In this study, we investigated the surface functionalization of lanthanide-doped UCNPs with Sn2S6 4-inorganic metal complexes and verified the ligand exchange via Raman spectroscopy and EDS elemental mapping. We found that the Sn2S6 4-ligands can enhance the UCL intensity of both Yb 3+ /Tm 3+ -and Yb 3+ /Er 3+ -doped UCNPs, with enhancement factors up to 16 for small, highly doped UCNPs. Upon annealing, these Sn2S6 4--capped UCNPs can also be transformed into a nanocomposite of UCNPs embedded within a matrix of semiconducting SnS2. This nanocomposite can be used to harness the nonlinear optical properties of UCNPs in charge-based devices such as photodetectors. To demonstrate this, we tested a proof-of-concept UCNP-SnS2 device that displays photoconductive behavior under both UV and NIR light.