Gas-induced suppression of excitons formation in Zinc oxide

We investigate the effects exerted by nitrogen dioxide (NO2) exposure on excitonic photoluminescence efficiency and on excitons radiative lifetime in nano-structured versus micro-structured ZnO films synthesized by wet chemical routes. We show that the presence of the oxidant species unambiguously give rise to an increment of the energy barrier at ZnO surfaces, while at the same time it leaves unaffected the decay dynamics of free excitons. By comparing the results obtained for different kind of topologies, we deduce that the fundamental mechanism driving the NO2-induced photoluminescence quenching is the inhibition of free excitons formation.