Defect Engineering of Spin-Correlated Luminescent Dopants in Ferromagnetic van der Waals Materials

Abstract

The controlled introduction of impurities into crystals provides a powerful means of tailoring material properties and imparting new functionalities not inherent to the native lattice. Recently, magnetically ordered van der Waals (vdW) materials have emerged as a leading platform for next-generation two-dimensional (2D) spin-based electronics, however, deliberate incorporation of optical impurities in these materials remains largely untapped. This dissertation presents the use of spin-bearing Yb3+ as a substitutional point defect in the archetypical vdW magnet CrX3, marking the first report of any extrinsic dopant serving as an optically active point defect across all magnetically ordered vdW compounds. This work demonstrates the transformation of the featureless broadband d-d photoluminescence (PL) of the CrX3 host lattice into narrow-line, spin- polarized f-f emission originating from isolated Yb3+ impurity centers, without any degradation of the host lattice magnetic integrity. Via strong superexchange coupling, the Yb3+ magnetization is pinned to the host CrX3 magnetization, allowing for the controllable spin manipulation of the paramagnetic Yb3+ impurities by the lattice. This work highlights the use of Yb3+ as an optical probe to investigate local spin correlations and excited-state dynamics, emphasizing the potential of dopants to introduce novel spin-correlated optical functionalities into 2D magnetic materials.