Issue No. 1, April

Abstract

In the presented work composite ferroelectric/ferrimagnetic ceramics have been obtained and described. The investigated material is based on PMN-PT powders and Ni-Zn ferrite powder. The Powders of ferroelectric component (i.e. (1–x)PMN-(x)PT with x from 0.25 to 0.40 with step 0.03 were synthesized using the sol-gel method. The magnetic component i.e. nickel-zinc ferrite was obtained from oxides using the classic method of obtaining ceramics. The compositions of PMN–PT used by us have rhombohedral or tetragonal symmetries, or belong to morphotropic region. The final ceramic composite samples were obtained using the classic method of ceramic technology with calcination route and final pressureless densification using free sintering. In this paper, XRD, EDS dielectric and magnetic properties have been investigated and described for the obtained composite ceramic samples.

Abstract

In this paper ferroelectric–ferromagnetic composites based on a doped PZT-type and ferrite powders are presented. Ferroelectric powder (in amount of 85.0 wt-%) was based on multicomponent PZT-type materials: i) Pb(Zr_0.51Ti_0.49)O₃+0.2%at.Bi₂O₃+ 0.03%at.Nb₂O₅+0.06%at.MnO₂,ii) Pb_0.84Ba_0.16(Zr_0.54Ti_0.46)O₃+1.0%at.Nb₂O₅, while nickel–zinc ferrite Ni_0.64Zn_0.36Fe₂O₄ (in amount of 15.0 wt-%) served as the magnetic component of the composite samples. The synthesis of the ferroelectric–ferromagnetic composite powders was performed by solid state, while final densification of the synthesized powders was achieved by free sintering. Conducted tests indicate obtained ferroelectromagnetic ceramic composites (PZT-ferrite type) to exhibit good properties giving the possibility for their use as magnetoelectric transducers.

Abstract

In this paper we report on the fabrication and the characterization of colloidal systems considering complementary structures based on responsive artificial opal both in direct and inverse configuration. We will discuss alternative systems such as: (i) chromatic composite structure as chemical sensor based on polystyrene (PS) nanoparticles (NPs) embedded in elastomeric matrix, where the application of specific organic solvents produces a variation of its color; (ii) metallic dielectric structures, where the infiltration of colloidal crystals with metallic nanoparticles permits to modify the optical properties of the common opal and can be usefully exploited as SERS substrates; (iii) inverse silica opal functionalized with fluorescent aptamers in order to develop biosensors in dye labelled fluorescence detection scheme.

Abstract

We report on the structural characterization and the photovoltaic performances of novel photoelectric conversion materials fabricated by simplified and cheap procedures based on a chemical approach. Our prepared composite microparticles were composed of fluorosilicate/phosphorus oxide holding together by ammonium. When such composite microparticles were used in the active layer of the hybrid solar cells, the relatively high J_sc was obtained by causing the adequate carrier transport from the active layer to each electrode, attaining the best photovoltaic performance with a PCE of 4.45 %. These findings indicate that the fluorosilicate/phosphorus oxide composite microparticles have sufficient ability as the photoelectric conversion materials.

Abstract

Phosphor materials have fascinating applications in the field of photovoltaic and biosensors but low quantum yield is a major hurdle in their applications. In this paper, the influence of surface plasmon on the photoluminescence is investigated with surface modified YAG:Ce³⁺-Yb³⁺ coupled with spherical gold nanoparticles. The YAG:Ce³⁺-Yb³⁺ photoluminescence band ratio Yb/Ce rise from 0.25 to 0.32 with the plasmon effects. For the photoluminescence, the decay time of Ce reduces from 31.9 ns to 29.9 ns while for Yb from 54.2 ms to 52.0 ms respectively. Further, the plasmon absorption peak is also observed in the spectra of YAG:Ce³⁺-Yb³⁺/Au nanoparticles system. The results indicate that the field inside the phosphors has been modulated with surface plasmon of gold nanoparticles.

Abstract

Indium phosphide (InP) quantum dots (QDs) with luminescence tunable over the entire visible spectrum were prepared by the conventional hot injection method. InP QDs are considered alternatives to Cadmium containing QDs for application in light-emitting devices because of showing similar optical properties to those containing toxic heavy metals. The multishell coating was shown to improve the photoluminescence quantum yield (QY) of InP QDs more strongly than the conventional ZnS shell coating. QY values were more than 60% along with FWHM of 41-73 nm can be routinely achieved, making the optical performance of InP/ZnS/ZnS or InP/ZnS/SiO₂ QDs comparable to that of InP/ZnS QDs. These QDs and the polymer dissolved in the appropriate solvent and deposited by casting to give homogeneous films and showed a good level of dispersion of the QDs within the polymer.

Abstract

Recent progress of transparent ceramic scintillators is reviewed. The present work reports the research and development of oxide transparent ceramic materials such as garnet, sesquioxide, complex perovskite and some other kinds. Some representative scintillation properties such as scintillation emission spectra and decay times under X-ray irradiation are presented. Gamma-ray induced scintillation detector properties including pulse height spectrum, energy resolution, and light yield nonproportionality are also shown.

Abstract

X-ray imaging represents a very relevant tool in basic and applied research fields due to the possibility of performing non-destructive investigations with high spatial resolution. We present innovative X-ray imaging detectors based on visible photoluminescence from aggregate electronic defects locally created in lithium fluoride (LiF) during irradiation. Among the peculiarities of these detectors, noteworthy ones are their very high spatial resolution (intrinsic ̴̴ 2 nm, standard ̴̴ 300 nm) across a large field of view (>10 cm²), wide dynamic range (>10³) and their insensitivity to ambient light. The material photoluminescence response can be enhanced through the proper choice of reflecting substrates and multi-layer designs in the case of LiF films. The present investigation deals with the most appealing X-ray imaging applications, from simple lensless imaging configurations with commonly-available laboratory polychromatic X-ray sources to X-ray imaging-dedicated synchrotron beamlines in absorption and phase-contrast experiments.

Abstract

In the present work the influence of co-doping with ytterbium ions (for 0, 0.5, 1.5, 2.5 wt.% of Yb³⁺) on physical properties of 8/65/35 PLZT was studied. The ceramic powders were synthesized by the modified sol-gel method, and underwent consolidation by the pressure-less sintering techniques, in Ts=1200°C/6h. Our investigations give a detailed account of the relationships between concentrations of trivalent ytterbium ions in PLZT matrix, on their structure, microstructure, as well as luminescence properties. Near-infrared luminescence spectra at about 1020 nm were registered, which correspond to ²F_5/2 - ²F_7/2 transition of Yb³⁺. Based on decay measurements, the luminescence lifetimes for the ²F_5/2 excited state of Yb³⁺ were determined. Luminescence decay analysis indicates that the ²F_5/2 lifetime increase with increasing activator concentration (Yb³⁺) in PLZT ceramic matrix.

Abstract

In this study, lanthanide elements (Ln³⁺) and 2,3,5,6-tetrafluoro-1,4-benzenedicarboxylic acid (TFBDC) based metal-organic frameworks (MOFs) were synthesized by precipitation and diffusion-controlled precipitation methods. Powders insoluble in aqueous media and polar solvents were obtained. The microstructure and properties of Ln³⁺ MOFs were evaluated and discussed. X-ray diffraction (XRD) analysis, infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and fluorescence spectroscopy (FLS) were carried out to characterize Ln³⁺ MOF's crystallinity, the microstructure, chemical composition and optical properties.

Abstract

The aim of this work was to obtain Pb_0.92(La_0.08)(Zr_0.65Ti_0.35)_0.98O₃ materials co-doped with two different lanthanide ions (Ln³⁺) and determine how they influence the physical properties of prepared 8/65/35 PLZT: Ln³⁺ ceramics. As a co-dopant, praseodymium (Pr³⁺) and neodymium (Nd³⁺) ions were used at the concentration of 0.0 and 0.5 wt.% respectively. The ceramic powders of 8/65/35 PLZT, PLZT:Pr³⁺ as well PLZT:Nd³⁺ were synthesized by the conventional ceramic route, from high purity raw oxide materials (>99,9%). All compositions were sintered at Ts=1200°C/3h, by the uniaxial hot pressing. Performed measurements have shown dependence of used dopant on structure, microstructure, dielectric and optical properties of the 8/65/35 PLZT: Ln³⁺ materials.

Abstract

Lithium fluoride (LiF) is a well-known dosimeter material and is sensitive to any kind of ionizing radiation. A linear accelerator for protontherapy under development at ENEA C.R. Frascati was used to irradiate LiF crystals and thin films at room temperature with proton beams of 3 and 7 MeV energy in a dose range from 10³ to 10⁷ Gy. The irradiation of LiF induced the formation of stable F₂ and F₃ + color centers (CCs), which emit with broad photoluminescence (PL) bands under optical pumping at wavelengths close to 450 nm. By acquiring the PL image of the irradiated spots with a conventional fluorescence microscope, the transversal proton beam intensity was mapped with a high spatial resolution. The integrated PL intensity was also measured as a function of the irradiation dose: LiF films showed a linear PL response extending over three orders of magnitude of dose range, independently on the beam energy. It was also possible to measure the CCs PL distribution with proton penetration depth and direct imaging the Bragg peak, which gives an estimate of the proton beam energy. The sensitivity of the optical reading techniques and the high emission efficiency of CCs provided encouraging results to use photoluminescent color-center LiFbased radiation detectors for proton beam dosimetry and imaging applications.