The composite with 9-nm UCNPs (Figure ) exhibits interconnected nanoscale nodules, significantly different than the original Sn2S6 4--capped UCNPs, which were clearly separated (Figure ). These nodules are attributed to the formation of a SnS2 matrix made from the decomposition and fusing of the Sn2S6 4-ligands. An alternative hypothesis is that these nodules are from the sintering and grain growth of the NaYF4 UCNPs themselves. However, this hypothesis can be rejected since powder X-ray diffraction peaks do not significantly narrow following annealing (Figure ), indicate no significant increase in the size of the NaYF4 domains. Our analyses thus support the formation of nanoscale upconverting emitters embedded in a semiconducting matrix. This composite allows the desirable optical properties of UCNPs to be retained while adding the important capability to electronically interface with each UCNP through the semiconducting matrix.