Annealing of the Na4Sn2S6 ligand without UCNPs resulted in a film with a characteristic SnS2 Raman peak at 314 cm -1 (Figure , green line). Upon annealing the Sn2S6 4--capped UCNPs at 350 °C to form the UCNP-SnS2 composite, we observed the disappearance of the 182 cm -1 peak and the weakening of the 360 cm -1 peak, consistent with the decomposition of Sn2S6 4-(Figure , blue line). The identification of the SnS2 peak for the UCNP-SnS2 is more challenging due to interfering NaYF4 peaks. Scanning electron microscopy further supports the formation of a UCNP-SnS2 composite.