Phase stability and oxygen-sensitive photoluminescence of ZrO2:Eu,Nb nanopowders.

We studied structure and oxygen-sensitive photoluminescence (PL) of ZrO 2 :Eu,Nb nanocrystalline powders synthesized via a sol-gel route and heat-treated up to 1200 °C. The material containing only 2 at% Eu 3+ was predominantly monoclinic, whereas 8 at% of Eu 3+ stabilized tetragonal phase. Comparable amount of niobium co-doping effectively suppressed the formation of tetragonal phase. PL of Eu 3+ ions was observed under direct excitation at 395 nm. PL decay kinetics showed that the luminescence was partially quenched, depending on doping concentrations and ambient atmosphere. At 300 °C, the PL intensity of all samples systematically responded (with up to 70% change) to changing oxygen content in the O 2 /N 2 mixture at atmospheric pressure. At low doping levels, the dominant factor controlling the PL intensity was an energy transfer from excited PL centers to randomly distributed defects in the ZrO 2 lattice. We argue that the charge transfer between the defects and adsorbed oxygen molecules alters the ability of the defects to quench Eu 3+ luminescence. At high doping levels, another type of sensor response was observed, where some Eu 3+ emitters are effectively switched on or off by the change of ambient gas. A remarkable feature of the studied material is a reversing of the sensor response with the variation of the Nb concentration. [ABSTRACT FROM AUTHOR]