Sensitizing of Sm<Superscript>3+</Superscript> fluorescence by silver dopant in the TiO<Subscript>2</Subscript> films

Composite material based on a TiO₂ matrix doped with Sm³⁺ ions and co-doped with silver was investigated. Samarium ions together with nano- and micro-aggregates of silver were incorporated into the titanium alkoxide during the sol-gel process. Samarium ions were excited either directly (λ _exc = 488 nm) or through the TiO₂ host (λ _exc = 355 nm). It was revealed that samarium fluorescence (λ _exc = 488 nm) in gelled TiO₂ films is enhanced by up to 20 times in the vicinity of silver inclusions. Sensitizing and plasmonic mechanisms of enhancement in Sm³⁺ fluorescence are discussed.     

Room Temperature Optical Thermometry Based on the Luminescence of the SiV Defects in Diamond

Optics and Spectroscopy - Diamond microcrystals containing silicon-vacancy (SiV) defects were synthesized by using a high-pressure high-temperature treatment of a mixture of pertinent...     

Polarisation dependent Raman study of single-crystal nickel oxide

The magnetic domain structure and Raman scattering have been studied in NiO single-crystals with three different (100), (110) and (111) orientations. Twin-domain structure was observed in NiO(100) and NiO(110) single-crystals using cross-polarized optical microscopy. We found that the ratio of the two-magnon (at 1500 cm⁻¹) to the two-phonon (2LO, at 1100 cm⁻¹) Raman bands intensity is sensitive in a particular way to the type of the twin-domain pattern.     

Magnetic ion exchange interactions in NiO-MgO solid solutions

In this work, a review of recent experimental data and their interpretation for Ni_cMg_1?cO solid solutions is given. In particular, the influence of exchange interactions between Ni²⁺ ions on the structural, optical, magnetic, and vibrational properties is discussed.     

Persistent spectral hole-burning in electronic tranisitions of different types of lattice defects

Abstract

With a ring dye laser persistent spectral hole-burning was measured by fluorescence excitation spectroscopy in the zero-phonon lines of the ²ll_g ? ²ll_u transition in KI:S₂ ^? and of the ³H₄ → ³P₀ transition of a defect center with three D^? ions in SrF₂:Pr³⁺:D^?and also in the zero-phonon line at 462.5 nm of a color center in neutron-irradiated and annealed α-Al₂O₃. In all three lines holes with a width in the order of 1 GHz could be obtained at 1.5 K with single frequency laser. With broad-band laser in KI:S₂ ^? and SrF₂:Pr³⁺:D^? spectral redistribution within the full range of inhomogeneous broadening could be observed which are explained by a photophysical model based on barrier crossing in asymmetric double-well-potentials. In the case of sapphire a photobleaching process is dominant which is effective also for nonselective excitation, and the holes are thermoresistant up to 300 K.     

Structural study of TiO2 thin films by micro-Raman spectroscopy

The Raman spectroscopy method was used for structural characterization of TiO₂ thin films prepared by atomic layer deposition (ALD) and pulsed laser deposition (PLD) on fused silica and single-crystal silicon and sapphire substrates. Using ALD, anatase thin films were grown on silica and silicon substrates at temperatures 125–425 °C. At higher deposition temperatures, mixed anatase and rutile phases grew on these substrates. Post-growth annealing resulted in anatase-to-rutile phase transitions at 750 °C in the case of pure anatase films. The films that contained chlorine residues and were amorphous in their as-grown stage transformed into anatase phase at 400 °C and retained this phase even after annealing at 900 °C. On single crystal sapphire substrates, phase-pure rutile films were obtained by ALD at 425 °C and higher temperatures without additional annealing. Thin films that predominantly contained brookite phase were grown by PLD on silica substrates using rutile as a starting material.     

Luminescent materials based on thin metal oxide films doped with rare earth ions

Luminescent films of TiO₂: Sm were prepared by the sol-gel method using the spray pyrolysis technique. Various techniques (including IR absorption, Raman, AFM, XPS, photoluminescence) were used to characterize the samples. After a thermal treatment up to 750°C, intense Sm³⁺ luminescence with a well-resolved fine structure was observed under optical excitation within the fundamental absorption band of the TiO₂ host. After further thermal treatments up to 950°C, the luminescence was quenched, although no anataseto-rutile phase transformation was observed. This behavior is attributed to nanocrystallinity and segregation of Sm ions in the surface layer. The text was submitted by the authors in English.     

Photoluminescence in MgxSr1−xAl2O4:Eu, Ndand electron-vibrational interaction in the Eu 5d states

Green phosphor compositions Mg_xSr_1−xAl₂O₄:Eu, Nd (with x=0.05-0.25) were prepared by solid state reaction method. The effect of Mg substitution on photoluminescence characteristics was investigated. The photoluminescence show intense green emission for MgSrAl₂O₄:Eu²⁺, Nd³⁺ with long persistence. This green emission corresponds to transitions from 4f⁶5d¹ to 4f⁷ of Eu²⁺ ion. Comparative analysis of the excitation and emission spectra were used to evaluate the crystal field splitting of the 5d states of Eu²⁺ and the parameters of electron-vibrational interaction, such as Huang-Rhys factor, effective phonon energy, and zero-phonon line position.     

Calculations of physical properties of pure and doped crystals: Ab initio and semi-empirical methods in application to YAlO3:Ce and TiO2

In this paper we demonstrate that two independent methods of calculations (DFT based ab initio and semi-empirical crystal field theory) can be used to form a complementary picture of the optical and electronic properties of the doped host and impurity ion. The crystals considered in the present paper are: (i) YAlO₃:Ce³⁺ and (ii) two dominant phases of TiO₂—rutile and anatase. As an example, detailed calculations of the band structure and crystal field energy level scheme of YAlO₃:Ce³⁺ are reported. From the analysis of the band structure and density of states, the character of the YAlO₃ energetic bands and positions of the Ce impurity energy levels were established. It was also shown how the ab initio methods can be used for calculations of the structural properties of solids under elevated pressure. Taking the two dominant phases of TiO₂ as an example, it was demonstrated how the elastic properties can be extracted from the calculated unit cell’s volume at different pressures. Particular attention was paid to the microscopic effects of crystal field, which were evidenced by the pressure-induced changes of the structure and shape of distribution of the Ti 3d electrons density of states. It was demonstrated how the difference in crystal structure of the anatase and rutile phases leads to remarkable difference in microscopic crystal field effects, which was explained by different Ti-O distances in both phases. In addition, the pressure dependence of the band gaps for anatase and rutile was investigated. It was shown that the hydrostatic pressure leads to the band gap narrowing in anatase and band gap widening in rutile, with pressure coefficients +0.00681 eV/GPa for rutile and −0.0088 eV/GPa for anatase.