Structural, magnetic, grain and grain boundary mediated conduction features of low dimensional LaFeO3 nanoparticles.

A detailed investigation of crystal structure, magnetic and electrical conduction properties of a low dimensional LaFeO3 is reported. The sample is synthesized by Sol-Gel method with a low preparation temperature. Synchrotron x-ray diffraction, Raman and FTIR spectroscopy methods were used to establish the structural phase and vibrational modes present in the sample. The low dimensionality and morphology of the prepared sample is probed through transmission electron microscopy. From the explicitly field and temperature dependent magnetization, the magnetic phase exhibited by the nanoparticle is weak ferromagnetic which is further evidencing from the Fe57 Mossbauer spectroscopy. To gain further understanding of electrical conduction mechanism and related features of AC conductivity, impedance spectroscopy techniques are used. It is noticed that, the grain effect is dominated while the electrode effect is suppressed with temperature. The activation energies due to grain and grain boundary effect are found to be 0.0780 eV, 0.175 eV for T < 90 °C and 0.451 eV, 0.525 eV for T > 90 °C respectively. Finally, jump relaxation model and Jonscher's power law are used to explain the frequency-dependent conduction behavior in the system.

Cathodoluminescence properties of gadolinium-doped CaMoO4:Eu nanoparticles.

Gadolinium (Gd(3+)) doped CaMoO4:Eu nanoparticles were prepared via facile auto-combustion route and annealed at 900 °C for ∼4 h. X-ray diffraction study confirms the tetragonal scheelite type of CaMoO4 phase. Low voltage cathodoluminescent (CL) measurement were performed for Gd(3+) (0 and 10 at.%) co-doped CaMoO4:Eu as a function of accelerating voltage and filament current. CL studies confirm that Gd(3+) co-doped CaMoO4:Eu has a visible emission peak centered at ∼615 nm and a broad host emission band in the range 380-550 nm. Commission Internationale de L'Eclairage chromaticity diagram co-ordinates of Gd(3+) co-doped CaMoO4:Eu are found to be in reddish orange region as was observed through photoluminescence and CL spectra.

Enhanced up-conversion and temperature-sensing behaviour of Er(3+) and Yb(3+) co-doped Y2Ti2O7 by incorporation of Li(+) ions.

Y2Ti2O7:Er(3+)/Yb(3+) (EYYTO) phosphors co-doped with Li(+) ions were synthesized by a conventional solid-state ceramic method. X-ray diffraction studies show that all the Li(+) co-doped EYYTO samples are highly crystalline in nature with pyrochlore face centred cubic structure. X-ray photon spectroscopy studies reveal that the incorporation of Li(+) ions creates the defects and/or vacancies associated with the sample surface. The effect of Li(+) ions on the photoluminescence up-conversion intensity of EYYTO was studied in detail. The up-conversion study under ∼976 nm excitation for different concentrations of Li(+) ions showed that the green and red band intensities were significantly enhanced. The 2 at% Li(+) ion co-doped EYYTO samples showed nearly 15- and 8-fold enhancements in green and red band up-converted intensities compared to Li(+) ion free EYYTO. The process involved in the up-conversion emission was evaluated in detail by pump power dependence, the energy level diagram, and decay analysis. The incorporation of Li(+) ions modified the crystal field around the Er(3+) ions, thus improving the up-conversion intensity. To investigate the sensing application of the synthesized phosphor materials, temperature-sensing performance was evaluated using the fluorescence intensity ratio technique. Appreciable temperature sensitivity was obtained using the synthesized phosphor material, indicating its applicability as a high-temperature-sensing probe. The maximum sensitivity was found to be 0.0067 K(-1) at 363 K.

Synthesis, structural and luminescence properties of Mn doped ZnO/Zn2SiO4 composite microphosphor.

Manganese doped ZnO/Zn2SiO4 (MZS) composite phosphors were successfully prepared by conventional solid state reaction method. The structural and optical properties of as-prepared samples were analysed by means of XRD, SEM, PLE and PL. The result shows that the samples consist of both ZnO and ZnSiO4 phases which confirms the composite phosphor. The strain acting on the phosphor is found to be in the range of 0.0040-0.0058 for different concentration of Mn(2+) doping. The doping of Mn(2+) significantly influences the optical properties of phosphor. Under 266 nm laser excitation samples show green emission (∼530 nm) and with 355 nm laser excitation blue emission (∼441 nm) is shown. The enhancement of luminescence intensity is achieved with Mn(2+) doping up to an optimum concentration (10 at.%) and then decreases. On 266 nm excitation, blue emission intensity decreases with Mn(2+) doping. This composite phosphor shows both blue and green emission under different excitations.

White-light emitting Eu³âº co-doped ZnO/Zn2SiO4:Mn²âº composite microphosphor.

Eu(3+) co-doped ZnO/Zn2SiO4:Mn(2+) composites were synthesized via conventional solid state reaction route and were characterized by X-ray diffraction (XRD) scanning electron microscopy (SEM) and Fourier transform infra-red (FTIR) techniques. XRD studies reveal the presence of both ZnO and Zn2SiO4 phases. Photoluminescence properties of the samples were studied using 266 Nd-YAG laser excitations. Emission bands observed at ~400 nm are ascribed to ZnO phosphor. The green emission bands at 530 nm is associated with the presence of Mn(2+) ion, while orange (~583) and red (615 nm) bands are supposed to be due to the presence of Eu(3+) doped Zn2SiO4 phosphor. Energy transfer from power dependence of the sample for electric dipole transition (615 nm) was studied under 532 nm excitation by varying the power from 0.1 to 4.5 W. The estimated colour correlated temperature (CCT) values are found to be ~4875 and 4458 K under 266 nm and 532 nm laser (0.5 W) excitations. These values are close to those of tubular fluorescent or cool white/daylight compact fluorescent (CFL) (~5000 K) lamps. The present composite phosphor may have potential application in display devices.