CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

water content in the reaction medium. Similar red shift is also observed in the excitation
spectrum with increase in water content.
Normalised Intensity
1. 0
0.8
0.6
0.4
0.2
0.0
(a)
35 ml H 2 O
15 ml H 2 O + 20 ml EG
10 ml H 2 O + 25 ml EG
5 ml H 2 O + 30 ml EG
35 ml EG
350 400 450 500 550 600
Wavelength (nm)
Normalised intensity
1.0
0.8
0.6
0.4
0.2
0.0
200 250 300 350
Wavelength (nm)
(b)
35 ml EG
30 ml EG+5 ml H 2
O
25 ml EG+10 ml H 2
O
20 ml EG+15 ml H 2
O
35 ml H 2
O
Fig.92.(a) Emission spectra of ZnGa 2 O 4 nanoparticle prepared in solvents containing
different ratios of EG and H 2 O. Corresponding excitation spectra are shown in Fig.92
(b)
Based on the previous studies, emission in the region of 385 to 455 nm has been
attributed to the de-excitation of energy levels characteristic of GaO 6 motif present in the
ZnGa 2 O 4 lattice [255]. The peak observed over the region of 250-290 nm in the excitation
spectrum has been attributed to the excitation of electrons from valence band to the
conduction band of ZnGa 2 O 4 lattice. As particle size decreases, energy values corresponding
to GaO 6 units also increases and this will lead to shifting of emission maxima towards lower
wavelength values. The same trend has also been observed in the excitation spectra, i.e.,
excitation maxima shifted from 250 to 275 nm with increase in particle size (Fig.92 (b)). The
excitation spectra also show a weak band which shifts from 310 to 345 nm with increase in
the particle size. This peak has been attributed to the localised levels corresponding to GaO 6
units in the band gap of ZnGa 2 O 4 lattice. Excitation of ZnGa 2 O 4 around 260 nm leads to
creation of charge carriers namely electrons in conduction band and holes in valance band.
The electron gets de-excited and reaches the localised levels created by the GaO 6 structural
153