CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

have noticed that the peak maximum at ~ 1053 cm -1
characteristic of the asymmetric
stretching vibration of PO 4 structural units, decreases with doping lanthanide ions in the
SbPO 4 lattice, as can be seen from Fig.69 (b). Shifting of the peak maximum corresponding
to the asymmetric P-O stretching mode of PO 4 units to lower wave numbers has been
3+ 3+ 3+
attributed to the combined effect of heavier mass of Ce and Tb ions compared to Sb ion
3+ 3+
and decrease in the covalency of P-O linkages brought about by replacement of Sb by Ce
and Tb 3+ ions in SbPO lattice. 4
Normalised intensty
1.0
0.8
0.6
0.4
0.2
0.0
SbPO 4
SbPO 4
:Ce 3+ (2.5),Tb 3+ (5%)
Normalised intensity
0.6
0.5
0.4
0.3
0.2
0.1
SbPO 4
:Ce 3+ (2.5%),Tb 3+ (5%)-SiO 2
SbPO 4
:Ce 3+ (2.5%),Tb 3+ (5%)
SbPO 4
SbPO 4
:Ce 3+ (2.5%),Tb 3+ (2.5%)-SiO 2
0.0
200 400 600 800 1000 1200
Ramanshift (cm -1 )
(a)
(b)
1050
Raman shift (cm -1 )
Fig.69. Raman spectrum over the entire region (a) corresponding to un-doped SbPO 4 ,
3+
3+ 3+
SbPO4:Ce (2.5%),Tb (5%) and SbPO 4 :Ce (2.5%),Tb 3+ (5%) samples dispersed in
silica. The peak corresponding to the asymmetric stretching vibrations of PO 4
tetrahedra in these samples observed over the region of 1000-1080 cm -1 is shown in
Fig.69 (b).
Similar trend is also observed for the asymmetric stretching vibration of the PO 4 units
in the IR spectrum (Fig.70 (a)). In addition to the vibrations of PO 4 stretching, the vibrations
characteristic of Sb-O linkages (peak observed ~ 640 cm -1 ) is also affected (Fig.70 (b)). The
peak at 640 cm -1 shows a systematic lowering with increase in lanthanide ion concentration in
SbPO 4 . This is not very clear in the Raman spectrum due to weak intensity for peak
corresponding to Raman mode of Sb-O linkages. Hence based on the IR and Raman studies it
3+ 3+
is established that lanthanide ions such as Ce and Tb replace Sb 3+ ions in the SbPO 4
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