过渡金属d能级诱导的可见光全波段可调宽谱敏化Yb3+ 1 μm发光材料的研究

As the luminescent centers in Luminescent Solar Concentrator (LSC), Yb3+ ions hardly absorb the visible part (380~760 nm) of solar spectrum. Recently, the tunable broadband sensitization absorption wavelengths are mostly confined to 250~500 nm. In order to fulfill sensitization of Yb3+ 1 μm emissions in the whole visible spectral range, we investigate two types of tunable broadband sensitizations based on the interaction between transition metal (TM) d levels and host lattice. Meanwhile, the relative physical models are set up in this project. According to different mechanisms, the two kinds of sensitization ways are ascribed to TM d-d intra-configuration broadband transitions and d-level induced host broadband absorptions, respectively. (1) For insulator host, the wavelengths and intensities of d-d transitions in visible range can be tailored through changing the crystal environment around TM ions; (2) For semiconductor host, Band-anticrossing (BAC) effect induced by TM d levels is used to tailor the wavelengths of host optical absorptions in visible range. Sequentially, the tunable broadband sensitizations of Yb3+ 1 μm emissions in the whole visible range can be achieved through energy transfer processes. This research helps to get a good understanding of the interactions between TM d levels and host lattice, and opens a perspective to design highly efficient inorganic photoluminescence materials for LSC.

作为太阳能荧光聚光器（LSC）的发光中心，Yb3+对于太阳光谱的可见波段（380~760 nm）几乎无吸收。目前的宽谱敏化体系可调控的吸收范围主要局限在250~500 nm。为了实现可见光全波段敏化Yb3+ 1 μm的发光，本项目基于过渡金属d能级与基质之间的相互作用探索两种可调宽谱敏化途径并建立物理模型。根据不同的作用机制，这两种敏化途径分别来自过渡金属d-d跃迁的宽谱吸收和d能级诱导的基质宽谱吸收。（1）对于绝缘体基质，通过晶体场环境的改变调控过渡金属d-d跃迁在可见波段的范围和强度；（2）对于半导体基质，利用过渡金属d能级诱导的Band-anticrossing (BAC)效应调控基质可见光波段的吸收峰范围。上述两种宽谱吸收与Yb3+通过能量传递可实现可见光全波段可调的宽谱敏化。本研究有助于深入理解过渡金属d能级与基质之间的作用关系，为设计高效的LSC无机荧光材料提供了参考思路。

本项目主要以过渡金属离子d能级的掺杂作为调控机制，实现对于Yb3+或其他近红外波段的稀土离子的目标近红外发光在几乎覆盖可见光波段的宽谱敏化。研究的体系主要集中在：（1）在绝缘体基质（La3Ga5.5Nb0.5O14）中，基于Cr3+在La3Ga5.5Nb0.5O14基质中同时占据四面体Ga格位(I)和八面体Ga格位（II），我们通过不同格位的占据调控Cr3+的d能级的宽谱吸收，探究了Cr(I), Cr(II)与Yb3+/Er3+之间的能量传递过程。结果证实Cr(II)作为主要敏化剂在400 ~ 800 nm范围内有效敏化Yb3+ 1.0 µm 和Er3+ 1.5 µm的发光，同时Cr(I)能量传递给Cr(II)从而影响Cr(II)的寿命衰减；（2）在半导体基质（CdO）中，通过V的掺杂引入的局域化d能级与基质导带发生Band anticrossing (BAC)耦合作用，探究V对于CdO基质的能带调控，实现了CdO吸收带在2.5 eV ~ 4 eV范围内连续可调。另外，研究还在已有体系（CdO, CaCuSi4O10）中探索了纳米合成步骤，积累了关于粒度分布与形貌特征之间关系的经验。本项目的研究为制备适用于LSC的高效无机荧光染料提供了理论和实验支持。