• N V Unnikrishnan

      Articles written in Pramana – Journal of Physics

    • Optical characterization of CdSe/Dy3+-doped silica matrices

      P V Jyothy P R Rejikumar Thomas Vinoy S Kartika N V Unnikrishnan

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      Cadmium selenide nanocrystals along with dysprosium ions are doped in silica matrices through sol–gel route. The optical bandgap and size of the CdSe nanocrystals are calculated from the absorption spectrum. The size of the CdSe nanocrystallites is also evaluated from the TEM measurements. The fluorescence intensities are compared for SiO2–Dy3+ and CdSe-doped SiO2–Dy3+. The fluorescence intensity of Dy3+ is considerably increased in the presence of CdSe nanocrystals.

    • Spectroscopic properties of $Pr^{3+}$-doped erbiumoxalate crystals

      R Pragash N V Unnikrishnan C Sudarsanakumar

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      Spectroscopic properties of praseodymium ions-doped erbium oxalate ($Er_2(C_2O_4)_3 \cdot nH_2O$) crystals have been investigated. The crystals were grown by hydro silica gel method under suitable pH conditions and by single diffusion method. The well-grown crystals are bright and transparent. The dark green colour of these crystals changes with the variation of the concentrations of the dopant ions. The absorption spectra have been measured in the region 200–800 nm at room temperature. Judd–Ofelt intensity parameters for f–f transitions of the $Pr^{3+}$ ions have been determined as $\Omega_2 = 166.7$, $\Omega_4 = 1.103$ and $\Omega_6 = 2.898$. Analyses of the absorption spectra also show a possible energy transfer from the host material to the dopant.

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