CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

consists of strong band at 255 nm along with weak peaks above 350 nm and the former is
assigned to the charge transfer transition of the WO 2- 4 group whereas latter to f-f transitions
of Sm 3+ ions present in the lattice. The results are similar to that of CaWO 4 :Dy 3+ samples.
The results on CaWO 4 :Sm 3+ samples also establish that strong energy transfer takes place
from host to the Ln 3+ ions in the CaWO 4 nanoparticles. The decay curve corresponding to
4 G 5/2 level of Sm 3+ is shown in Fig.114 (d). The decay is bi-exponential in nature with
lifetime components 18.5 µs (33%) and 67.8 µs (67%).
400
Intensity (arb.units)
300
200
100
λ exc
= 253 nm
4
G 5/2
6 H 5/2
4 G 5/2
6 H 7/2
4 G 5/2
6 H 9/2
0
500 550 600 650 700
(a)
1.0
Wavelength (nm)
(b)
Intensity (arb.units)
0.8
0.6
0.4
0.2
λ em
= 602 nm
1000
0.0
1
200 250 300 350 400
0.1 0.2 0.3 0.4 0.5
Wavelength (nm)
Time (ms)
(c)
(d)
Fig.114. Emission spectrum (a) and photograph of emission (b) obtained after excitation at
253 nm from CaWO 4 : Sm 3+ nanoparticles. Corresponding excitation spectrum and
decay curve monitored at 602 nm emission are shown in Fig.114 (c and d).
Intensity (arb.units)
100
10
λ exc
= 253 nm & λ em
= 602 nm
177