Enhanced green luminescence from ZnO nanorods

Preferentially c-axis oriented ZnO nanorods were grown on a ZnO seed layer spin coated on a crystalline silicon substrate. A low-temperature aqueous chemical growth method using the chemical bath deposition technique was used to grow the ZnO nanorods. The samples were annealed at 700 °C in a reducing atmosphere (H ₂ /Ar) with a relative ratio of 5%:95% for different times (20, 30, and 50 min). X-ray diffraction analysis revealed that the crystallite sizes increased with an increasing annealing time up to 30 min and then decreased for longer annealing time. Scanning electron microscope images showed a successful growth of the vertically aligned ZnO nanorods which were approximately 500 nm in length and 50 nm in diameter. The diameter of the nanorods increased with an increasing annealing time up to 30 min and then decreased when the annealing time was increased further. Photoluminescence (PL) measurements confirmed that the unannealed sample exhibited two distinct emissions, namely, the band to band emission around 378 nm and a broad orange emission centered at 600 nm which was due to the oxygen related defects. The annealed samples exhibited only a broad green emission centered at 500 nm and their intensities increased with annealing time. The highest intensity was recorded for the sample annealed for 30 min and the intensity decreased for further annealing time. The deconvoluted PL peak of the green emission indicated that three different kinds of defects were responsible for the emission at 500 nm. The decay measurements indicated that the green emission (500 nm) had an average lifetime of 11.58 μs. The quantum yield of the sample annealed for 30 min was measured using an integrating sphere at a wavelength of 325 nm, and it was found to be 43%. These ZnO nanorods can be very useful in optoelectronic applications, such as green light emitting diodes and field emission displays.