Synthesis and Characterization of Functional 2D Metal Chalcophosphates for Air Force Applications and Technology

The invited talk will focus on the study of layered van der Waals (vdW) materials at The United States Air Force Research Laboratory, highlighting recent experimental and theoretical discoveries across the electronic, optical, magnetic, and vibrational domains, primarily within the metal phosphorus chalcogenide family. This field covers both new materials and new phenomena, including the interplay of magnetism, structure, and chiral phonons in AgCrP2Se6, the pressure-induced insulator-to-metal transition in CoPS3, and the effects of domain engineering on the ferrielectric transition of CuInP2S6-In4/3P2S6 heterostructures. Additionally, we note mode-selective spin-phonon coupling in MPX3 for (X=Mn, Fe, Co, Ni) which is largely dependent on the combination of electron valence and M-S distance. From the optical perspective we also show results for pressure and strain sensitivity in the multiband emitter AgErP2Se6. This material exhibits multi-band photoluminescence covering a wide range (350–1,550 nm) with ultra-narrow emission peaks. Its luminescence intensity ratios (LIRs) demonstrate high sensitivity for both temperature and pressure sensing applications. We also note that CuInP₂S₆ and AgScP2S6 exhibit high harmonic generation, with CuInP2S6 showing a signal up to the 10th order from a mid-IR driving field. Here,first-principles calculations suggest that electron-electron interactions play a critical role in enhancing the high-order optical nonlinearity, marking a pathway for designing nonlinear optical materials. Finally, our characterization work on ZnPS₃ also provides insight into its high thermal expansion and dimensional stability under extreme pressure. This talk will summarize the structure-property relationships in this unique family of 2D materials and highlight the profound potential of vdW materials for technologically relevant device physics.