Research On Host Sensitized Near Infrared Downconversion Luminescence Of Vanadate Materials

Rare earth doped luminescent materials could act as spectral converters to reduce the spectral losses and enhance the conversion efficiency in silicon-based photovoltaic devices. In this work, the self-activited vanadates with excellent chemical and thermal stability were chosen as host lattice. By doping with Yb³⁺/Nd³⁺ ions, we developed some near infrared （NIR） phosphors with broadband absorption, and further discussed their structures, luminescent properties as well as luminescent mechanism.NaMg₂Ca₂V₃O₁₂ powders were synthesized by a sol-gel method, and these samples show intense broad excitation spectra in ultraviolet （UV,200-400 nm）. With Yb³⁺ doped, the light conversion from UV to NIR was realized, which provides the possibility for the application in solar cells. Impurity peaks of YbVO₄ appeared due to different valences and radii between Yb³⁺ and Ca²⁺ ions when the concentration of Yb³⁺ beyond 4%. Therefore, in order to obtain more efficient NIR emission, vanadates containing rare earth ions may be the better choice as host lattice.Na₂RMg₂V₃O₁₂ （R = Y, Gd） compounds were prepared by a sol-gel method. Comparing their luminescent properties and thermal stability, it is found that the sample Na₂GdMg₂V₃O₁₂ presents more excellent optical performance. The light conversion from UV to NIR was realized by single-doped Yb³⁺, while the excitation spectrum is extended from UV to visible （Vis） through solely doped Nd³⁺. The optimal concentration and concentration quenching mechanism were discussed in Yb³⁺ or Nd³⁺ single-doped Na₂RMg₂V₃O₁₂ samples. The occurrence of energy transfer （ET） from [VO₄]^3- to Yb³⁺ or Nd³⁺ is confirmed by the luminescent spectra and lifetimes, and results indicate that the energy transfer from [VO₄]^3- to Nd³⁺ is more efficient.The photoluminescence emission （PL） and excitation （PLE） spectra along with decay curves of Nd³⁺-Yb³⁺ co-doped Na₂GdMg₂V₃O₁₂ were also investigated, and four possible energy transfer processes are proposed:（a） [VO₄]^3-→Yb³⁺; （b） [VO₄]^3-→Nd³⁺; （c） Nd³⁺→ Yb³⁺; （d） [VO₄]^3-→Nd³⁺→Yb³⁺. By comparison, it is found that the co-doped system has the strongest NIR emission and could convert UV-Vis light into NIR at around 1000 nm, which matches well with the response curve of the silicon solar cell. Results indicate that the Nd³⁺-Yb³⁺ co-doped Na₂GdMg₂V₃O₁₂ samples are more efficient solar spectral convertors to enhance the conversion efficiency of the silicon solar cell in comparison with those of Nd³⁺ or Yb³⁺ solely doped systems.