Wavelength conversion characteristics of Eu3+/Yb3+-activated La2O2S luminophor

We have fabricated a La2O2S luminophor doped with Eu3+ and/or Yb3+ via a solid state reaction process, and measured radiative emissions in the visible and near-infrared wavelengths under excitation at ultraviolet wavelengths. In particular, the wavelength conversion characteristics of this oxysulfide matrix were investigated in comparison with a La2O3 + La(OH)3 matrix. The rare earth ions embedded in the oxysulfide matrix feel crystal fields with poorer inversion symmetry relative to those in the oxide counterpart. This is attributed to the coexistence of oxygen and sulfur ions in their first coordination shells. Consequently, the La2O2S luminophor provides better performance in terms of emission intensity and spontaneous emission rate. In addition, under excitation at ultraviolet wavelengths, the Eu3+/Yb3+-doped La2O2S powders exhibited many strong emissions at wavelengths that can be efficiently absorbed by a typical Si-based solar cell.