the volume, and thus, the antenna efficiency $^{7,39}$. The nanocone antenna is similar to the (bi-) conical antenna, which is the canonical example of a broadband antenna for applications in the VHF and UHF frequency bands. 26 However, for practical reasons such as the antenna weight, it is often realized in the form of a bow-tie. Finite and semi-infinite metal nanocones are not a new concept in optics and SNOM. 40–44 For example, conical SNOM probes could be exploited to focus surface plasmon-polaritons down to a spot size limited only by the tip curvature. 45–48 Moreover, the field enhancement for semi-infinite 49 and finite 50,51 silver nanocones has been studied as a function of the cone angle. In both situations, like for the bow-tie $^{27}$, there exists an optimal angle that maximizes the enhancement. Moreover, it was pointed out that a finite nanocone can give rise to a stronger field than a semi-infinite one because of the LSPP resonance effect. 52,53 Other groups investigated the modification of fluorescence lifetime by semi-infinite metal tips, 54–56 where coupling to the surface plasmon-polariton mode leads to quenching. Also for finite nanocones, previous investigations concluded that quenching dominates at the LSPP resonance. 57 Here, we concentrate our attention on finite 3D gold nanocones to demonstrate that they can actually exhibit very interesting performances in terms of Purcell effect and antenna efficiency at the LSPP wavelength. In particular, we discuss the role of η$_{a}$ in determining the optimal angle for enhancing fluorescence. First, we briefly review the theory and com- putational approach for studying spontaneous emission and molecular fluorescence with an optical antenna. Second, we investigate F and η$_{a}$ of single and double gold nanocones as a function of cone angle. We then discuss the role of the emitter intrinsic quantum effi- ciency η o , which together with F and η$_{a}$ determines the effective quantum efficiency and the fluorescence enhancement. Lastly, we explore the effect of a supporting substrate and of rounding the tip. We consider an isolated emitter with radiative decay rate γ r $_{o}$, nonradiative decay rate γ nr o and quantum efficiency η o = γ r $_{o}$/ ( γ r o + γ nr o ). The presence of a metal nanostructure modifies II. RESULTS AND DISCUSSION A. Theory and computational details 4