5:15 PM - 5:30 PM
[20p-E302-14] Observation of down-conversion behavior in ZnO:Tm,Yb/ZnO core-shell nanowires
Keywords:Rare-earth-doped semiconductors, nanowire, downconversion
Down-conversion (DC) is a promising approach to improve the energy conversion efficiency of photovoltaics by absorbing one high-energy photon and emitting two lower-energy photons, which might overcome the theoretical upper limit of conversion efficiency of Si solar cells from 30 to ~40%. Tm,Yb-codoped ZnO (ZnO:Tm,Yb) is one of the most promising materials to improve the energy conversion efficiency of Si photovoltaics, where the ZnO host can absorb wide bandwidth of UV to violet light with large excitation cross section and transfer its energy to the rare-earth (RE) intra-4f shell, which yields light emission in the near-infrared regime from RE ions. Although we have been so far pursuing the growth of Tm,Yb-codoped ZnO films and observed characteristic light emission due to the intra-4f shell transitions of Tm3+ and Yb3+ ions, it has been difficult to obtain the highest 1G4-3H6 transition in the Tm3+ ions, corresponding to 489 nm emission, which is essential for the DC process. This is due to comparatively low crystal quality of ZnO films induced by a lattice mismatch between ZnO films and a sapphire substrate. In order to overcome this problem, we have introduced the nanowire (NW) architecture to improve the crystal quality of ZnO, and demonstrated the observation of the light emission at 489 nm originating from the intra 1G4-3H6 transition by growing ZnO:Tm,Yb/ZnO core-shell NW structures. In this contribution, we report the time-resolved photoluminescence (TR-PL) characteristics of Tm,Yb-codoped ZnO core/shell NWs to elucidate the energy transfer mechanism between each RE ions in the ZnO NWs which is essential for the DC process. The lifetime of each ion can vary by changing the concentration ratio of RE ions in the ZnO NWs, suggesting the controllability of the energy transfer between each RE ion in the ZnO NWs.