ZnO microtubes: formation mechanism and whispering-gallery mode lasing

The luminescent and laser properties of ZnO microtubes synthesized by a modified thermal evaporation method were studied using photoluminescence spectroscopy. It was shown that whispering gallery modes are responsible for lasing in the near UV range. The possibility of achieving low lasing thresholds (down to ~ 8 kW/cm2) and high optical quality factors (over 3900) was demonstrated. A mechanism for the formation of such microcrystals was proposed, based on the assumption of simultaneous growth and etching along the [0001] crystallographic direction.