CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

The luminescence dynamics associated with multiple lifetime components can be better
pictured through effective lifetime (τ eff ). The effective lifetime (τ eff ), which is measure of the
average environment around the Tb 3+ ions in the sample, is calculated based on the equation
(20).
τ
eff
=
∞
∫
0
∞
∫
0
tI () t dt
I()
t dt
………………… (20)
From Table 8 it is evident that, Ce
where I(t) is the intensity at any time t
3+ 3+
co-doping in SbPO 4 :Tb , leads to slight increase in the
τ 2 component of the decay corresponding to the 5 D level of Tb 3+ ions. This increase in the τ
4 2
component is responsible for the increased τ eff values. The bi-exponential nature of the decay
3+ 3+
curves of SbPO 4 :Tb (5%) and SbPO 4 :Ce (2.5%),Tb 3+ (5%) nanoribbons/ nanoparticles can
be attributed to the presence of Tb 3+ ions in at least in two different environments, namely the
one at the bulk and the other at the surface of the nanoribbons/ nanoparticles. The
luminescence originating from the surface of the nanoribbons/ nanoparticles is responsible
for the τ 1 component whereas that originating from the bulk is responsible for τ2 component.
The lanthanide ions at the surface will undergo faster quenching compared to the ones at the
bulk due to the presence of stabilising ligands at the surface. The vibrations associated with
the C-H, O-H and C-O linkages of the stabilising ligands are responsible for the non-radiative
decay of the lanthanide ions excited states. The presence of stabilising ligand with the SbPO 4
nanoribbons/ nanoparticles has been confirmed from IR pattern of the sample. Thus an
increased component of the non-radiative transition in case of samples which are not
incorporated in silica, results in a shorter lifetime component. However, when the
nanoribbons/ nanoparticles are dispersed in silica, the ligands are removed from the surface,
thereby leading to the appearance of a single exponential decay curve. The similar τ values 1
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