Spectroscopic investigation of the influence of Cu⁺ ions and plasmonic Cu particles on Ho³⁺ luminescence in phosphate glass

The luminescence of Ho³⁺ ions in phosphate glass containing a high concentration of Cu⁺ ions and also Cu nanoparticles (NPs) is reported. The glasses consisting of a barium-phosphate matrix were obtained by thermal processing and characterized by Fourier transform-infrared spectroscopy (FT-IR), optical absorption, and photoluminescence (PL) spectroscopy. The FT-IR data appeared consistent with a network modifier role of Cu⁺ ions with no significant structural alteration induced by NPs. The absorption spectrum for heat-treated Cu⁺/Ho³⁺ co-doped glass exhibited narrow plasmon resonance for Cu NPs around 575 nm. It was indicated that Cu⁺ PL dominates for excitation resonant with Cu⁺ absorption. Conversely, Ho³⁺ emission is clearly displayed for excitation in the visible (e.g. 450 nm) away from Cu⁺ excitation. Precipitating Cu NPs resulted in suppression of Cu⁺ band emission and the Ho³⁺ PL being quenched. Following the assessment of Ho³⁺ emission dynamics, likely energy transfer processes involving Cu NPs as energy acceptors were proposed.