This study reveals that the interaction between a 2D material and its substrate can significantly modify its electronic and optical properties, and thus can be used as a means to optimize these properties. High-temperature (25–500 ℃) optical spectroscopy, which combines Raman and photoluminescence spectroscopies, is highly effective for investigating the interaction and material properties that are not accessible at the commonly used cryogenic temperature (e.g., a thermal activation process with an activation of a major fraction of the bandgap). This study investigates a set of monolayer WS₂ films, either directly grown on sapphire and SiO₂ substrates by CVD or transferred onto SiO₂ substrate. The coupling with the substrate is shown to depend on the substrate type, the materialsubstrate bonding (even for the same substrate), and the excitation wavelength. The inherent difference in the states of strain between the as-grown and the transferred films has a significant impact on the material properties.