Gold plasmonic lenses consisting of planar concentric rings with different periods were milled with a Focused gallium Ion Beam on a gold thin film deposited onto an Er³⁺-doped tellurite glass. The plasmonic lenses were vertically illuminated with an argon ion laser (558 nm) highly focused by means of a 20x objective lens. The focusing mechanism of the plasmonic lenses is explained by using a simple coherent interference model of surface plasmon-polariton (SPP) generation on the circular grating as a result of the incident field. As a result, phase modulation can be accomplished by the groove depth profile, similar to a nano-slit array with different widths. This focusing allows a high confinement of SPPs which excited the Er³⁺ ions of the substrate. We analyze the influence of physical and geometrical parameters on the luminescence spectra. The variation of these parameters resulted in considerable changes of the luminescence spectra.