CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

vibration of the Sb 4 O 6 ring is decomposed into 2A 1 + 2E + 2T 1 + 4T 2 of which A 1 , E and T 2
are Raman active modes. These modes are further classified into Sb–O–Sb stretch, Sb–O–Sb
bend and Sb–O–Sb wag modes [210]. The most affected modes in the nanorods (compared to
bulk Sb 2 O 3 ) are the Sb–O–Sb stretching (A 1 type) appearing at ~256 cm -1 and the Sb–O–Sb
bending (A 1 type) appearing at ~ 445 cm -1 . Another peak at ~ 710 cm -1 , also corresponds to
Sb–O–Sb stretching with T 2 symmetry. As reported above, the shape selective nature of the
nanorods results in only few of the modes that are affected, rest being unaltered. In
comparison to the bulk material, the oriented Sb 2 O 3 nanorods are expected to have Raman
activity in terms of the dynamic polarizability tensor. The A 1 type of vibrations include
polarizability of the kind α xx + α yy + α zz , while T 2 type of vibrations includes the non-diagonal
components like α xy , α yz , α zx [211]. Thus, the arrangement of the Sb 4 O 6 molecular units in
Sb 2 O 3 nanorods is associated with the selective excitation of some of these polarizability
tensors over the others, leading to enhanced Raman activity for a particular peak over the
other. This results in appearance of additional peak at ~ 256 cm -1 and a triplet at ~ 445 cm -1
for oriented samples. The A 1 type of modes have highest Raman activity (16 Å 4 amu -1 ) as
compared to E, T 1 and T 2 type [210]. Moreover, these shape selective changes in the dynamic
polarizability tensor is further regained to its bulk value (or at least tries to regain) by
annealing the nanorods at 100 and 200°C. Thus, the Raman and XRD investigations suggest
a clear morphological change in the Sb 2 O 3 , from nanorods to bulk particles. The structural
changes associated with morphological change are responsible for the change in
luminescence properties.
In the following section brief description regarding the interaction of these
luminescent nanorods with lanthanide ions are discussed. Eu 3+ ions are used as representative
lanthanide ions in the present study as its luminescence properties with respect to different
environments are well understood.
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