Metal-dielectric nanocavities have the ability to tightly confine light to small mode volumes resulting in strongly increased local density of states. Placing fluorescing molecules or semiconductor materials in this region enables wide control of radiative processes including absorption and spontaneous emission rates, quantum efficiency, and emission directionality. In this talk, I will describe our recent experiments utilizing a tunable plasmonic platform where emitters are sandwiched in a sub-10-nm gap between colloidally synthesized silver nanocubes and a metal film. Utilizing dye molecules with an intrinsic long lifetime reveals spontaneous emission rate enhancements exceeding a factor of 1,000 while maintaining directional emission and high quantum efficiency [Akselrod et al. Nature Photon. 8, 835 (2014)]. Incorporating colloidal CdSe/ZnS semiconductor quantum dots into the nanocavities enables ultrafast spontaneous emission with rates exceeding 90 GHz [Hoang et al., Nat. Commun. 6, 7788 (2015)] as well as ultrafast and efficient single photon sources [Hoang et al., Nano Lett., Article ASAP (2015)]. Leveraging higher-order modes of the cavity allows optical processes at multiple energies to be optimized simultaneously. We demonstrate this by enhancing both the absorption and the quantum yield in monolayer MoS2 resulting in a 2,000-fold enhancement in the overall fluorescence [Akselrod et al., Nano Lett. 15, 3578 (2015)]. Finally, this nanocavity geometry can be tuned from the visible to the near-infrared using large-area solution-based deposition techniques [Akselrod et al., Adv. Mater. 27, 7897 (2015)] promising for future ultrafast and highefficiency optoelectronic devices.