Down conversion of solar UV and blue light is one of the few ways of surpassing the Shockley-Queisser limit of solar cells. One of the most efficient down conversion systems is the Pr³⁺ - Yb³⁺ lanthanide pair. However, these ions do not provide any strong absorption for solar UV and blue light, thus require sensitizing. In this work, we report self-sensitization by inducing strong Laporte allowed f → d and charge transfer transitions on Pr³⁺ and Yb³⁺, respectively. By replacing oxygen or fluorine anions with the more polarizable and reducible S²⁻, the chemical bonds become more covalent, the d-shell of Pr³⁺ and the anion-to-Yb³⁺ charge transfer states are lowered into the near-UV and blue range. This avoids the need for a third strongly absorbing specie that may be difficult to include into the matrix or might provide other quenching routes by, for example, introducing new defects. The down conversion system can thus be kept simple, without more dopants types than the two lanthanides. The straightforward two-step synthesis of NaYS₂ is realized without toxic H₂S, and both precursor chemicals and produced material can be handled in air. The optical and chemical properties of NaYS₂, no need for an additional sensitizer and easy synthesis are strong arguments that the little explored NaYS₂-type materials deserves more attention.

向下转换太阳能紫外线和蓝光是超越太阳能电池的Shockley-Queisser极限的几种方法之一。最有效的下变频系统之一是Pr ³⁺ -Yb ³⁺镧系元素对。但是，这些离子不能为太阳紫外线和蓝光提供任何强吸收，因此需要敏化。在这项工作中，我们通过诱导强Laporte允许f→d以及分别在Pr ³⁺和Yb ³⁺上的电荷转移跃迁来报告自敏化。通过用更可极化和可还原的S ^2-取代氧或氟阴离子，化学键变得更共价，Pr ³⁺的d-壳和阴离子-Yb ³⁺电荷转移状态降低到近紫外线和蓝色范围。这避免了可能需要难以包含在基质中或可能通过例如引入新的缺陷而提供其他淬灭途径的第三种强吸收物质。因此，下变换系统可以保持简单，而没有比两种镧系元素更多的掺杂剂类型。NaYS ₂的直接两步合成无需毒性H ₂ S即可实现，并且前体化学品和产生的材料都可以在空气中处理。NaYS ₂的光学和化学性质，不需要额外的敏化剂和易于合成是有力的论据，即很少探索的NaYS ₂型材料值得更多关注。