Ultrahigh-sensitive optical temperature sensing based on quasi-thermalized green emissions from Er:ZnO

Fluorescence intensity ratio (FIR) based optical temperature sensors employ the variation of intensity ratio between two peaks, which are very close to each other. Here, we prepare Er doped ZnO microrods by a hydrothermal route and exploit them for FIR based temperature sensing. The Er: ZnO shows the band-to-band UV emission and broad defect emissions with small Er3+ related peaks upon excitation with a 355 nm laser, while only peaks corresponding to Er3+ transitions are observed with 532 nm laser excitation. The green emissions (H-2(11/2) -> I-4(15/2), S-4(3/2) -> I-4(15/2)) under 532 nm excitation are considered for temperature sensing performance as they possess a quasi-thermal equilibrium between them and the variation of intensity ratio with temperature follows a Boltzmann type distribution. The sensitivity obtained here is very high (3445/T-2 K-1) compared to the reported Er3+ ion based temperature sensors and can be applied in a wide range of temperature (83-493 K). The value of sensitivity is found to be almost independent of the concentration of Er doping and is the highest reported for Er-doped materials.