 /a space group. The presence of four non-equivalent Sr 2+ sites in this compound leads to the appearance of three spectroscopically non-equivalent Ce 3+ luminescence centers, which can be well distinguished using a time-resolved laser spectroscopy technique. All 4f-5d transitions have slightly varying excitation and emission energies with characteristic probabilities resulting in several decay times that can be determined experimentally. One of these centers experiences strong perturbation due to a defect nearby, probably the O 2− impurity ion substituting for the F − ion and acting as a charge compensator as well. Identification of these photoluminescence centers is performed using crystal field calculations. The crystal field parameters are calculated for two identified centers using the structural data for SrAlF 5 ; diagonalization of the crystal field Hamiltonian results in obtaining the splitting of the Ce 3+ 5d states. This method allows 'regular' unperturbed Ce 3+ centers with selected Sr 2+ sites to be assigned.

Journal of Physics D: Applied Physics, 2009

ABSTRACT A systematic study of the photoluminescence spectra of samarium-doped crystalline TiO2 w... more ABSTRACT A systematic study of the photoluminescence spectra of samarium-doped crystalline TiO2 was conducted within the temperature range 10–300 K in order to reveal the energy levels of the trivalent impurity ion in different phases of titania. The sol–gel route was used to prepare Sm-doped TiO2 powders. The nanocrystalline anatase phase was obtained by annealing up to 800 °C, whereas the rutile phase was developed by annealing above 1000 °C. Crystal field calculations of Sm3+ energy levels in the two phases of TiO2 (anatase and rutile) were performed for the first time. The obtained set of energy levels assuming positioning of the Sm3+ ions in regular TiO2 lattice sites was consistent with the experimental results. The effect of the different phases of titania on the impurity is discussed.

Journal of Physics: Conference Series, 2007

Magnetic ordering in nanosized (100 and 1500 nm) nickel oxide NiO powders, prepared by the plasma... more Magnetic ordering in nanosized (100 and 1500 nm) nickel oxide NiO powders, prepared by the plasma synthesis method, was studied using Raman scattering spectroscopy in a wide range of temperatures from 10 to 300 K. It was observed that the intensity of twomagnon band decreases rapidly for smaller crystallites size. This effect is attributed to a decrease of antiferromagnetic spin correlations and leads to the antiferromagnetic-toparamagnetic phase transition .

Journal of Physics: Conference Series, 2010

Wide band-gap, high refractive index, good mechanical and high optical damage threshold are in pa... more Wide band-gap, high refractive index, good mechanical and high optical damage threshold are in particular the properties rendering zirconium oxide (ZrO 2 ) rather interesting material for various applications such as laser cavities, optical coatings, gas sensors or insulating layers in semiconductor devices. Low phonon energies (<400 cm -1 ) and wide band-gap (5.85 eV) simultaneously make ZrO 2 especially promising host for optically active dopants. Doping of ZrO 2 with various rare earth (RE) ions and creation of intrinsic defects in the pure crystal has been reported by several authors ]. In many cases, though, the nature of the excitation mechanisms leading to the emission of RE ions and intrinsic excitations is still a topic of ongoing debates ]. This is mainly because of the rather complicated electronic and phase structure caused by the dopants, ability to stabilize zirconia in tetragonal and cubic phases in addition to the only naturally stable monoclinic phase at RT. Stabilization of many of the dopants in the crystal lattice needs charge compensation, which can modify the density of states of ZrO 2 . In our work we aimed on identification of the various defect levels involved in energy-transfer processes in ZrO 2 and on revealing of different sites of optical centers by using combined excitation-emission spectroscopic studies (CEES).The investigated Sm doped bulk ZrO 2 sample was prepared by using the directional solidification of melt[ 7 ]. Phase content of the sample was determined via micro-Raman and XRD spectra. The photoluminescence (PL) measurements in the range from 3 eV to 20 eV cover both direct excitation energy range of the dopants as well as the intrinsic host absorption. Synchrotron radiation in VUV, a tuneable OPO laser and a xenon lamp were applied as excitation sources. Low temperature measurements were carried out to determine the activation energies of defect-related electronic processes. The results show that PL spectra of ZrO 2 :Sm 3+ are narrow-lined, which is typical for the f-f transitions of Sm ion in trivalent charge state. No intrinsic self-trapped exciton emission, found in high quality crystalline and thin crystalline zirconia films[ 5 ] nor various F-centre related broad band emissions, usually present in yttria-stabilized pure zirconia[ 6,8 ], were revealed in the samples even under band-to-band excitation. High dopant concentration (4 mol%), effective energy transfer to the Sm 3+ ions and rather defective structure of the mixed phase material causing appearance of efficient nonradiative decay channels are considered as main reasons of absence of intrinsic photoluminescence. Dopant-related PL was found to be many orders of magnitude more effective via band-to-band excitation of the host than through the direct intra-centre excitation of Sm 3+ ions . The presence of at least two different PL sites for the dopant ions were determined and characterized from temperature dependent CEES. Further studies using time-resolved PL spectra and decay measurements confirmed our hypotheses. Taking into account relatively good emission properties of the material, its application potential in various fields as light generation, scintillation, and gas sensing will be discussed.

physica status solidi (a), 2020

Herein optical properties of aggregates of hydrophobic nanodiamonds (NDs) with germanium‐vacancy ... more Herein optical properties of aggregates of hydrophobic nanodiamonds (NDs) with germanium‐vacancy (GeV) defects distributed on substrates with different hydrophilicities (bare Si or TiO2 (anatase) film on Si substrate) are investigated with an aim to achieve millimeter‐scale, nearly homogeneous spatial distribution of ND aggregates. ND aggregates are spread by drop casting of a water colloid. The luminescence spectra of GeV defects are studied in a wide temperature range (85–400 K). The possibility of optical thermometry operating in a wide temperature range also covering biotemperatures is demonstrated using a separate microaggregate of NDs on the anatase film.

In this study we have performed investigation of stoichiometric and non-stoichiometric manganese ... more In this study we have performed investigation of stoichiometric and non-stoichiometric manganese oxides (polycrystalline and single-crystal) using x-ray diffraction (XRD), microRaman and FT-IR spectroscopy. Polycrystalline MnO and Mn3O4 were prepared by thermal decomposition of oxalate or manganese carbonate in vacuum and in air, respectively. Single-crystals MnO and Mn3O4 (hausmannite) were grown by the method of chemical transport reactions from polycrystalline sources on MgO(100) substrate. All samples were characterized by x-ray diffraction. It is known that MnO phase with a NaCl-type structure is a weak Raman scatterer. Its Raman signal consists of two broad asymmetric bands at about 530 cm and 1050 cm, of which only the first one has been attributed to 2TO mode. The Raman spectrum of polycrystalline tetragonal hausmannite Mn3O4 consists of a narrow strong band at 660 cm and two small bands at about 318 and 370 cm. The contribution from hausmannite phase is well visible in mixe...

IOP Conference Series: Materials Science and Engineering, 2015

Nanocrystalline NiO has been produced using a facile template-based synthesis from nickel nitrate... more Nanocrystalline NiO has been produced using a facile template-based synthesis from nickel nitrate solutions using cellulose as a template. Thus obtained oxides were studied by scanning electron microscopy, x-ray diffraction, Raman scattering spectroscopy, photoluminescence spectroscopy and confocal spectromicroscopy. The filamentary/coral morphology of the samples has been evidenced and is built up of agglomerated nanocrystallites with a size in the range of about 26-36 nm. The presence of two-magnon contribution in Raman scattering spectra suggests the existence of antiferromagnetic ordering at room temperature. Finally, the observed near-infrared photoluminescence band at 850 nm has been tentatively attributed to the defect-perturbed Ni 2+ states at the surface.

Plasma Medicine, 2016

In this study we investigated the interaction of atmospheric-pressure helium (He) and He/ H 2 pul... more In this study we investigated the interaction of atmospheric-pressure helium (He) and He/ H 2 pulsed-discharge plasma with different water solutions. We developed a synthetic path to obtain fairly uniform, small (~2 nm), surfactant-free silver (Ag) nanoparticles (NPs) with the treatment of an AgNO 3 solution with He/H 2 bipolar pulsed discharge. The colloidal solutions containing Ag NPs are stable for months negatively charged hydroxide (OH) ions on the surface of Ag NPs could be responsible for the electrostatic stabilization. The treatment of the air-saturated water by pure He plasma with a negative polarity leads to the creation of HNO 3 and hydrogen peroxide (H 2 O 2 solution by He plasma treatment, He/H 2 discharge with negative and, in particular, with bipolar pulses produces only traces of HNO 3 and no H 2 O 2. We demonstrate here that He/H 2 discharge with bipolar pulses 3 and KNO 3 solutions.

Diamond and Related Materials, 2017

We carried out a laser spectroscopic investigation of high-pressure, high-temperature (HTHP) synt... more We carried out a laser spectroscopic investigation of high-pressure, high-temperature (HTHP) synthetic diamond containing NE8 defects. In the photoluminescence (PL) emission spectra the defects have a zero-phonon line (ZPL) at 794 nm. Under 730 nm excitation the width and position of the ZPL as well as the Debye-Waller factor showed systematic temperature dependences which were modelled in accordance of a modified model of impurity defects in solids. A strong dependence of the position of the 794 nm ZPL on temperature suggests that NE8-containing diamond could be suitable for sensitive optical thermometry above 200 K. Further, the PL in the NIR spectral range makes the diamond crystalline particles promising temperature sensors for biomedical applications.

Journal of Luminescence, 2013

The electronic energy levels of six-fold coordinated Ni 2 þ ion in magnesium oxide MgO were calcu... more The electronic energy levels of six-fold coordinated Ni 2 þ ion in magnesium oxide MgO were calculated using the exchange charge model of crystal field theory. The calculated energetic positions of the Ni 2 þ levels match well the experimental spectrum. Inclusion of the spin-orbit (SO) interaction is compulsory to account for the first excited 3 T 2g state fine structure; however, it does not explain why out of four levels arising from the 3 T 2g state, only two are seen in the experimental spectra. One possible explanation to this fact can be advanced by invoking the Jahn-Teller effect.

The Journal of Chemical Physics, 2003

We are studying the optical spectra of impurity centers in the case when the optical transition t... more We are studying the optical spectra of impurity centers in the case when the optical transition takes place between nondegenerate and two-fold degenerate electronic E-states characterized by a strong vibronic coupling. In the latter state the adiabatic surface has a shape of a deformed Mexican hat with three flat minima on the trough of the “hat.” We have found that in this case the usual T7-dependence of the homogeneous width of the zero-phonon line at low temperatures is replaced by a dependence close to the T3-one. Besides, the usual T4-dependent redshift of the line is replaced by the T2-dependent shift. Depending on the flatness of the adiabatic surface, the latter shift may be to the red or to the blue. The theory is applied to the zero-phonon line 637 nm of the nitrogen-containing N-V center in a diamond. In this system the temperature dependence of the ZPL results from the common action of the Jahn–Teller effect and the pseudo-Jahn–Teller effect in the excited E-state: the p...

Ferroelectrics, 2001

ABSTRACT The one-magnon (1M) and two-magnon (2M) contributions were studied in optical absorption... more ABSTRACT The one-magnon (1M) and two-magnon (2M) contributions were studied in optical absorption spectra of KNiF3 single crystal, measured in the temperature range from 5 K to 300 K. The three absorption bands were considered in details. The first band is due to the magnetic-dipole transition A2g(F) → T2g(F), centred at 7700 cm, and contains the Brillouin zone-centre one-magnon contribution with the energy ω1M = 25 ± 5 cm. The other two bands are due to the electric-dipole transitions A2g(F) → Eg(D) and A2g(F) → Eg(G), centred at 16000 cm and 31200 cm, respectively. Both bands contain the Brillouin zone-boundary two-magnon contribution with the energy ω2M 813 ± 10 cm.

Chemical Physics Letters, 1985

ABSTRACT

Optical Materials, 2010

ABSTRACT In the frame of the current work novel set of Sm-doped zirconia (ZrO2) microrolls were c... more ABSTRACT In the frame of the current work novel set of Sm-doped zirconia (ZrO2) microrolls were composed by using specially modified sol–gel technique followed by annealing cycle from 500°C to 800°C. Via Raman and XRD scattering of zirconia as well as the photoluminescence (PL) spectra of the samarium ions the crystal phase formation was monitored and characterised qualitatively. The microrolls are shown first to form tetragonal phase which is stabilised by Sm ions, residual organic dopants and shear forces acting on the bent surface. The microrolls go through phase transformation to monoclinic as the annealing temperature is increased leading to partial breakup of the macroscopic structure.

Optical Materials, 2010

Composite based on TiO 2 host doped with Sm 3+ ions and co-doped with silver nanoparticles is pro... more Composite based on TiO 2 host doped with Sm 3+ ions and co-doped with silver nanoparticles is proposed as new fluorescent material. The co-doped samples were prepared from titanium alkoxide precursor by sol-gel method adjusted for addition of Sm 3+ ions and Ag nanoparticles. Commercial samarium nitrate salt and silver nanopowder (size of primary particle 30-50 nm) were used as dopant and co-dopant. Raman measurements revealed that crystalline anatase TiO 2 phase is typical for the TiO 2 :Sm 3+ films, whereas TiO 2 :Sm 3+ -Ag samples contain regions of rutile and brookite phases distributed in the predominantly amorphous TiO 2 surrounding. Samarium ions were excited either directly (k exc = 488 nm) or through the TiO 2 host (k exc = 355 nm). Enhancement of Sm 3+ fluorescence up to 20 times was revealed in the vicinity of silver aggregates. Combined plasmonic and sensitizing influences of silver on the Sm 3+ ions are considered as reasons for enhanced Sm 3+ fluorescence.

Optical Materials, 2004

Spectral and spatial properties of the excitonic luminescence of TiO 2 (anatase) waveguide layers... more Spectral and spatial properties of the excitonic luminescence of TiO 2 (anatase) waveguide layers grown by the atomic layer deposition on dielectric and metal substrates were investigated at low temperatures. Significant changes in self-trapped-excitonic (STE) spectra were observed in the direction nearly parallel to the film surface. The characteristic broad band STE emission spectrum of anatase peaking at $2.3 eV was transformed into directed spectrally narrow polarised bands. It was concluded that the leaky modes of the planar waveguide were responsible for this effect.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005

Emission, excitation and absorption spectra of HfO 2 and ZrO 2 thin films grown by atomic layer d... more Emission, excitation and absorption spectra of HfO 2 and ZrO 2 thin films grown by atomic layer deposition were investigated in the temperature range of 10-300 K. Time-resolved luminescence spectra were excited with a pulsed ArF laser and tuneable synchrotron radiation in UV-VUV. The strong emission with the peak position at 4.2-4.4 eV and with the decay time in ms range was revealed at 10 K in both materials. The emission was ascribed to the radiative decay of self-trapped excitons (STE). the features observed in the absorption and excitation spectra at 5.8 and 5.4 eV were most probably due to the formation of excitons; While the interband transitions started to dominate at 6.15 and 5.85 ev in HfO 2 and ZrO 2 , respectively.

Nature Nanotechnology, 2013

Doping of carbon nanoparticles with impurity atoms is central to their application 1,2 . However,... more Doping of carbon nanoparticles with impurity atoms is central to their application 1,2 . However, doping has proven elusive for very small carbon nanoparticles because of their limited availability and a lack of fundamental understanding of impurity stability in such nanostructures 3 . Here, we show that isolated diamond nanoparticles as small as 1.6 nm, comprising only ∼400 carbon atoms, are capable of housing stable photoluminescent colour centres, namely the silicon vacancy (SiV) 4,5 . Surprisingly, fluorescence from SiVs is stable over time, and few or only single colour centres are found per nanocrystal. We also observe size-dependent SiV emission supported by quantum-chemical simulation of SiV energy levels in small nanodiamonds. Our work opens the way to investigating the physics and chemistry of molecular-sized cubic carbon clusters and promises the application of ultrasmall non-perturbative fluorescent nanoparticles as markers in microscopy and sensing.

Nanoscale Research Letters, 2014

Silica-gold core-shell nanoparticles were used for plasmonic enhancement of rare earth fluorescen... more Silica-gold core-shell nanoparticles were used for plasmonic enhancement of rare earth fluorescence in sol-gel-derived TiO 2 :Sm 3+ films. Local enhancement of Sm 3+ fluorescence in the vicinity of separate gilded nanoparticles was revealed by a combination of dark field microscopy and fluorescence spectroscopy techniques. An intensity enhancement of Sm 3+ fluorescence varies from 2.5 to 10 times depending on the used direct (visible) or indirect (ultraviolet) excitations. Analysis of fluorescence lifetimes suggests that the locally stronger fluorescence occurs because of higher plasmon-coupled direct absorption of exciting light by the Sm 3+ ions or due to plasmon-assisted non-radiative energy transfer from the excitons of TiO 2 host to the rare earth ions.

Materials Science and Engineering: B, 2004

High-quality nanocrystalline TiO2 thin films of anatase phase were prepared by using the atomic l... more High-quality nanocrystalline TiO2 thin films of anatase phase were prepared by using the atomic layer deposition technique and implanted with Sm3+ ions. After the annealing of the films a band-to-band optical excitation of TiO2 at low temperatures led to a broadband excitonic emission superposed by a Sm3+-specific emission series of a well-pronounced fine structure. At higher temperatures (&amp;amp;amp;gt;250K) only the

Journal of Physics: Condensed Matter, 2011

This research is focused on the 4f-5d transitions in Ce 3+ centers doped into tetragonal β-SrAlF ... more This research is focused on the 4f-5d transitions in Ce 3+ centers doped into tetragonal β-SrAlF 5 single crystals belonging to the I 4 1 /a space group. The presence of four non-equivalent Sr 2+ sites in this compound leads to the appearance of three spectroscopically non-equivalent Ce 3+ luminescence centers, which can be well distinguished using a time-resolved laser spectroscopy technique. All 4f-5d transitions have slightly varying excitation and emission energies with characteristic probabilities resulting in several decay times that can be determined experimentally. One of these centers experiences strong perturbation due to a defect nearby, probably the O 2− impurity ion substituting for the F − ion and acting as a charge compensator as well. Identification of these photoluminescence centers is performed using crystal field calculations. The crystal field parameters are calculated for two identified centers using the structural data for SrAlF 5 ; diagonalization of the crystal field Hamiltonian results in obtaining the splitting of the Ce 3+ 5d states. This method allows 'regular' unperturbed Ce 3+ centers with selected Sr 2+ sites to be assigned.

Journal of Physics D: Applied Physics, 2009

ABSTRACT A systematic study of the photoluminescence spectra of samarium-doped crystalline TiO2 w... more ABSTRACT A systematic study of the photoluminescence spectra of samarium-doped crystalline TiO2 was conducted within the temperature range 10–300 K in order to reveal the energy levels of the trivalent impurity ion in different phases of titania. The sol–gel route was used to prepare Sm-doped TiO2 powders. The nanocrystalline anatase phase was obtained by annealing up to 800 °C, whereas the rutile phase was developed by annealing above 1000 °C. Crystal field calculations of Sm3+ energy levels in the two phases of TiO2 (anatase and rutile) were performed for the first time. The obtained set of energy levels assuming positioning of the Sm3+ ions in regular TiO2 lattice sites was consistent with the experimental results. The effect of the different phases of titania on the impurity is discussed.

Journal of Physics: Conference Series, 2007

Magnetic ordering in nanosized (100 and 1500 nm) nickel oxide NiO powders, prepared by the plasma... more Magnetic ordering in nanosized (100 and 1500 nm) nickel oxide NiO powders, prepared by the plasma synthesis method, was studied using Raman scattering spectroscopy in a wide range of temperatures from 10 to 300 K. It was observed that the intensity of twomagnon band decreases rapidly for smaller crystallites size. This effect is attributed to a decrease of antiferromagnetic spin correlations and leads to the antiferromagnetic-toparamagnetic phase transition .

Journal of Physics: Conference Series, 2010

Wide band-gap, high refractive index, good mechanical and high optical damage threshold are in pa... more Wide band-gap, high refractive index, good mechanical and high optical damage threshold are in particular the properties rendering zirconium oxide (ZrO 2 ) rather interesting material for various applications such as laser cavities, optical coatings, gas sensors or insulating layers in semiconductor devices. Low phonon energies (<400 cm -1 ) and wide band-gap (5.85 eV) simultaneously make ZrO 2 especially promising host for optically active dopants. Doping of ZrO 2 with various rare earth (RE) ions and creation of intrinsic defects in the pure crystal has been reported by several authors ]. In many cases, though, the nature of the excitation mechanisms leading to the emission of RE ions and intrinsic excitations is still a topic of ongoing debates ]. This is mainly because of the rather complicated electronic and phase structure caused by the dopants, ability to stabilize zirconia in tetragonal and cubic phases in addition to the only naturally stable monoclinic phase at RT. Stabilization of many of the dopants in the crystal lattice needs charge compensation, which can modify the density of states of ZrO 2 . In our work we aimed on identification of the various defect levels involved in energy-transfer processes in ZrO 2 and on revealing of different sites of optical centers by using combined excitation-emission spectroscopic studies (CEES).The investigated Sm doped bulk ZrO 2 sample was prepared by using the directional solidification of melt[ 7 ]. Phase content of the sample was determined via micro-Raman and XRD spectra. The photoluminescence (PL) measurements in the range from 3 eV to 20 eV cover both direct excitation energy range of the dopants as well as the intrinsic host absorption. Synchrotron radiation in VUV, a tuneable OPO laser and a xenon lamp were applied as excitation sources. Low temperature measurements were carried out to determine the activation energies of defect-related electronic processes. The results show that PL spectra of ZrO 2 :Sm 3+ are narrow-lined, which is typical for the f-f transitions of Sm ion in trivalent charge state. No intrinsic self-trapped exciton emission, found in high quality crystalline and thin crystalline zirconia films[ 5 ] nor various F-centre related broad band emissions, usually present in yttria-stabilized pure zirconia[ 6,8 ], were revealed in the samples even under band-to-band excitation. High dopant concentration (4 mol%), effective energy transfer to the Sm 3+ ions and rather defective structure of the mixed phase material causing appearance of efficient nonradiative decay channels are considered as main reasons of absence of intrinsic photoluminescence. Dopant-related PL was found to be many orders of magnitude more effective via band-to-band excitation of the host than through the direct intra-centre excitation of Sm 3+ ions . The presence of at least two different PL sites for the dopant ions were determined and characterized from temperature dependent CEES. Further studies using time-resolved PL spectra and decay measurements confirmed our hypotheses. Taking into account relatively good emission properties of the material, its application potential in various fields as light generation, scintillation, and gas sensing will be discussed.