CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

These inferences are further substantiated by decay curves corresponding to 5 D 0 level
of Eu 3+ (Fig.29 (a)) from these samples. The decay has been found to be single exponential
for all the samples with lifetime value around 340μs. The values are higher than that of
Europium hydroxide (250 μs) prepared by the identical method as that of GaOOH. Identical
lifetime values corresponding to the 5 D 4 level of Tb 3+ ions (1.2 ms (80%) and 388μs (20%))
are also observed for GaOOH samples containing different amounts of Tb 3+ (Fig.29 (b)).
Hence from the decay curves and emission spectra, it is inferred that lanthanide hydroxide
phase is finely mixed with amorphous gallium hydroxide and crystalline GaOOH phase.
These results are further supported by the thermo-gravimetry and differential thermal analysis
studies on the samples.
Normalised intensity
1
0.1
0.01
0.50 at % Eu 3+
0.75 at % Eu 3+
1.00 at % Eu 3+
3.00 at % Eu 3+
5.00 at % Eu 3+
Normalised intensity
1
0.1
0.01
0.5 at% Tb 3+
1 at% Tb 3+
1.5 at% Tb 3+
0 1 2
Time (ms)
(a)
3
0 2 4 6 8
(b)
Time (ms)
10
Fig.29. Decay curves corresponding to (a) 5 D 0 level of Eu 3+ ions (b) 5 D 4 level of Tb 3+ ions
from GaOOH samples prepared with different concentrations of Eu 3+ and Tb 3+ ions,
respectively. (λ exc = 270, 255 nm and λ em = 615, 545 nm for Eu 3+ and Tb 3+ doped
GaOOH, respectively)
Thermo gravimetric (TG) and differential thermal analysis (DTA) patterns of the
GaOOH sample prepared in the presence of different concentrations of Eu 3+ ions are shown
in Fig.30. GaOOH sample prepared in the absence of any Eu 3+ ions is characterised by two
stages of weight losses in its thermogram (Fig.30 (a)). They are in the range of 200-280°C
and 350-420°C and have been attributed to dehydration of surface bound hydroxyl groups
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