Excitation-dependent enhancement and quenching of the 1.54 μm emission from Er³⁺ ions in dichroic Cu nanocomposite glass

The 1.54 μm emission of Er³⁺ ions embedded in a dichroic Cu nanocomposite glass is shown to be either quenched or enhanced depending on the excitation wavelength. The synthesized material consisted of an aluminphosphate matrix co-doped with Cu and Er as prepared by thermal processing, and characterized by optical absorption and photoluminescence (PL) spectroscopy including an assessment of decay dynamics. The extinction spectrum presented a broad surface plasmon resonance (SPR) band for Cu nanoparticles (NPs) around 588 nm, while the glass appeared to scatter red light but transmit blue, i.e. exhibiting dichroism. Interestingly, the PL obtained for the ⁴I_13/2 → ⁴I_15/2 emission around 1.54 μm was enhanced under the excitation of the ⁴I_15/2 → ⁴F_9/2 transition at 650 nm, which turned out to be located toward the low energy wing of the SPR of Cu NPs. About a 12% PL boost was estimated relative to a merely Er³⁺-doped reference. Conversely, a PL quenching effect was manifested for resonant Er³⁺ excitations (e.g. ⁴I_15/2 → ²H_11/2 transition at 520 nm) overlaid with the 3d → 4sp interband transitions absorption in copper. It is suggested that favorable conditions for the PL enhancement are achieved for when the excitation of Er³⁺ ions can benefit from light scattering by plasmonic Cu particles, while an excitation energy transfer from Er³⁺ to Cu NPs via interband transitions leads to the quenching.