Study of excitonic UV emission stability, green luminescence and bandgap tune-ability in wurtzite (ZnO)_(1-x) (Cr_2O_3)_x composite

摘要

In this research article deep level green luminescence quenching, stability of ultraviolet excitonic emission and structural properties of composite (ZnO)_(1-x_(Cr_2O_3)_x (x = 0, 5, 10 and 15 mol%) are investigated. X-ray diffraction has demonstrated polycrystalline wurtzite structured ZnO and established proper incorporation of Cr~(3+) at most likely on the Zn lattice sites. More likely, the crystallite size and lattice constants (c, a) decrease while consequently the dislocation density is increased. A pronounced excitonic UV emission due to band-band transition and a weak deep level green emission caused by the oxygen vacancies are observed at peak-wavelengths (358-370) nm and (536-538) nm respectively. The UV luminescence shows a blue-shift and well-built stability up-to 10 mol% Cr_2O_3; however for 15 mol% Cr_2O_3, both the UV and green emissions are completely suppressed while an orange emission appears at 640 nm. This emission is attributed to radiative recombination of a delocalized electron closed to the conduction band with deeply trapped hole in the oxygen interstitials (Oi- centers). Energy bandgap (E_g) is finely tuned from 3.35 eV to 3.46 eV. The exhibited blue shift in the energy bandgap is attributed to Burstein-Moss shift explained by the photon energy dependent measurements. The favorable assorted luminescence mechanisms are explained explicitly.