Microwave resonant technique in studies of photodielectric properties of bulk, thin film and nanoparticle materials

© 2016 IOP Publishing Ltd Printed in the UK.An enhanced contactless microwave technique allows us to study the photoconductivity of materials. The transient response of the complex permittivity of matter (ϵ = ϵ1 - jϵ 2) under optical irradiation is measured with nanosecond time resolution. The main advantage of the novel methodology is the elimination of the polarization effect in evaluating photoconductivity. The potential of the methodology was demonstrated by photoconductivity measurements in Si [1 0 0] crystal, CeO2 nanocrystalline powder and Ce-doped LiYF4 single crystal. The variations of complex permittivity (δϵ1 and δϵ 2) of Si [1 0 0] crystal, CeO2 nanocrystalline powder and Ce-doped LiYF4 single crystal under optical irradiation was measured and accurate values for crystalline band gaps were extracted. Finally, quantum confinement effects were observed in nano-size crystalline powders

Entropy and Random Walk Trails Water Confinement and Non-Thermal Equilibrium in Photon-Induced Nanocavities

Molecules near surfaces are regularly trapped in small cavitations. Molecular confinement, especially water confinement, shows intriguing and unexpected behavior including surface entropy adjustment; nevertheless, observations of entropic variation during molecular confinement are scarce. An experimental assessment of the correlation between surface strain and entropy during molecular confinement in tiny crevices is difficult because strain variances fall in the nanometer scale. In this work, entropic variations during water confinement in 2D nano/micro cavitations were observed. Experimental results and random walk simulations of water molecules inside different size nanocavitations show that the mean escaping time of molecular water from nanocavities largely deviates from the mean collision time of water molecules near surfaces, crafted by 157 nm vacuum ultraviolet laser light on polyacrylamide matrixes. The mean escape time distribution of a few molecules indicates a non-thermal equilibrium state inside the cavity. The time differentiation inside and outside nanocavities reveals an additional state of ordered arrangements between nanocavities and molecular water ensembles of fixed molecular length near the surface. The configured number of microstates correctly counts for the experimental surface entropy deviation during molecular water confinement. The methodology has the potential to identify confined water molecules in nanocavities with life science importance

Vacuum-Ultraviolet and Ultraviolet Fluorescence and Absorption Studies of Er(3+)-Doped Liluf4 Single-Crystals

Journal URL: http://apl.aip.org/apl/top.js

On the interconfigurational 4f25d-4f3 VUV and UV fluorescence features of Nd3+ in LiYF4 (YLF) single crystals under F2 laser pumping

Fluorescence spectra and kinetics of LiYF4(YLF):Nd3+ single crystals pumped by an F2 pulsed discharge molecular laser at 157 nm have been obtained in the VUV and UV regions of the spectrum between 150-300 nm. With this pumping scheme some new fluorescence peaks have been observed. The high photochemical stability of this material under the above pumping scheme suggests that it can be used as an active medium for VUV tunable laser sources. ft]1|Permanent address: Kazan State University, 18 Lenin Str., 420008 Kazan, Russian Federation. © 1992

On the 4f25d → 4f3 interconfigurational transitions of Nd3+ ions in K2YF5 and LiYF4 crystal hosts

The Laser Induced Fluorescence (LIF) spectrum of K2YF5:Nd3+ (PFYK:Nd) and LiYF4:Nd3+ (YLF:Nd) single crystals, pumped by the fluorine F2 pulsed discharge molecular laser at 157.6 nm, was obtained in the Vacuum Ultraviolet (VUV) region of the spectrum. The fluorescence peaks were assigned to the 4f25d → 4f3 dipole allowed transitions of the Nd3+ ion. The 180 nm band of the LIF spectrum from the crystals indicates that the 4f25d → 4f3 dipole transitions originate from the low Stark components of the 4K11/2 level of the 4f25d configuration. The absorption spectrum of the crystal samples in the VUV was obtained as well and spectroscopic assignment of the levels of the 4f25d configuration was made. The electric crystal field splits all the levels of single and mixed configuration. The energy of the Stark components of the 4f25d configuration in YLF:Nd was shifted by few hundred cm-1 relative to that of PFYK:Nd. We observed eleven and nine dipole transitions, between the 4I9/2 ground level of the 4f3 configuration and the Stark components of the levels of the 4f25d configuration of the Nd3+ ion, in YLF and PFYK crystal hosts, respectively. © 1998 Elsevier Science B.V

Long-term oxidization and phase transition of InN nanotextures

The long-term (6 months) oxidization of hcp-InN (wurtzite, InN-w) nanostructures (crystalline/amorphous) synthesized on Si [100] substrates is analyzed. The densely packed layers of InN-w nanostructures (5-40 nm) are shown to be oxidized by atmospheric oxygen via the formation of an intermediate amorphous In-Ox-Ny (indium oxynitride) phase to a final bi-phase hcp-InN/bcc-In2O3 nanotexture. High-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy and selected area electron diffraction are used to identify amorphous In-Ox-Ny oxynitride phase. When the oxidized area exceeds the critical size of 5 nm, the amorphous In-Ox-Ny phase eventually undergoes phase transition via a slow chemical reaction of atomic oxygen with the indium atoms, forming a single bcc In2O3 phase

On the VUV and UV 4f7(8S)5d > 4f8 interconfigurational transitions of Tb3+ ions in LiLuF4 single crystal hosts

The laser induced fluorescence spectrum of Tb3+ ions in LiLuF4 single crystals, pumped by a fluorine pulsed discharge molecular laser at 157.6 nm, was obtained in the vacuum ultraviolet (VUV) and ultraviolet (UV) regions of the spectrum. The 4f75d > 4f8 dipole allowed transitions originate from the Stark components and the edge of the levels of the 4f7(8S)5d electronic configuration. The LIF spectra were interpreted on the basis of phonon trapping and phonon reabsorption within the levels of the 4f75d electronic configuration. The absorption spectrum of the crystal samples in the VUV was obtained as well. We observed eight transitions between the ground level 4f8(7F6) and the Stark components of the levels of the 4f7(8S)5d electronic configuration and five transitions between the ground level 4f8(7F6) and the Stark components of the levels of the 4f7(6P)5d electronic configuration. The edge of the levels of the 4f75d electronic configuration was found to be at 45.2 × 103 ± 0.2 × 103 cm-1 and the band gap of the crystal host was 77.6 × 103 ± 0.3 × 103 cm-1 wide. © 1998 Elsevier Science B.V. All rights reserved

VUV and UV fluorescence and absorption studies of Nd3+ and Ho3+ ions in LiYF4 single crystals

The laser induced fluorescence spectra of LiYF4:ND3+ (YLF:Nd) and LiYF4:Ho3+ (YLF:Ho) single crystals, pumped by an F2 pulsed discharge molecular laser at 157 nm were obtained in the vacuum ultraviolet (VUV) and ultraviolet (UV) regions of the spectrum. With this pumping arrangement a number of new fluorescence peaks were observed for the first time. They are assigned to the dipole allowed transitions 4f25d→4f3 and 4f95d→4f10 of the Nd3+ and Ho3+ ions, respectively. The absorption spectra of the same crystal samples in the VUV and UV spectral regions were taken as well. © 1994

Tiny Rare-Earth Fluoride Nanoparticles Activate Tumour Cell Growth via Electrical Polar Interactions

© 2018, The Author(s). Localised extracellular interactions between nanoparticles and transmembrane signal receptors may well activate cancer cell growth. Herein, tiny LaF3 and PrF3 nanoparticles in DMEM+FBS suspensions stimulated tumour cell growth in three different human cell lines (A549, SW837 and MCF7). Size distribution of nanoparticles, activation of AKT and ERK signalling pathways and viability tests pointed to mechanical stimulation of ligand adhesion binding sites of integrins and EGFR via a synergistic action of an ensemble of tiny size nanoparticles (< 10 nm). While tiny size nanoparticles may be well associated with the activation of EGFR, integrin interplay with nanoparticles remains a multifaceted issue. A theoretical motif shows that, within the requisite pN force scale, each ligand adhesion binding site can be activated by a tiny size dielectric nanoparticle via electrical dipole interaction. The size of the active nanoparticle stayed specified by the amount of the surface charges on the ligand adhesion binding site and the nanoparticle, and also by the separating distance between them. The polar component of the electrical dipole force remained inversely proportional to the second power of nanoparticle’s size, evincing that only tiny size dielectric nanoparticles might stimulate cancer cell growth via electrical dipole interactions. The work contributes towards recognising different cytoskeletal stressing modes of cancer cells

The excited state absorption from the 5d-states of Ce3+ ions in LiCaAlF6 crystals

The excited state absorption (ESA) spectra in the UV active media LiCaAlF6-Ce3+ single crystal was studied by the amplified spontaneous emission technique. The nature of the ESA spectra is discussed