CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

found to be 0.97. A comparison of the emission spectrum shown in Fig.56 (b and c) suggests
that Eu
3+ 3+
ions exist as a separate EuPO 4 phase in 5 at % Eu containing sample. However,
for 2.5 at % Eu 3+ containing sample, the asymmetric ratio of luminescence is quite different
from EuPO
3+
phase, suggesting that Eu ions are in a different environment in GaPO
4 4
nanoparticles containing 2.5 at % Eu 3+ . Presence of Eu 3+ ions during precipitation reaction to
form GaPO 4 can either lead to the formation of europium hydroxide phase or result in
replacing protons of the surface hydroxyl groups attached to surface gallium or phosphorus
species present on the nanoparticles.
In order to check the first possibility, Eu 3+ ions were subjected to hydrolysis in
glycerol medium using urea as the reagent for hydroxide formation (urea and not ammonium
dihydrogen phosphate was used for precipitation to prevent the formation of EuPO 4 phase).
Emission spectrum from the sample obtained after 260 nm excitation is shown in Fig.57. The
asymmetric ratio of luminescence is found to be 4.2 which is significantly higher than the
3+
value 2.2 observed from GaPO4 nanoparticles containing 2.5 at % Eu ions. These data
suggest that Eu 3+ ions do not exist as europium hydroxide phase along with the GaPO 4
nanoparticles.
600
5 D 0
7 F 2
Intensity
400
200
5 D 0
7 F 1
5 D 0
7 F 4
0
500 550 600 650 700 750
Wavelength (nm)
Fig.57 Emission spectrum of europium hydroxide sample prepared in glycerol medium by the
identical method as that employed for GaPO 4 and EuPO4 nanoparticles, except that
urea rather than ammonium dihydrogen phosphate was used to create the alkaline
environment and to prevent the formation of EuPO 4 phase.
108