Multi‐phase glass‐ceramics containing CaF 2 : Er 3+ and ZnAl 2 O 4 :Cr 3+ nanocrystals for optical temperature sensing

Oxyfluoride transparent glass‐ceramics (GC) containing CaF 2 and ZnAl 2 O 4 nanocrystals have been fabricated with melt‐quenching method. By carrying out the heat treatment of the precursor glass (PG), Er 3+ and Cr 3+ were selectively partitioned into CaF 2 and ZnAl 2 O 4 nanocrystals, respectively. The obtained multi‐phase GC exhibited strong upconversion (UC) fluorescence of Er 3+ as well as intense down‐conversion (DC) fluorescence of Cr 3+ . Under 980 nm excitation, the green UC fluorescence of Er 3+ due to 2 H 11/2 , 4 S 3/2 → 4 I 15/2 transition and the red DC fluorescence lifetime of Cr 3+ due to 2 E, 4 T 2 → 4 A 2 transition were found to be highly dependent on the temperature and makes them possibly suitable for Optical Thermometry. With least‐square fitting methods, the FIR of Er 3+ from thermally coupled energy states ( 2 H 11/2 and 4 S 3/2 ) produced maximum temperature sensing sensitivity values of 0.33% K −1 at 437 K and 0.36% K −1 at 267 K, respectively. Similarly, fluorescence lifetime of Cr 3+ attributed to the parity forbidden ( 2 E → 4 A 2 ) and spin allowed ( 4 T 2 → 4 A 2 ) produced the maximum temperature sensor sensitivity value equal to 0.67% K −1 at 535 K.