D.L. Sastry

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 Eu3+ co-doped ZnO/Zn2SiO4:Mn2+ 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.

Structural and Mossbauer spectroscopic studies of heat-treated NixZn1−xFe2O4 ferrite nanoparticles

NixZn1−xFe2O4(x = 0.5,0.6,0.7) nanoparticles were prepared using coprecipitation method and were heat treated at 200, 500 and 800 °C. Structure and hyperfine interactions were studied by X-ray diffraction and Mossbauer spectroscopic techniques, respectively. The particle size increases with increasing the heat treatment (HT) temperature and Ni ion concentration. Only a quadrupole doublet was observed for Ni0.5Zn0.5Fe2O4 ferrite, heat treated at 200 °C. For higher heat treatment temperatures, hyperfine sextets appear and become predominant in nanoparticles with 800 °C HT. However, the quadrupole doublet remains with reduced intensity. The results interpreted in terms of an existence of size distribution of nanoparticles.

Effect of Cu2+ substitution on the magnetic properties of co-precipitated Ni-Cu-Zn ferrite nanoparticles

Spinel ferrite nanoparticles with chemical equation NixCu0.1Zn0.9-xFe2O4 (x = 0.5, 0.6, 0.7) have been synthsized using co-precipitation method followed by heat treatment at a temperature of 200 °C for 2h. The results of XRD, FE-SEM and VSM studies are reported. XRD patterns confirm the formation of cubic spinel phase of ferrite samples along with small amount of a secondary phase of α-Fe2O3 whose concentration decreases as Ni2+ concentration increases. The crystallite sizes (in the range of 7.5-13.9 nm) increase and the lattice parameter decreases with increase in Ni2+ ion concentration. These values are comparable to those of NiZn ferrite without Cu substitution. It has been observed that there is a considerable reduction in saturation magnetisation (Ms). This and differences in other magnetic parameters are attributed to considerable changes in cation distribution or core shell interactions of NiZn ferrite with 10 mole% Cu substitution in the place of Zn.

Superparamagnetic behavior of heat treated Mg0.5Zn0.5Fe2O4 ferrite nanoparticles studied by Mössbauer spectroscopy

Nanoparticles of Mg0.5Zn0.5Fe2O4 ferrite have been synthesized by co-precipitation method. XRD and Mossbauer spectroscopic results of Mg0.5Zn0.5Fe2O4 annealed at 200 °C, 500 °C and 800 °C are reported. It was observed that the crystallite size increases and the lattice parameter decreases with increase in annealing temperature. The observed decrease in lattice strain supports the increase in crystallite size. The Mossbauer spectra of the samples annealed at 200 °C and 500 °C exhibits superparamagnetic doublets whereas the Mossbauer spectrum of the sample annealed at 800 °C exhibits paramagnetic doublet along with weak sextet of hyperfine interaction. The values of isomer shift resemble the presence of high spin iron ions. The studied ferrite nanoparticles are suitable for biomedical applications. The results are incorporated employing core-shell model and cation redistribution.Nanoparticles of Mg0.5Zn0.5Fe2O4 ferrite have been synthesized by co-precipitation method. XRD and Mossbauer spectroscopic results of Mg0.5Zn0.5Fe2O4 annealed at 200 °C, 500 °C and 800 °C are reported. It was observed that the crystallite size increases and the lattice parameter decreases with increase in annealing temperature. The observed decrease in lattice strain supports the increase in crystallite size. The Mossbauer spectra of the samples annealed at 200 °C and 500 °C exhibits superparamagnetic doublets whereas the Mossbauer spectrum of the sample annealed at 800 °C exhibits paramagnetic doublet along with weak sextet of hyperfine interaction. The values of isomer shift resemble the presence of high spin iron ions. The studied ferrite nanoparticles are suitable for biomedical applications. The results are incorporated employing core-shell model and cation redistribution.

Effect of heat treatment on structural and Mössbauer spectroscopic properties of coprecipitated Mn0.5Ni0.5Fe2O4 ferrite nanoparticles

Results obtained in a systamatic study by X-ray diffraction and Mosssbauer spectroscopy on the structural and magnetic properties on Mn0.5Ni0.5Fe2O4 ferrite nanoparticles heat treated at 200 °C, 500 °C and 800 °C are reported. Average crystallite sizes are estimated to be in the range (2.6nm – 12.8nm). It is observed that crystallite sizes increase with increase in sintering temperature and random variation in lattice parameter was observed. At relatively low sintering temperatures the samples exhibit superparamagnetism and complete ferrite phase was observed at higher heat treatment.