• R P S Chakradhar

      Articles written in Bulletin of Materials Science

    • Optical absorption and fluorescence properties of Er3+ in sodium borate glass

      Y C Ratnakaram J Lakshmi R P S Chakradhar

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      Spectroscopic properties of Er3+ ions in sodium borate glass have been studied. The indirect and direct optical band gaps (𝐸opt) and energy level parameters (Racah (𝐸1, 𝐸2 and 𝐸3), spin-orbit (𝜉4f) and configurational interaction (𝛼)) are evaluated. Spectral intensities for various absorption bands of Er3+ doped sodium borate glass are calculated. Using Judd–Ofelt intensity parameters (𝛺2, 𝛺4, 𝛺6), radiative transition probabilities (𝐴), branching ratios (𝛽) and integrated absorption cross sections (𝛴 ) are reported for certain transitions. The radiative lifetimes (𝜏R) for different excited states are estimated. From the fluorescence spectra, the emission cross section (𝜎p) for the transition, ${}^{4}I_{13/2} \rightarrow {}^{4}I_{15/2}$ is reported.

    • Spherical and rod-like Gd2O3:Eu3+ nanophosphors—Structural and luminescent properties

      N Dhananjaya H Nagabhushana B M Nagabhushana B Rudraswamy C Shivakumara R P S Chakradhar

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      A comparative study of spherical and rod-like nanocrystalline Gd2O3:Eu3+ (Gd1.92Eu0.08O3) red phosphors prepared by solution combustion and hydrothermal methods have been reported. Powder X-ray diffraction (PXRD) results confirm the as-formed product in combustion method showing mixed phase of monoclinic and cubic of Gd2O3:Eu3+. Upon calcinations at 800°C for 3 h, dominant cubic phase was achieved. The as-formed precursor hydrothermal product shows hexagonal Gd(OH)3:Eu3+ phase and it converts to pure cubic phase of Gd2O3:Eu3+ on calcination at 600°C for 3 h. TEM micrographs of hydrothermally prepared cubic Gd2O3:Eu3+ phase shows nanorods with a diameter of 15 nm and length varying from 50 to 150 nm, whereas combustion product shows the particles to be of irregular shape, with different sizes in the range 50–250 nm. Dominant red emission (612 nm) was observed in cubic Gd2O3:Eu3+ which has been assigned to ${}^{5}D_{0} \rightarrow {}^{7}F_{2}$ transition. However, in hexagonal Gd(OH)3:Eu3+, emission peaks at 614 and 621 nm were observed. The strong red emission of cubic Gd2O3:Eu3+ nanophosphors by hydrothermal method are promising for high performance display materials. The variation in optical energy bandgap (𝐸g) was noticed in as-formed and heat treated systems in both the techniques. This is due to more ordered structure in heat treated samples and reduction in structural defects.

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