To examine the thermal effect on the PL

To examine the thermal effect on the PL behavior, the emission intensity of the Ca5(PO4)3F:6% Tb3+, 8% Eu3+ and the Ca5(PO4)3F:10% Tb3+, 6% Eu3+ was recorded at temperatures ranging from 98 to 573 K under the excitation at 258 nm (Fig. 5(a) and (b)). The emission intensities of both Tb3+ and Eu3+ ions in Ca5(PO4)3F:6% Tb3+, 8% Eu3+ show an obvious decrease with the rise in sample temperature. However, it Splitomicin is interesting that the intensity of Tb3+ (548 nm) exhibits a significantly different temperature-dependent luminescence behavior as compared to that of Eu3+ (621 nm) in Ca5(PO4)3F:6% Tb3+, 8% Eu3+ (Fig. 5(c)). The emission intensity of 548 nm (Tb3+) shows a linear temperature dependence whereas the 621 nm (Eu3+) emission is much less affected by the change of temperature and even a little bit increase in the 150–250 K temperature range. And it is also the same tendency of Ca5(PO4)3F:10% Tb3+, 6% Eu3+ sample (Fig. 5(d)). The different temperature-dependent luminescent emissions of 5D4→7F5 (Tb3+, 548 nm) and 5D0→7F2 (Eu3+, 621 nm) in the same host materials have enabled them to be excellent candidates for self-referencing luminescent thermometers [21]. Therefore, in planktonic organisms work, the emission intensity ratio of the 5D4→7F5 (Tb3+ at 548 nm) to 5D0→7F2 (Eu3+ at 621 nm) transition (denoted as ITb/IEu) is used as a self-calibrated reference for the sample temperature, such that the well-known drawbacks of one transition intensity-based measurements (e.g., quantity of the luminophore, excitation power or strong electromagnetic noise) can be easily circumvented. From 98 to 300 K the following linear dependence of ITb/IEu on temperature is found for:equation(1)ITb/IEu=1.782–0.0038TITb/IEu=1.782–0.0038Tequation(2)ITb/IEu=2.925–0.0053TITb/IEu=2.925–0.0053T