Enhancing thermometric performance via improving indicator signal in Bi3+-doped CaNb2O6:Ln3+ (Ln = Eu/Sm/Dy/Tb) phosphors

Currently, phosphor materials play an important role in designing noncontact remote optical thermometers. Although many approaches have contributed to improve thermometric performance of optical thermometers including optimization of host materials, size of nanoparticles, dopant type and concentration as well as excitation density and phonon energy engineering, the development of highly sensitive optical thermometric materials is still a challenge. Hence, we developed novel CaNb2O6 (CNO):Ln(3+) (Ln(3+) = Eu3+/Sm3+/Dy3+/Tb3+) phosphors as highly thermometric materials and proposed a novel strategy for further enhancing its thermometric performance via adding the intensity of indicator signal by co-doping Bi3+ ions in current phosphor system. Typically, the as-prepared CNO:Ln3+ phosphors present a broad blue emission around 470 nm originated from NbO6 octahedral groups and some respective emission lines derived from the characteristic f-f transitions of Ln(3+) ions. Based on the diverse thermal quenching performance between blue emission and Ln(3+) ions emission, the temperature sensitivities of CNO:Ln(3+) were investigated in detail. Among them, the maximum relative sensitivity of CNO:Eu3+ sample reached 1.991% K-1 in the range of 298-448 K and remained 97% after five temperature cycles. Furthermore, an obvious discoloration was discovered during temperature cycle testing in CNO:Ln(3)+ samples under 254 nm UV lamp. Through doping Bi3+ ion, the strongest intensity of indicator signal is 24 folds that of CNO host. Correspondingly, the relative sensitivity of CNO:Bi3+, Eu3+ sample is obviously improved to 3.793% K-1 in the range of 298-523 K, owing to a larger range of the FIR value and a wider drop range of indicator signal. This work opens up an effective pathway to improving thermometric performance of optical thermometers by enhancing the intensity of indicator signal of employed phosphor materials.