CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

chemical shift anisotropy is much higher and the value significantly increases with increase
in Eu 3+ content in the sample (viz. Table 6). Comparable values of chemical shift anisotropy
for both GaPO 4 and 2.5 at % Eu 3+ incorporated GaPO4 nanoparticles, further confirm the
absence of P-O-Eu 3+ linkages in the sample. In other words Eu 3+ ions are not in the near
vicinity of P and must be in the vicinity of Ga 3+ ions, as Ga-O-Eu linkages formed by
undergoing surface ion exchange with protons of the Ga-OH linkages. For GaPO 4
nanoparticles with higher Eu 3+ concentrations (5 at % and more), there is an increase in
fluctuating magnetic field created around P by paramagnetic EuPO 4 nanoparticles. Similar
increase in the side band intensities and anisotropy values are also observed in 29 Si and
27 Al MAS NMR patterns of alumino silicates containing paramagnetic iron compounds [238,
239]. A schematic diagram showing the ion exchange process leading to the formation of Ga-
O-Eu linkages is shown in Fig.59. No separate peaks corresponding to EuPO 4 phase is seen
in the XRD patterns for sample corresponding to more than 2.5 atom % Eu 3+ . This is because
of its relatively smaller concentration and poor crystallinity associated with its nanophase
nature.
Table 6. The anisotropy parameter (∆δ) obtained form the components of the chemical shift
tensor (δ 11 , δ 22 and δ 33 ) which are calculated from the side band intensities
observed form the 31 P MAS NMR patterns of GaPO 4 sample containing different
amounts of Eu 3+ ions. The line width of the peak (Γ) is also given in the table. Error
in the chemical shift values is ±1 ppm.
Structural Value Value Value Value Value Value of ∆δ
Configuration of 31 P of δiso of Γ of δ11 of δ22 of δ33
(ppm)
(ppm) (Hz) (ppm) (ppm) (ppm) |δ 33 -δ 11 |
GaPO -10 344 2 -14 -18 20
4
GaPO4
-10.3 472 7 -17 -20 27
3+
with 2.5 at % Eu
GaPO 4
3+
with 5 at % Eu -10.3 516 21 -23 -29 50
GaPO 4
3+
with 10 at % Eu -10.3 626 29 -24 -36 65
111