H. Padma Kumar

Optical properties of nanocrystalline HfO2 synthesized by an auto-igniting combustion synthesis

Abstract The optical properties of nanocrystalline HfO2 synthesized using a single-step auto-igniting combustion technique is reported. Nanocrystalline hafnium oxide having particle size of the order 10–15 nm were obtained in the present method. The nanopowder was characterized using X-ray diffraction, Fourier transform infrared and Fourier transform Raman spectroscopic studies. All these studies confirm that the phase formation is complete in the combustion synthesis and monoclinic phase [P21/c(14)] of HfO2 is obtained without the presence of any impurities or additional phases. The powder morphology of the as-prepared sample was studied using transmission electron microscopy and the results were in good agreement with that of the X-ray diffraction studies. The optical constants such as refractive index, extinction coefficient, optical conductivity and the band gap were estimated from UV–vis spectroscopic techniques. The band gap of nanocrystalline HfO2 was found to be 5.1 eV and the sample shows a broad PL emission at 628 nm. It is concluded that the transitions between intermediate energy levels in the band gap are responsible for the interesting photoluminescent properties of nanocrystalline HfO2.

Spectroscopic Investigations on Ln(Zr1/3Ti2/3)TaO6 (Ln = Ce, Pr, Nd and Eu) Ceramics

In the present work, the authors have performed vibrational spectroscopic study of Ln(Zr1/3Ti2/3)TaO6 (Ln = Ce, Pr, Nd and Eu) ceramics by analyzing their Raman spectra. An attempt is made to correlate the structure and microwave dielectric properties of the samples with their vibrational spectroscopic characteristics. The Raman spectra are analyzed mainly on the basis of TaO6 octahedra. Zr substitution in LnTiTaO6 has not changed the prominent phase, however, the movement towards euxenite structure with increase in atomic number of the lanthanide has become faster. The broadening and splitting of lines observed in Nd and Eu based compounds indicate the distortion of octahedra. The negative value of τf of Eu based compounds indicates the presence of euxenite phase in addition to the prominent aeschynite phase. This is confirmed by the maximum distortion of the octahedra as indicated by the lower wavenumber, broadening and splitting of the characteristic Raman lines. The Raman shift of υ2(Eg) mode showed a...

Photoluminescent properties of Pr3+ doped YTiAO6 (A= Nb&Ta) euxenite compounds

Pr3+ doped YTiAO6 (A = Nb and Ta) compounds were prepared by conventional solid state ceramic route. X – ray diffraction studies of the samples confirmed the euxenite orthorhombic phase formation. Effect of Pr3+ doping on the optical and luminescence properties of YTiAO6 (A = Nb and Ta) were studied. The strong absorption in the UV region are due to the absorption by the host YTiAO6 (A = Nb and Ta) and all other peaks can be attributed to that of Pr3+. Host emission peaks are observed around 485 nm and 460 nm in all samples. The red emission observed at 614 nm in the doped samples corresponds to the 1D2 to 3H4 transition of Pr3+ ion. CIE colour coordinates and chromaticity values were also discussed.Pr3+ doped YTiAO6 (A = Nb and Ta) compounds were prepared by conventional solid state ceramic route. X – ray diffraction studies of the samples confirmed the euxenite orthorhombic phase formation. Effect of Pr3+ doping on the optical and luminescence properties of YTiAO6 (A = Nb and Ta) were studied. The strong absorption in the UV region are due to the absorption by the host YTiAO6 (A = Nb and Ta) and all other peaks can be attributed to that of Pr3+. Host emission peaks are observed around 485 nm and 460 nm in all samples. The red emission observed at 614 nm in the doped samples corresponds to the 1D2 to 3H4 transition of Pr3+ ion. CIE colour coordinates and chromaticity values were also discussed.