CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

3+
4.4.4 Luminescence studies on Eu doped BiPO 4 nanomaterials: Figure 85 (a) shows the
emission spectra of 1, 2, 2.5 and 5 atom% Eu doped BiPO 4 nanorods excited at 275 nm.
Strong orange and red emission is observed from the sample. The 590, 612, 650 and 700 nm
peaks are due to 5 D 0 → 7 F 5
1 , D 0 → 7 F 5
2 , D 0 → 7 F 3 and 5 D 0 → 7 F 3+
4 transitions of Eu , respectively.
The fine structure observed in the emission peaks shows the crystalline nature of host lattice.
As the concentration of Eu 3+ increases, the emission intensity initially increases up to 2.5
atom % and then decreases. Initially with increase in doping concentration, the number of
luminescent centers increases and as a result, emission intensity increases. However, above
certain doping concentration there is non-radiative decay due to energy transfer (migration)
among different Eu 3+ ions until it reaches a quenching centre. As a result, emission intensity
decreases. These results are further supported by the decay curve corresponding to the 5 D 0
level of Eu 3+ in these samples.
Intensity (arb.units)
400
300
200
100
λ exc
= 275 nm
1 % Eu
2 % Eu
2.5 % Eu
5 % Eu
Normalised intensity
1
0.1
0.01
λ exc
=275 nm & λ em
=615 nm
1% EU
2.5% Eu
5% Eu
0
550 600 650 700
Wavelength (nm)
(a)
0 2 4 6
Time (ms)
(b)
8
Fig.85. (a) Emission spectra obtained after excitation at 275 nm, (b) decay curves
corresponding to 5 D 0 level of Eu 3+ from BiPO 4 :Eu 3+ nanomaterials containing
different amounts of Eu 3+ .
The decay curves corresponding to 5 D level of Eu 3+
0 from these samples are shown in
Fig.85 (b) and their corresponding lifetime values are given in Table 9. All these curves are
bi-exponential in nature and based on the explanation given in the previous chapters, the
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