The data presented in this dataset is published in: Gutiérrez, Y., Dicorato, S., Ovvyan, A. P., Brückerhoff-Plückelmann, F., Resl, J., Giangregorio, M. M., Hingerl, K., Cobet, C., Schiek, M., Duwe, M., Thiesen, P. H., Pernice, W. H. P., Losurdo, M., Layered Gallium Monosulfide as Phase-Change Material for Reconfigurable Nanophotonic Components On-Chip. Adv. Optical Mater. 2023, 2301564. https://doi.org/10.1002/adom.202301564 Experimental details on the structural and optical properties available in this respository are described in the Methods section. The files have the following structure: Refractive index files - files are structured in columns as: eV nm n k Raman files - files are structured in columns as: cm-1 counts Descriptions in the files: refractive_index_amorph_GaS.txt - Refractive index (n,k) of as deposited amorphous GaS. Data shown in Figure 1b of the manuscript. refractive_index_thermally_crystallized_GaS.txt- Refractive index (n,k) of thermallycrystallized GaS. Data shown in Figure 3c,d of the manuscript. refractive_index_laser_crystallized_GaS.txt - Refractive index (n,k) of laser crystallized GaS. Data shown in Figure 3i of the manuscript. Raman_amorph_GaS - Raman spectrum of amorphous GaS. Background substracted. Data shown in Figure 1a. Raman_cryst_GaS - Raman spectrum of crystalline GaS. Data shown in Figure 1a.