CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

that are observed for both the SbPO 4 :Tb 3+ (5%) and SbPO 4 :Ce 3+ (2.5%),Tb 3+ (5%) samples
further support that the faster component (τ 1 ) is originating from the lanthanide ions present
at the surface of the nanoribbons/ nanoparticles. Replacement of the ligands from the surface
of the nanoparticles by silica matrix is schematically shown in Fig.74.
CH2
CH2 CH2
OH OH OH
CH CH 2 CH 2
OH OH
CH 2 CH 2
OH OH
SbPO 4
:Ln 3+
OH OH
CH 2 CH 2
CH CH2 2
OH OH
Incorporation
in SiO 2
CH 2 CH 2
OH OH
SiO 2
OH
OH
SbPO 4
:Ln 3+
OH OH
CH 2 CH 2
CH 2 CH 2
CH2 CH2
OH OH
Fig.74. Schematic representation showing the effect of incorporation of nanoparticles in silica
matrix.
In order to confirm whether energy transfer is taking place between Ce 3+ and Tb 3+
ions in the SbPO 4 :Ce 3+ , Tb 3+ nanoribbons/ nanoparticles, excitation spectra were recorded by
monitoring the 5 D 4 → 7 F 5 transition of Tb 3+ ions at 545 nm (Fig.75). The excitation spectrum
of SbPO 4 :Tb 3+ (5%) (Fig.75 (a)) has a broad and intense band at ~250 nm and sharp and weak
features at 284, 303, and 318 nm. The former broad band at ~250 nm corresponds to allowed
4f to 5d transition of Tb 3+ and latter sharp peaks belong to intra 4f transitions of Tb 3+ ion. The
lower intensity of latter peaks is because of forbidden nature of f-f transitions. The shielding
of 4f electrons by 5s and 5p electrons from surroundings results in the relatively sharper
peaks. Co-doping SbPO 4 :Tb 3+ (5%) nanoribbons/ nanoparticles with Ce 3+
results in an
additional peak centered around 278 nm with two shoulders. As 4f→5d transition of Tb 3+ and
Ce 3+ ions have very high value of oscillator strength and assuming comparable transition
probabilities for the 4f→5d transition of Tb 3+ and Ce 3+ ions, the excitation spectrum has been
de-convoluted based on a Gaussian fit. De-convolution of the excitation spectrum revealed
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