CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

nanocrystals is shown in Fig.10 [58]. The spectrum is characterised by mainly two peaks, one
sharp peak around 382 nm and other broad peak around 500 nm. The sharp peak has been
attributed to the band edge emission and the broad peak to the recombination of electrons
trapped at the oxygen defect levels and holes in the valance band of ZnO. It is observed that
the emission maximum is shifted in the visible regions depending on the synthesis conditions
and annealing temperatures [57].
Normalised Intensity
1.0
0.8
0.6
0.4
0.2
0.0
Band edge
emission
λ exc
= 325 nm
Defect emission
400 450 500 550 600
wavelength (nm)
Fig.10. Representative emission spectrum from ZnO nanocrystals obtained after excitation at
325 nm [58].
BaSnO 3 belongs to the family of cubic perovskite structure and exhibit interesting
optical and electrical properties. Mizoguchi, et al. [59] observed emission around 590 nm
from BaSnO 3 powder samples at low temperatures with corresponding excited state lifetime
of ~ 10μs. These authors have also observed emission in the near-infrared region form these
samples. SnO 2 is a direct band gap n-type semiconductor (E g = 3.6 eV). It is extensively used
for making sensors and optical devices [60-62]. Many authors have reported synthesis of
luminescent SnO 2 nanoparticles. For example, Gu, et al. [63] have reported the preparation of
SnO 2 nanoparticles by sol-gel method using SnCl 4·5H 2 O and NH 4 OH followed by heating
over the temperature range of 400 - 600°C. These particles showed luminescence around 400
nm characteristic of oxygen vacancies present in the nanoparticles and its intensity decreased
on increasing heat treatment temperature.
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