Resonant near-infrared emission of Er³⁺ ions in plasmonic arrays of subwavelength square holes

Periodic nanostructure arrays consisting of square holes were fabricated with a Focused Gallium Ion Beam on a gold thin film deposited onto the surface of an Er³⁺-doped tellurite glass. The nominal dimensions of the square elements are approximately 300×300 nm2, separated by 1.0 μm, such that we have arrays of approximately 15×15, 10×10 and 5×5 μm2 dimensions. The metallic nanostructures were vertically illuminated with a diode laser at 405 nm. The Er³⁺ luminescence spectrum in the near-infrared was measured in the far-field via the micro-luminescence technique. The excitation and emission of the Er³⁺ ions were obtained through of the so-called extraordinary optical transmission of excitation and emission light, respectively, via those squares array. In this way, metallic nanostructures sustaining surface plasmons can excite and change the emission properties of the Er³⁺ ions. Additional contributions on the emission spectra were achieved due to the influence of the gold metal film, i.e., the resonant properties from the plasmonic nanostructures can strongly influence the spectroscopic features of the Er³⁺ ions. Therefore, we present a systematic quantum mechanical experiment that shows the quantum plasmonic properties of these nanostructure arrays on the erbium ions, with direct applications for understanding and exploiting of nanophotonic devices.