Into the nature of Pd-dopant induced local phonon modes and associated disorders in ZnO; based on spatial correlation model

In this paper a comprehensive study has been conducted to investigate the effect of palladium dopant (Pd) on the interior disordered properties of ZnO in terms of spatial correlation-length (L). Spatial correlation model is employed to explicate and gets insight of the broadening and asymmetry of the first-order optical phonon mode induced by the do-pant potential fluctuation. Apart from the conventional phonon modes associated with w-ZnO, origin of the additional local modes associated with Pd and subsequently dopant induced blue-shift in the principle E2 (high) phonon mode has been assessed. The system so--investigated is a chemically prepared composite Zn1−xPdxO (with x = 0, 2, 4 and 6 at %) nanopowder. Photoluminescence shows a blue-shift in the UV emission as a consequence of the extension of energy band-gap. The structural analysis based on X-ray diffraction reveals the absence of Pd-related secondary phases in contradicts to Raman analysis suggests Raman as the most sensitive technique. Crystallite size (D), dislocation density (δ) and optical band-gap (Eg) so-determined are correlated to spatial correlation-length “L” to account for the observed properties in photo-catalytic applications.