Fig. 1. Flow chart preparation of FeS QDs

Fig. 2. The morphology, structure and component characterizations of FeS QDs. (a) TEM image (inset shows the particle size distribution); (b) HR-TEM image; (c) Crystal structure model; (d) AFM image; (e) Height analysis of the particle sizes at positions 1, 2, and 3 marked in Fig.(d); (f) EDS energy spectrum

Fig. 3. The component, chemical bond, phase and vibrational spectrum analysis of FeS QDs (a) XPS full spectrum; (b) S 2p XPS spectrum; (c) Fe 2p XPS spectrum; (d) FTIR spectrum; (e) XRD diffraction pattern; (f) Raman spectrum

Fig. 4. UV-Vis absorption spectrum of FeS QDs and FeS QDs/PVA nanocomposite films. (a) FeS QDs solution, (inset: FeS QDs solution under natural light and UV light); (b) FeS QDs films; (c) PVA films and FeS QDs/PVA composite films (inset: photographs of PVA films (right) FeS/PVA composite films (left))

Fig. 5. PL and PLE spectra of FeS QDs and FeS QDs/PVA nanocomposite films. (a) PL plots of FeS QDs (inset: PL plots of NIR); (b) PL plots of FeS QDs normalised; (c) PLE plots of FeS QDs (inset: PLE plots in NIR); (d) PLE plots of FeS QDs normalised; (e) PL plots of FeS QDs/PVA composite films (inset: PL plots of the composite films in NIR); (f) PL plots of FeS QDs/PVA composite films normalised