Kim Suhyeon, Yoon Sangho, Ahn Hyobin, Jin Gangtae, Kim Hyesun, Jo Moon-Ho, Lee Changgu, Kim Jonghwan, Ryu Sunmin
Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang 37673, Korea.
Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Korea.
ACS Nano. 2022 Oct 25;16(10):16385-16393. doi: 10.1021/acsnano.2c05600. Epub 2022 Sep 21.
Ultrathin layered crystals of coordinated chromium(III) are promising not only as two-dimensional (2D) magnets but also as 2D near-infrared (NIR) emitters due to long-range spin correlation and efficient transition between high- and low-spin excited states of Cr ions. In this study, we report on the dual-band NIR photoluminescence (PL) of CrPS and show that its excitonic emission bifurcates into fluorescence and phosphorescence depending on thickness, temperature, and defect density. In addition to the spectral branching, the biexponential decay of PL transients, also affected by the three factors, could be well described within a three-level kinetic model for Cr(III). In essence, the PL bifurcations are governed by activated reverse intersystem crossing from the low- to high-spin states, and the transition barrier becomes lower for thinner 2D samples because of surface-localized defects. Our findings can be generalized to 2D solids of coordinated metals and will be valuable in realizing groundbreaking magneto-optic functions and devices.
配位铬（III）的超薄层状晶体不仅有望成为二维（2D）磁体，还因其长程自旋相关性以及Cr离子高、低自旋激发态之间的有效跃迁而有望成为二维近红外（NIR）发射体。在本研究中，我们报道了CrPS的双波段近红外光致发光（PL），并表明其激子发射根据厚度、温度和缺陷密度分为荧光和磷光。除了光谱分支外，受这三个因素影响的PL瞬态的双指数衰减可以在Cr（III）的三能级动力学模型中得到很好的描述。本质上，PL分支由从低自旋态到高自旋态的激活反向系间窜越控制，由于表面局部缺陷，对于更薄的二维样品，跃迁势垒会变得更低。我们的发现可以推广到配位金属的二维固体，并且对于实现开创性的磁光功能和器件具有重要价值。
