CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

900°C
Intensity (arb.units)
700°C
500°C
300°C
asprepared
10 20 30 40 50 60
2 θ/°
Fig.110. XRD patterns of as prepared, 300, 500, 700 and 900°C heated CaWO 4 nanoparticles.
Table 14. Average crystallite size of CaWO 4 nanoparticles as a function of heat treatment
temperatures.
Temperature (°C)
Avg. crystallite size (in nm)
As prepared (Room temperature) 7
300 8
500 26
700 90
900 99
6.6. Effect of particle size on photoluminescence of CaWO 4 nanoparticles: Emission
spectra of CaWO 4 nanoparticles heated at different temperatures obtained after excitation at
253 nm is shown in Fig.111 (a). As prepared (particle size 7 nm) and 300°C heated (particle
size 8 nm) samples show weak emission and are having almost same intensity. Unlike this
samples heated at 700°C (particle size 90 nm) and 900°C (particle size 99 nm) show bright
luminescence and their intensities are almost same. Luminescence of 500°C (26 nm) heated
samples is slightly higher than 300°C heated sample, but much lower than 700°C heated
sample. Based on these results, it is inferred that photoluminescence of CaWO 4 nanoparticles
increases with increase in the particle size and crystallinity and associated decrease in the
concentration of surface quenching sites.
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