Excitation transfer in zirconia nanocrystals and ceramics
|Donats Millers 1, Larisa Grigorjeva 1, Krisjanis Smits 1, Janusz D. Fidelus 2, Agnieszka Opalińska 2,3, Witold Łojkowski 2|
1. Institute of Solid State Physics, University of Latvia, 8 Kengaraga, Riga LV-1063, Latvia
The electronic excitations (charge carriers, excitons) in zirconia are mobile at room temperature. Therefore the energy and/or charge transfer take place and final stages of these processes are either the excitation trapping at crystalline lattice imperfections, either the self-trapping (excitation self-localization in the initially perfect lattice). The both cases could result in creation of excited state and this excited state is origin of luminescence. Hence, the study of time – resolved luminescence provide information of excitation transfer processes. The pure and rare earth doped zirconia nanocrystals as well as ceramics were studied by time resolved luminescence methods under 3 kinds of excitation: nitrogen laser (337 nm) pulses, YAG:Nd laser (532 nm and 266 nm) second and forth harmonic pulses, electron beam (270 kV, 1012 el/cm2 per pulse) pulses. The laser beam excitation is within band gap and therefore lattice defects and dopands were excited. Electron beam excitation creates the electrons and holes mainly in host lattice. The defects concentration in oxygen sub-lattice was changed via zirconia annealing at different oxygen partial pressure. The increase of defects concentration in oxygen sub-lattice causes the increase of luminescence intensity under excitation within band gap region, whereas the intensity of luminescence was suppressed if band carriers were created. It is suggested the defects in oxygen sub-lattice acts as efficient traps for charge carriers, but they are not a radiative recombination centers. The processes were similar in free-standing nanocrystals and nanostructured ceramics. The dopands introduced allowed to study the electronic excitation trasfer process from host to the dopand via comparision of result of dopand direct excitation with that of host band-to-band excitation.
The work was partly supported by grants 05.1720 of LCS and no. N N508 0851 33 of MNiSW granted for the years 2007 – 2009
Presentation: Poster at E-MRS Fall Meeting 2008, Symposium I, by Donats Millers
See On-line Journal of E-MRS Fall Meeting 2008
Submitted: 2008-05-19 13:43 Revised: 2008-05-28 16:07