Cooperite, or platinum sulfide (PtS), is a rare mineral that generally exists as microscale, irregularly shaped crystallites. The presence of impurities, in both naturally occurring and synthesized samples, has hindered the study of its optical properties in the past. In this work, we prepare large-scale, uniform PtS films in bulk to two-dimensional form through the thermally assisted conversion method. An abnormal trend is observed in linear spectral studies whereby the optical bandgap narrows as the film thickness decreases. A model based on the continuous distribution of carriers in real space, which can be regarded as a quantum well normal to the plane, is used to describe the thickness-dependent carrier recombination phenomenon. In the nonlinear optical measurements, PtS exhibits ultrafast saturable absorption and self-defocusing properties in the visible region, which are dominated by the resonant electronic nonlinearities.

Palladium diselenide (PdSe2) exhibits considerable potential for application in broadband optoelectronic devices. In this work, the broadband nonlinear optical performance and ultrafast carrier dynamics from ultraviolet to near‐infrared of a trilayer PdSe2 are systematically studied. PdSe2 is found to achieve a giant saturable absorption performance. The modulation depth is 22.47% at 520 nm, whereas the nonsaturable loss and saturation intensity are only 3.83% and 15.47 GW cm−2, respectively, which are better than those of many 2D semiconductors. Based on these findings, a PdSe2‐based visible light thresholder is proposed, its function is to extract an undetectable pulse signal drowned in strong stochastic noise and thereby improve the signal‐to‐noise ratio. Pump–probe technique, along with first‐principles calculation and transient absorption spectra, reveals the intrinsic recombination mechanism, including Auger scattering and trap saturation. This work is expected to establish the foundation for the development of next‐generation PdSe2‐based devices in optoelectronics and visible light communication.