Ratiometric fluorescence temperature-sensing properties of Eu3+ and Tm3+ in Gd4.67Si3O13 oxide host

A series of Eu3+ and Yb3+-Tm3+ doped Gd4.67Si3O13 (GS) phosphors were designed by using solid-state reaction method, and their photoluminescence properties were studied for optical temperature sensing applications. Single-phase samples were checked from XRD patterns and Rietveld refinement. Strong red emission of Eu3+ was obtained in the GS:Eu3+ phosphors upon 393 nm excitation. By employing the emissions from D-5(1) and D-5(0) levels of Eu3+, it has been found that the ratio of 535 and 577 nm emission intensities follows a linear relationship with absolute temperature. High sensitivities were obtained in the 5 mol% Eu3+ doped GS phosphor. It is important to find that the relative sensitivity shows a larger value at higher temperature, indicating the phosphor is more suitable to be used at relatively high temperature. By codoping Yb3+ and Tm3+ into the GS host, the upconversion (UC) luminescence of Tm3+ was received. The corresponding UC luminescent features and mechanism were investigated from the decay curves and pump-power-dependent spectra. Two kinds of fluorescence intensity ratio techniques were employed for the optical temperature sensing, i.e., I-697/I-648 and I-697 /I-789. The high relative sensitivity (S-R) and small S-R variation interval for I-697/I-648 reveal good optical temperature-sensing performance. Owing to the large energy gap between H-3(4) and F-3(3) levels of Tm3+, high S-R value can be achieved for I-697/I-789.