CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

Strong green emission has been observed from Tb 3+ doped CaWO 4 nanoparticles in methanol
after exciting at 253 nm (Fig.112 (b)). Excitation spectra corresponding 545 nm emission is
shown in Fig.112 (c) and consist of a strong peak between 230 and 300 nm, with a maximum
~260 nm along with less intense sharp peaks above 300 nm. The strong band is due to the
overlap of host absorption and 4f-5d transition of Tb 3+ ions present in the lattice. Sharp peaks
above 300 nm are assigned to f-f transitions of Tb 3+ ion. The decay curve corresponding to
5 D 4 level of Tb 3+ is shown in Fig.112 (d). The decay curve is bi-exponential in nature with
lifetime components 0.978 ms (23%) and 1.59 ms (77 %). The shorter and longer lifetime
component has been attributed to the surface and bulk Tb 3+ ions, respectively present in the
nanoparticles.
6.8. Luminescence studies on Dy 3+ doped CaWO 4 nanoparticles: Emission spectrum from
2 at % Dy 3+ doped CaWO 4 nanoparticles obtained after exciting the sample at 253 nm is
shown in Fig.113 (a). It consist of peaks at 478, 574 and 665 nm and are due to 4 F 9/2 Æ
6 H 15/2 , 4 F 9/2 Æ 6 H 13/2 and 4 F 9/2 Æ 6 H 9/2 transitions, respectively of Dy 3+ ions present in the
lattice. Strong greenish yellow emission is observed from the Dy 3+ doped CaWO 4
nanoparticles in methanol after exciting at 253 ( Fig.113 (b)). Excitation spectrum
corresponding to 574 nm emission of Dy 3+ is shown in Fig.113 (c). The spectrum consists of
a strong band at 253 nm along with weak peak at 350 nm and the latter is due to f-f transition
of Dy 3+ ion. The strong band is characteristic of the host and is arising due to charge transfer
absorption of host as there is no absorption band for Dy 3+ in this region. Observation of host
absorption peak in the excitation spectrum corresponding to Dy 3+
emission at 574 nm
confirms that the absorbed energy of the host get transferred to Dy 3+ ions. The decay curve
corresponding to 4 F 9/2 excited state of Dy 3+ is shown in Fig.113 (d). The decay is found to be
bi-exponential with lifetime components 0.1 ms (24%) and 0.36 ms (76%). Similar to the
explanation given to the 5 D 4 decay of Tb 3+ from CaWO 4 :Tb 3+ nanoparticles, the faster and
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