Study of excitonic UV emission stability, green luminescence and bandgap tune-ability in wurtzite (ZnO)1−x (Cr2O3)x composite

• Structural and optical analysis was made.
• Quenching phenomenon of green emission.
• Bandgaps modulation with Cr.
• The emissions were explained by effective-mass approximation.
• Different favorable luminescence mechanisms were explained explicitly.

In this research article deep level green luminescence quenching, stability of ultraviolet excitonic emission and structural properties of composite (ZnO)1−x (Cr2O3)x (x = 0, 5, 10 and 15 mol%) are investigated. X-ray diffraction has demonstrated polycrystalline wurtzite structured ZnO and established proper incorporation of Cr3+ 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% Cr2O3; however for 15 mol% Cr2O3, 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 (Eg) 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.