Broadband Optical Properties of Atomically Thin PtS₂ and PtSe₂

Noble transition metal dichalcogenides (TMDCs) such as PtS₂ and PtSe₂ show significant potential in a wide range of optoelectronic and photonic applications. Noble TMDCs, unlike standard TMDCs such as MoS₂ and WS₂, operate in the ultrawide spectral range from ultraviolet to mid-infrared wavelengths; however, their properties remain largely unexplored. Here, we measured the broadband (245-3300 nm) optical constants of ultrathin PtS₂ and PtSe₂ films to eliminate this gap and provide a foundation for optoelectronic device simulation. We discovered their broadband absorption and high refractive index both theoretically and experimentally. Based on first-principle calculations, we also predicted their giant out-of-plane optical anisotropy for monocrystals. As a practical illustration of the obtained optical properties, we demonstrated surface plasmon resonance biosensors with PtS₂ or PtSe₂ functional layers, which dramatically improves sensor sensitivity by 60 and 30%, respectively.