CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

With increasing Tb 3+ ion concentration up to 2.5 atom%, the green emission (peak at 545 nm)
intensity increases and above that concentration it started decreasing. The decrease in
emission intensity beyond 2.5 at % is attributed to concentration quenching. Fig.86 (b) shows
the decay curves corresponding to 5 D 4 level of Tb 3+ from BiPO :Tb 3+
4 nanorods. All the
samples showed bi-exponential decay and the lifetime values are given in the Table 10.
Optimum lifetime values are obtained for 2.5 at % Tb 3+ doped BiPO nanorods.
4
Table 10. Lifetime values of 5 D 4 level of Tb 3+ from BiPO4 nanorods doped with different
amounts of Tb 3+ ion.
% of Tb 3+ 5 D 4 lifetime values of Tb 3+
τ 1 (ms) τ 2 (ms)
1 atom % 0.24 (13 %) 2.23 (87 %)
2.5 atom % 0.32 (11%) 2.62 (89%)
5 atom % 0.36 (15 %) 2.44 (85%)
4.4.6 Energy transfer from Tb 3+ to Eu 3+ ions in Tb 3+ co-doped BiPO 4 :Eu 3+ nanorods:
Figure 87 (a) shows the emission spectra of BiPO 4 :Eu 3+ (5 at %) and 5 at % Tb 3+ co-doped
BiPO 4 :Eu 3+ (5 at %) nanorods obtained after excitation at 255 nm. It is observed that Tb 3+
emission intensity decreases after co-doping with Eu 3+ . This indicates that energy transfer
takes place from Tb 3+ to Eu 3+ ions in the co-doped samples. Fig.87 (b) shows the excitation
spectra corresponding to Eu 3+ emission from both Eu 3+ single doped and Tb 3+ co-doped
BiPO 4 :Eu 3+ nanorods. Excitation spectrum corresponding to Eu 3+ emission from co-doped
sample showed peaks characteristic of both Eu-O charge transfer and 4f-5d transitions of
Tb 3+ . Unlike this the excitation spectrum corresponding to Tb 3+ emission at 545 nm from the
sample showed only 4f-5d transition of Tb 3+ . These results confirm that energy transfer takes
place from Tb 3+
to Eu 3+ . This is also understandable by considering the energy values
corresponding to 4f-5d transition of Tb 3+ and Eu-O charge transfer transition of Eu 3+ . Figure
87 (c) shows the decay curve corresponding to 5 D 4 level of Tb 3+ in the presence and absence
of Eu 3+ ion. It is observed that lifetime of Tb 3+ ions decreases after doping with Eu 3+ ions. On
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