CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...
CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...
CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...
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CHAPTER 5: Zinc gallate (ZnGa 2 O 4 )<br />
5.1. Introduction: Zinc gallate (ZnGa 2 O 4 ) belongs to the class of inorganic compounds<br />
having spinel structure. It crystallises in cubic structure with a space group of Fd3m [247].<br />
ZnGa 2 O 4 is an insulator with a band gap of 4.4 eV and has potential applications as materials<br />
for low voltage field emission displays (FEDs), electro-luminescent devices (ELDs) and<br />
vacuum fluorescent displays (VFDs) [247-254]. ZnGa 2 O 4 exhibits higher chemical stability<br />
under high electric field and strong electron bombardment when compared with conventional<br />
sulfide based phosphors [251, 254]. Blue emission has been observed from ZnGa 2 O 4 and is<br />
due to a transition via a self-activation centre under UV or low voltage electron excitations<br />
[255]. The intensity and wavelength maximum corresponding to blue emission vary with the<br />
nature of dopants. For example detailed studies are available regarding the luminescent<br />
properties of ZnGa 2 O 4 when partially substituted with metal ions like Cd 2+ (for Zn 2+ ) and<br />
In 3+ (for Ga 3+ ) [ 256-258]. If nanoparticles of such luminescent materials are prepared with<br />
sufficient dispersability in organic solvents, then polymer based luminescent materials can be<br />
made out of them. Polymer based materials can be converted into devices by using cheap<br />
fabrication techniques. Primary requirement for incorporating nanoparticles in polymer<br />
matrix is to make them highly dispersible in organic solvents by stabilizing the nanoparticles<br />
with bulky organic ligands. However, such ligand-stabilised nanoparticles can be obtained<br />
only when the synthesis temperature is less than 250°C, so that as to prevent decomposition<br />
coordinated ligand. Hirano, et al. prepared ZnGa 2 O 4 nanoparticles at a relatively low<br />
temperature of 90°C from aqueous solution of ZnSO 4 and Ga 2 (SO 4 ) 3 by using precipitating<br />
agents like urea, aqueous ammonia and hexamethyl tetramine [248]. However, in this method<br />
ligand stabilization is difficult, as H 2 O being a solvent with low viscosity and poor<br />
coordinating characteristics does not prevent aggregation of the nanoparticles. Many methods<br />
are reported for the synthesis of ZnGa 2 O 4 nanomaterials in the form of nanowires, helical<br />
149