CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

Room temperature and 100°C synthesized samples showed particles with size in the range of
50-80 nm and 70-100 nm, respectively. BiPO 4 samples prepared at 125 and 185°C shows rod
shaped morphology with lengths in the range ~ 450-750 and 1000-1200 nm with
corresponding widths ~ 50-120 and 100-170 nm, respectively. The SAED patterns show that
these nanomaterials are single crystalline in nature and their crystallinity increases with
increase in the reaction temperature. The possible reason for change in morphology with
increase in temperature is the increasing concentration of nuclei and associated anisotropic
growth brought about by the reaction temperature.
3+
4.4.2 Effect of particle size and crystal structure on Eu emission from BiPO 4 :Eu 3+
nanomaterials: Figure 80 (a) shows the emission spectra of Eu 3+ doped hydrated hexagonal
BiPO 4, anhydrous hexagonal BiPO 4, and monoclinic BiPO4 nanomaterials on 270 nm
excitation. The intensity of Eu 3+
luminescence increases with increase in the reaction
temperature. It has been attributed to the combined effect of improved crystallinity and
removal of water molecules present in the lattice. Water molecules quench the excited state
of Eu 3+ , thereby reducing its luminescence intensity. Europium ions in the BiPO 4 lattice show
four intense emission peaks at 590, 615, 650 and 700 nm and are due to 5 D Æ
7 F , 5 D
0 1 0
Æ
7 5 7 5 7 3+
F 2, D0 Æ F3 and D0 Æ F 4 transitions of Eu . Improved crystallinity of BiPO4 samples
with increase in temperature of synthesis is also clear from the fine structure of the emission
spectrum (Fig 80 (a)), particularly for the 185°C heated samples. The corresponding
excitation spectra monitored at 615 nm emission from the samples is shown in Fig.80 (b). It
shows broad intense band centered at 270 nm with a shoulder at 255 nm along with many
sharp peaks in the wavelength range of 310 - 420 nm. The broad band centered at 270 nm is
due to the Eu-O charge transfer process and the shoulder at 255 nm is due to host absorption.
Observation of host excitation peak while monitoring Eu 3+ emission from the sample confirm
that the energy transfer takes place from host to Eu 3+ ions. The sharp peaks in the wavelength
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