X-ray luminescence of ZnO whisker microstructures

Morphology and the optical and luminescent properties of zinc oxide (ZnO) whisker microcrystal arrays grown on sapphire using gas-transport synthesis from zinc vapors in oxygen by vapor–liquid–solid (VLS) mechanism have been studied. The arrays consisted of uniaxial microcrystals with two morphologies, combining hexagonal prisms and single-crystalline microrods. Short-wavelength boundary of transparency of the whisker microcrystal arrays occurs in a region of 385–395 nm. Total transmission in the visible and near-IR spectral range is on a level of 10–20% for layer thicknesses about 15–18 $\mu$m. The X-ray luminescence spectrum displays two bands: (i) an intense narrow excitonic peak at 388.3 nm and (ii) an about 2.5 times less intense broad band in a region of 430–600 nm. The time constant of the decay of excitonic luminescence from undoped ZnO microstructures has been estimated for the first time at about 1.1 ns (with the exciting pulse width not taken into account).