Metal–organic frameworks (MOFs) have emerged as powerful platforms for tuning the luminescence characteristics of guests due to their various structures and functions. Tunable and stimuli-responsive luminescence of guests within MOFs can be achieved through a judicious choice of guests and hosts. Herein, we demonstrate a dramatic change in the luminescence of dye excimers encapsulated in MOFs. A polar dye presented largely red-shifted excimer emissions in MOFs with higher polarities, while a nonpolar dye showed very different excimer emissions. Interestingly, the excimer emissions tailored by the MOFs showed strong thermal quenching. Cz-Ant@ZIF-8, containing two luminescent dyes (carbazole (Cz) and anthracene (Ant)), was prepared, and it presented ratiometric temperature sensing properties (1.55% K–1) in the temperature range of 278–353 K. This work sheds light on the luminescence tuning of dyes confined in MOFs and the design of sensitive ratiometric thermometers.