CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

eing bonded with the Si atoms (i.e. P-O-Si type of linkages). Phosphorus being more
electronegative than Si, this will result in a reduction in the force constants, and hence
lowering of Raman frequency. This effect is more prominent for the symmetric PO 4 vibration
and hence we observe two peaks in the present case.
Intensity (arb. units)
(a)
(b)
(c)
880 900 920 940 960
Raman shift (cm -1 )
Fig.71 Raman spectrum corresponding to symmetric PO 4 stretching mode of (a) un-doped
3+
3+ 3+
SbPO4 (b) SbPO 4 :Ce (2.5%),Tb (5%) and (c) SbPO 4 :Ce (2.5%),Tb 3+ (5%) samples
dispersed in silica.
4.3.5 Luminescence studies on SbPO 4 :Ce, Tb and effect of incorporation of
nanomaterials in silica: Figure 72 shows the emission spectra of SbPO :Tb 3+
4 (5%),
3+
SbPO4:Ce (2.5%),Tb
3+ 3+
(5%) and SbPO 4 :Ce (2.5%),Tb 3+ (5%)-SiO 2 obtained after 250 nm
excitation. The peaks observed ~ 489, 543, 585, and 621 nm correspond to transitions from
5 D 4 level to 7 7 7 F 6, F 5, F 4 and 7 F levels, respectively of Tb 3+
3 ion. It is worth noting that, unlike
Tb 3+ or Ce 3+ -Tb 3+ doped SbPO 4 samples, pure TbPO4 prepared by the identical method as
that of SbPO :Tb 3+
4 samples did not show any emission (inset of Fig.72). This aspect
substantiate the fact that Tb 3+ ions are getting incorporated in SbPO 4 lattice and do not exist
as separate TbPO 4 phase, a fact which is also confirmed from the vibrational studies
described above. It is also observed that Ce 3+ ion shows very weak emission in the UV
3+ 3+
region. A representative Ce emission spectrum from SbPO 4 :Ce (2.5%),Tb 3+ (5%) sample
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