Our findings show how semiconducting inorganic complexes with low vibrational energies can be used to enhance the optical properties of UCNPs while seamlessly facilitating the fabrication of a low-phonon-energy matrix that allows UCNPs to be accessed electronically. With further optimization, this approach should be extensible to other UCNP host materials and other nanoscale emitters that can benefit from a non-epitaxial, low-vibrational-energy environment.