Intense Ultraviolet Photoluminescence Observed at Room Temperature from NiO Nano-porous Thin Films Grown by the Hydrothermal Technique

ABSTRACT We have successfully formed high-quality nanoporous NiO films by the hydrothermal technique and observed intense ultraviolet (UV) luminescence at room temperature. The SEM image reveals nanoporous NiO films with pore diameters from 70 to 500 nm. The results of XRD, Micro Raman and FTIR characterizations confirm the cubic structure of NiO. The optical band gaps estimated from the absorption spectrum are found to be 3.86 and 4.51 eV. The former is similar to that of bulk NiO, while the latter is much higher than that of bulk NiO. The increased band gap was attributed to the quantum confinement in the NiO nanocrystals, which may be present in the nanoporous NiO film. The room-temperature photoluminescence (PL) spectrum shows a peak of intense luminescence at 3.70 eV and several other peaks in the UV and near-UVwavelength regions. The intense UV luminescence at 3.70 eV was associated with the near band-edge emission and the others with defect-related emission. The high-quality wall of nanoporous NiO with a large surface-to-volume ratio provided the intense UV emission.