Kamal P. Mani

Structural studies and luminescence properties of CeO2:Eu3+ nanophosphors synthesized by oxalate precursor method

A novel synthesis strategy to prepare CeO2:Eu3+ nanophosphors and its luminescence behavior is reported. Different structural characterization techniques such as X-ray diffraction, transmission electron microscope and thermogravimetric analysis reveal that thermal decomposition of oxalate precursor is an effective pathway to produce rare earth oxide nanocrystals. Optical characterizations of the CeO2:Eu3+ were done by UV–Visible absorption, photoluminescence excitation and emission spectra. The presence of structural defects and their role on the band gap and luminescence were discussed on the basis of absorption and emission studies. Luminescence study of the CeO2:Eu3+ ensures that the strong charge transfer band of CeO2 makes it a suitable host material for efficiently exciting Eu3+ ions by subsequent energy transfer. The dependence of luminescence efficiency of the CeO2:Eu3+ with varying concentrations of Eu3+ was also studied and discussed. The results show that Eu3+-doped CeO2 nanophosphor is a potential candidate in ultraviolet-based LEDs.

Structural and spectral investigation of terbium molybdate nanophosphor

Terbium molybdate nanophosphors were synthesized through a facile sol-gel route. The structure of the phosphors was characterized by X-ray diffraction, Raman spectra and Fourier transform infrared spectroscopy analysis. The X-ray diffraction studies revealed that the structure of the nanophosphor gradually changes from monoclinic to orthorhombic phase as heated from 700 to 900 °C. High resolution transmission electron microscopy, SAED and EDS were also employed to characterize the size, crystallinity and composition of the samples. Detailed spectroscopic investigations were carried out by Judd-Ofelt analysis based on UV-Visible-NIR absorption and emission spectra. The luminescence spectra suggest that phosphors with orthorhombic structure have better luminescence properties than the monoclinic structure. The phosphors showed intense green emission under near-UV excitation due to the energy transfer from the host lattice to Tb(3+) ions. The CIE coordinates suggest enhanced color purity for green emission and short fluorescence decay values proposes the suitability for LED applications. These phosphors can be applied as promising candidates for blue and near-UV excited WLEDs.

Synthesis, structural and spectroscopic investigations of nanostructured samarium oxalate crystals.

Nanostructured samarium oxalate crystals were prepared via microwave assisted co-precipitation method. The crystal structure and morphology of the sample were analyzed using X-ray powder diffraction, Scanning electron microscopy and Transmission electron microscopy. The presence of functional groups is ascertained by Fourier transform infrared spectroscopy. Samarium oxalate nanocrystals of average size 20 nm were aggregated together to form nano-plate structure in sub-microrange. Detailed spectroscopic investigation of the prepared phosphor material was carried out by Judd-Ofelt analysis based on the UV-Visible-NIR absorption spectra and photoluminescence emission spectra. The analysis reveals that the transition from energy level (4)G5/2 to (6)H7/2 of Sm(3+) ion has maximum branching ratio and the corresponding orange emission can be used for display applications.

Synthesis and luminescence characterization of Pr3+ doped Sr1.5Ca0.5SiO4 phosphor

Luminescence properties of Pr(3+) activated Sr1.5Ca0.5SiO4 phosphors synthesized by solid state reaction method are reported in this work. Blue, orange red and red emissions were observed in the Pr(3+) doped sample under 444nm excitation and these emissions are assigned as (3)P0→(3)H4, (3)P0→(3)H6 and (3)P0→(3)F4 transitions. The emission intensity shows a maximum corresponding to the 0.5wt% Pr(3+) ion. The decay analysis was done for 0.05 and 0.5wt% Pr(3+) doped samples for the transition (3)P0→(3)H6. The life times of 0.05 and 0.5wt% Pr(3+) doped samples were calculated by fitting to exponential and non-exponential curve respectively, and are found to be 156 and 105μs respectively. The non-exponential behaviour arises due to the statistical distribution of the distances between the ground state Pr(3+) ions and excited state Pr(3+) ions, which cause the inhomogeneous energy transfer rate. The XRD spectrum confirmed the triclinic phase of the prepared phosphors. The compositions of the samples were determined by the energy dispersive X-ray spectra. From the SEM images it is observed that the particles are agglomerated and are irregularly shaped. IR absorption bands were assigned to different vibrational modes. The well resolved peaks shown in the absorption spectra are identical to the excitation spectra of the phosphor samples. Pr(3+) activated Sr1.5Ca0.5SiO4 phosphors can be efficiently excited with 444nm irradiation and emit multicolour visible emissions. From the CIE diagram it can be seen that the prepared phosphor samples give yellowish-green emission.

Influences of Annealing Temperature and Doping Concentration on Microstructural and Optical Properties of CeO2:Sm3+ Nanocrystals

Nanocrystals of CeO2 with different doping concentrations of Sm3+ were synthesized by a novel and cost-effective method. The crystal structure, morphology and particle size were systematically investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Effects of the annealing temperature and doping concentrations on the microstructural properties of the crystals were studied. X-ray diffraction analysis indicates that the cubic structure of the CeO2 is not affected by the doping of Sm3+ up to a doping concentration of 20%. Different structural parameters such as lattice constant, surface area, bulk density and porosity of the crystal were determined and discussed. Microscopic images of the CeO2:Sm3+ suggest that the thermal decomposition of oxalate precursor is a suitable synthesis pathway to produce uniform-sized microparticles and nanoparticles. The influences of annealing temperature and doping concentration of Sm3+ on the optical properties of the nanocrystals were also discussed. The photoluminescence excitation spectra reveal that the charge transfer band is redshifted with increasing annealing temperatures. Emission attains its maximum intensity for Sm3+ concentration of 1%, and higher concentrations lead to emission quenching.