Broadband spectral conversion due to cooperative and phonon-assistant energy transfer from ZnO to Yb3+

Abstract

The broadband spectral conversion from near-UV absorption into near-infrared emission around 1 μm is reported in the ZnO–LiYbO2 hybrid phosphor, which is the benefit from the efficient energy transfer from ZnO to the Yb3+ ions that are specifically located at the interfacial diffusion regions between ZnO and LiYbO2, rather than those in LiYbO2 crystals. The Li+-related and Yb3+-related defect energy levels are formed inside the ZnO band gap in the ZnO–LiYbO2 hybrid phosphor; the former act as the quenching centers for the excitons in ZnO and meanwhile the efficient energy donors for Yb3+ ions, and the latter are responsible for the red shift of ZnO visible emission when the excitation energy is lower than E g. The excitation power dependence of Yb3+ emission intensities is measured to investigate the number of photons that are involved in the energy transfer process, which reveals that there are two channels for the sensitizing of Yb3+: One is due to the energy transfer by the recombination of electrons and holes, which is a cooperative energy transfer process, and the other is via the energy feeding from the Li+-related energy levels, which is a phonon-assistant energy transfer process.