T. N. Fursova

Advantages and Problems of Nanocrystalline Scintillators

Our experiments with nanocrystalline scintillating rare earth oxides and rare earth fluorides have shown that in some cases nanoscopic dimensions provide essential improvement of the most important scintillation parameters: light yield, kinetics of scintillations, radiation hardness, etc. We found that in the range from 20 to 100-nm of the oxide and fluoride particles there are 3 types of layered structures: with expanded exterior layer, with changed phase structure, and with changed chemical composition. These layered structures can strongly influence scintillation parameters: cause an increase or decrease in the light yield, vary scintillation kinetics, modify radiation hardness, etc. Control of dimensions and structures of nanoscintillators can be used for significant modifications of parameters of radiation detectors (radical acceleration of kinetics, enhancement of light yield, increase in radiation hardness, etc.). Radiation detectors based on nanoscintillators have promising prospects for applications in new generations of devices for medical diagnostics, security inspection, radiation monitoring of nuclear reactors.

IR-active optical phonons in Pnma-1, Pnma-2 and R3¯c phases of LaMnO3+δ

Infrared-active phonons in LaMnO3+δLaMnO3+δ were studied by means of the reflection and transmission spectroscopy from 50 to 800cm-1 at room temperature. Powder and ceramic samples of the phases of Pnma-2(δ=0.02),Pnma-1(δ=0.08) and R3¯c(δ=0.15) were investigated. In addition, energies of the dipole-active phonons in Pnma-2, Pnma-1 phases were obtained by lattice-dynamics calculations. The transformations of IR-active phonons with the increase in δδ in the sequence of Pnma-2, Pnma-1, R3¯c are discussed.

Optical phonon spectra of PbF2 single crystals

The spectra of dipole-active optical phonons are measured for the cubic and orthorhombic phases of PbF2 single crystals. The frequencies and eigenvectors of normal modes in the Pnma orthorhombic phase are calculated. It is found that the spectrum of the cubic phase exhibits excess vibrational modes of the PbF2 orthorhombic phase.

Photoinduced light absorption by C60 films in the 0.08-4.0-eV spectral range

Spectra of photoinduced light absorption in C60 films at high and low excitations in the temperature range between 15 and 300 K have been measured. In addition to the well-known explanation of photoinduced absorption in terms of optical transitions in the system of photogenerated singlet excitons, triplet excitons, and polarons, changes in the absorption spectrum of the fullerite ground state must be considered. We suggest taking into account the effect of crystal field in explaining the features of the photoinduced absorption spectrum. A feature similar to the inverted luminescence spectrum and ascribed to optical excitation of singlet excitons, which is partially allowed owing to intermolecular interaction, has been detected in spectrum of photoinduced absorption.

Properties of a composite material based on multi-walled carbon nanotubes and an ionic liquid

A solid-phase composite material based on multi-walled carbon nanotubes and an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) has been synthesized. It has been found using infrared spectroscopy that vibrational modes of the ionic liquid are shifted by 4–12 cm−1 toward lower energies with respect to those observed in the initial fluid due to the interaction of ionic liquid molecules with the nanotubes. Electron microscopy has revealed that, in the composite, the ionic liquid is present on the surface of nanotubes and partially inside them. It has been shown that the degree of extraction of lanthanides from aqueous solutions with the use of the synthesized composite increases with increasing content of the ionic liquid in it.

Synthesis of a periodic SiC/C nanostructure

Highly porous periodic structures consisting of a three-dimensional replica of pores in the initial opal lattice have been synthesized by high-temperature thermochemical treatment of opal matrices filled with carbon compounds, followed by dissolution of silicon dioxide. It has been shown that the main phases of the composite are carbon and silicon carbide. Based on the X-ray diffraction, Raman, and IR spectroscopy data, it has been assumed that the composite contains fragments of hexagonal diamond. The photoluminescence and optical reflection spectra of the composites have been measured.

Spectral and structural features of Lu1 − xRExBO3 compounds

The luminescence spectra, luminescence excitation spectra, IR absorption spectra, and crystal structure of orthoborates Lu1 − xRExBO3 (RE = Eu, Gd, Tb, Y, Dy) have been investigated. It has been found that the solid solution consisting of a LuBO3 orthoborate, which has two stable structural modifications (calcite and vaterite), and an REBO3 orthoborate, which has one structural modification (vaterite), crystallizes only in the vaterite structure when the concentration of a rare-earth ion substituting for lutetium exceeds 15–20 at %. The investigation of the photoluminescence spectra has demonstrated that, for rare-earth ions Lu3+, Eu3+, Y3+, and Gd3+ in the vaterite modification of Lu1 − xRExBO3 orthoborates, there are at least two positions that are not equivalent in the symmetry of the local environment. It has been established that the maximum intensity of the luminescence of the vaterite modification of Lu1 − xTbxBO3 compounds synthesized at 970°C, which is observed at a terbium concentration of 15 at %, is several times higher than the maximum intensity of the luminescence of the calcite modification.

Growth of ZnO nanocrystals by pulsed laser deposition on sapphire and silicon and the infrared spectra of the nanocrystals

The ZnO nanorods that comprise highly oriented nanorod structures are grown on sapphire and silicon substrates by laser ablation. The nanostructures grown in different conditions are characterized by means of electron microscopy and Fourier infrared reflectance spectroscopy. The contributions of optical phonons and free charge carriers to the infrared spectra of the layers of ZnO nanorods are identified, and the degree of orientation of the ZnO nanorods with respect to the substrate surface is analyzed in relation to the conditions of growth. Softening of optical phonons of ZnO with decreasing the nanorod diameter is observed.

Spectral characteristics and energy transfer from Ce3+ to Tb3+ in compounds Lu1 – x – yCexTbyBO3

The structure, IR absorption spectra, morphology, and spectral characteristics of compounds Lu1 – x – yCexTbyBO3 have been investigated. It has been shown that the Tb3+ luminescence excitation spectrum of the Lu1 – x – yCexTbyBO3 compounds is dominated by a broad band coinciding with the excitation band of Ce3+ ions, which clearly indicates energy transfer from the Ce3+ ions to the Tb3+ ions. The spectral position of this band depends on the structural state of the sample: in the structures of calcite and vaterite, the band has maxima at ~339 and ~367 nm, respectively. By varying the ratio between the calcite and vaterite phases in the sample, it is possible to purposefully change the Tb3+ luminescence excitation spectrum, which is important for the optimization of the spectral characteristics of Lu1 – x – yCexTbyBO3 when it is used in light-emitting diode sources. An estimate has been obtained for the maximum distance between Ce3+ and Tb3+ ions, which corresponds to electronic excitation energy transfer. It has been shown that the high intensity of Tb3+ luminescence in these compounds is due to the high efficiency of electronic excitation energy transfer from the Ce3+ ions to the Tb3+ ions as a result of the dipole–dipole interaction.

Influence of nanoparticles of cesium sulfate and deformation on structure, vibration spectra, and luminescence of polystyrene

Significant changes in infrared absorption spectra of polystyrene upon the addition of cesium sulfate nanoparticles to it are observed, which is due to two variants of attachment of organic molecules to nanoparticles (through hydrogen and pi bonds). The relation between the bonds changes significantly during deformation of polystyrene/cesium sulfate composite owing to differences in the mechanical strength thereof. In its turn, the differences in atomic and electronic bond structures result in a significant differentiation of their influence on light emission processes, making it possible to control the scintillation characteristics of polystyrene/nanoparticle composites via regulating their composition and morphology.