Positron-Annihilation, Structural and Optical Studies on Properties of Nanostructured $ZrO_2,$ $ZnO,$ $Bi_2O_3$ and $ZnO-Bi_2O_3$

Nanostructured oxides, like $ZrO_2,$ on $ZnO$ and $Bi_2O_3$ show interesting electronic and photovoltaic properties. Pressed and annealed samples were obtained from nanopowders grown in hydrothermal or plasma processes. Positron annihilation (the Doppler broadening depth-resolved, positron lifetime) techniques were used to trace structural changes in samples after annealing. Photoluminescence spectra of all investigated samples show broad-band emission in the visible, with intensity depending on annealing temperature. The change in nanoporosity and positron lifetimes correlate well with changes in photoluminescence properties. The nature of broad photoluminescence bands is to be understood; further positron studies via the Doppler coincidence method would help in identifying the nature of defects in these samples.