AbstractThe transparent Er³⁺‐Yb³⁺‐doped fluoro‐aluminosilicate glass‐ceramic (GC) was prepared by melt‐quenching. The crystal phase, morphology, and up‐conversion (UC) luminescence of as‐produced GC were characterized by X‐ray diffraction, scanning electron microscopy, and fluorescence spectrophotometry, respectively. The results show that BaYF₅ nanocrystals were uniformly distributed in the glass matrix of the as‐produced GC. When the as‐produced GC was subjected to heat treatment, the crystallinity was increased, but the crystal identity remains unchanged. Such heat‐treatment doubled the intensity of the UC luminescence, and this enhancement was ascribed to the increased incorporation of both Er³⁺ and Yb³⁺ ions into the lower phonon energy environment of BaYF₅ nanocrystals. Furthermore, the heat‐treated GC was stable against further crystallization, and consequently its UC luminescence was stable at the application temperature. The heat‐treated GC was found to possess an outstanding temperature‐sensing capability.