MacKeen C, Bridges F, Kozina M, Mehta A, Reid M F, Wells J-P R, Barandiarán Z
Physics Department, University of California , Santa Cruz, California 95064, United States.
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
J Phys Chem Lett. 2017 Jul 20;8(14):3313-3316. doi: 10.1021/acs.jpclett.7b01103. Epub 2017 Jul 7.
Yb-substituted CaF exhibits an anomalous red-shifted luminescence after UV excitation, attributed to the relaxation of impurity trapped excitons (ITE). CaF:Yb is the archetype system for this model, in which the Yb ions can be excited into a long-lived (ms) exciton state. Upon de-excitation, the emission intensity should be proportional to the Yb concentration, but that could not be checked when this model was first proposed. Using the X-ray absorption near edge structure (XANES) technique, we determine the fractions of Yb and Yb for low Yb concentrations, 0.01% to 0.1%, and thus determine the net concentration of Yb. A comparison with luminescence data shows that the intensity is not proportional to the Yb concentration, and only a fraction of Yb ions contributes to the anomalous luminescence. This is inconsistent with the ITE model and illustrates the importance of checking the dependence of the emission intensity on the Yb concentration.
镱（Yb）取代的CaF在紫外激发后呈现出异常的红移发光，这归因于杂质捕获激子（ITE）的弛豫。CaF:Yb是该模型的典型体系，其中Yb离子可被激发到长寿命（毫秒级）的激子态。在去激发时，发射强度应与Yb浓度成正比，但在该模型首次提出时无法对此进行验证。利用X射线吸收近边结构（XANES）技术，我们确定了低Yb浓度（0.01%至0.1%）下Yb和Yb的比例，从而确定了Yb的净浓度。与发光数据的比较表明，强度与Yb浓度不成正比，只有一部分Yb离子对异常发光有贡献。这与ITE模型不一致，并说明了检验发射强度对Yb浓度依赖性的重要性。
