A new intensity ratio method based on the reabsorption effect was evaluated by Luis Humberto da Cunha Andrade and co‐workers (see article number 1900484), using an Sm2+:KCl crystal, for fluorescent sensor applications. Spectroscopic characterization showed that the material could be excited in a broad wavelength range with the emission band maintaining its shape and maximum position, centered at 750 nm at 300 K. The obtained sensitivities and blueshift, together with the high quantum yield found for the Sm2+:KCl crystal, indicate that the material and the new methodology have characteristics suitable for their application in the development of fluorescent temperature sensors. – The cover article belongs to a collection of 19 articles on “Optical Materials (IS‐OM8)” assembled in this issue and guest‐edited by Joanna Cybińska, Małgorzata Guzik, and Akira Yoshikawa (see Editorial, article number 2000386).