Fig. 1. (a) DSC curves of PG. (b) XRD patterns of PG and glasses heat treated at different temperatures for 10 h. (c) XRD refinement patterns of glass heat treated at 480°C for 10 h.

Fig. 2. Crystal structure of (a) BaF₂ and (b) PbS doped with a Tm³⁺ ion.

Fig. 3. (a) TEM image and (b), (c) HRTEM images of the glass heat treated at 470°C for 10 h. (d) HAADF-STEM image and (e)–(i) the distribution of representative S, Pb, Ba, F, and Tm elements by two-dimensional element mapping of the glass heat treated at 470°C for 10 h.

Fig. 4. Absorption spectra of PG and glasses heat treated at different temperatures for 10 h.

Fig. 5. (a) PL spectra of PG and glasses heat treated at different temperatures for 10 h excited by an 808 nm laser. (b) PL spectra of the glass heat treated at 470°C; PL1 and PL2 are the luminescence bands related to the PbS QDs and Tm³⁺ ions. (c) Lifetime decay curves of the glass samples. The inset is the enlarged curves. The excitation wavelength is 808 nm, and the emission wavelength is 1810 nm. (d) Power-dependent PL spectra of the glass heat treated at 470°C. The inset is PL intensity of the luminescence bands related to the PbS QDs and Tm³⁺ ions.

Fig. 6. (a) Temperature-dependent PL spectra of glass heat treated at 460°C. (b) Temperature dependence of the PbS QDs PL peak position. (c) The FIR of I_Tm/I_QDs as a function of temperature in the range of 310–453 K. (d) The relative sensitivity S_R and the absolute sensitivity S_A in (c).