CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

lattice. Lanthanide ions occupying such a low symmetry environments (coordination number
4) in inorganic hosts is observed for the first time.
100
SbPO 4
70
% Transmittance
75
50
25
0
SbPO 4
:Tb 3+ (1%)
SbPO 4
:Tb 3+ (2.5%)
SbPO 4
:Tb 3+ (5%)
600 800 1000 1200 1400
Wavenumber (cm -1 )
% Transmittance
60
50
40
30
20
SbPO 4
SbPO 4
: Tb 3+ (1%)
SbPO 4
: Tb 3+ (2.5%)
SbPO 4
: Tb 3+ (5%)
10
600 620 640 660 680 700
Wavenumber (cm -1 )
(a)
(b)
Fig.70. FT-IR patterns corresponding to SbPO 4 nanoribbons/ nanoparticles containing
different concentrations of Tb 3+ ions. The peak corresponding to the Sb-O stretching
vibration in these samples observed over the region of 600-700 cm -1 is shown in
Fig.70 (b).
The effect of SiO 2 coating is very clearly seen in the symmetric PO4 stretching mode
at ~ 930 cm -1 (Fig.71). The peak at ~930 cm -1 for undoped SbPO 4 and
3+
SbPO4:Ce (2.5%),Tb 3+ (5%) sample remains unchanged. The increased width in silica coated
3+
SbPO4:Ce (2.5%),Tb 3+ (5%) sample is due to random distribution of phosphate structural
units in the SiO 2 matrix. The presence of Si attached with the PO4 tetrahedra (P-O-Si
linkages) results in weakening of the ν sym vibrational group frequencies at ~930 cm -1 . In fact,
a careful analysis of the 930 cm -1 peak (Fig.71 (c)) indicates that there are two overlapping
peaks, one at ~930 cm -1
similar to what is observed for the undoped and
3+
SbPO4:Ce (2.5%),Tb 3+ (5%) sample and another at ~ 921 cm -1 which represent the changed
bonding configuration of the PO 4 units in the silica matrix. Thus, the phosphate groups are
present in two different environments. One such possible change in the bonding environment
is the terminal O atoms of surface PO tetrahedron of SbPO nanoribbons/ nanoparticles
4 4
125