CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

700
Intensity (arb.units)
600
λ exc
= 253 nm
500
400
300
200
100
0
350 400 450 500 550 600 650
Wavelength (nm)
(a)
(b)
1.0
Normalised Intensity
0.8
0.6
0.4
0.2
λ em
= 425 nm
Intensity (arb.units)
100
10
λ exc
= 253 nm & λ em
= 425 nm
0.0
0 5 10 15 20 25
200 250 300 350 400
Time (μs)
Wavelength (nm)
(c)
(d)
Fig.109. Emission spectrum (a) and photograph of emission (b) obtained from CaWO 4 :Eu
nanoparticles after excitation at 253 nm. The corresponding excitation spectrum and
decay curve, both monitored at 425 nm emission are shown in Fig.109 (c) and (d)
respectively.
6.5. Effect of heat treatment on particle size: CaWO 4 nanoparticles prepared at room
temperature were heated at different temperatures ranging from 300 to 900°C in air for 8
hours and their XRD patterns are shown in Fig.110. All the samples show characteristic
peaks of scheelite structure with tetragonal unit cell. With increase in the heating
temperature, XRD peaks become sharper. This is due to the increase in the average crystallite
size on aggregation. Average crystallite size has been calculated by using Debye-Scherrer
formula (Table 14) and found to increase from 7 to 99 nm as temperature increases from
room temperature to 900°C.
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