Mixing up-conversion excitation behaviors in Er³⁺/Yb ³⁺-codoped aluminum germanate glasses for visible waveguide devices

A mixing up-conversion excitation phenomenon in Er³⁺/Yb ³⁺-codoped aluminum germanate (Na₂O-MgO-Al ₂O₃-GeO₂, NMAG for short) glasses for K ⁺-Na⁺ ion-exchanged waveguides was observed and characterized. The green and red up-conversion luminescence of Er³⁺ is due to a two-photon excitation process under low-power excitation of a 974 nm diode laser, however, with increasing the pumping power, the green emission turns to follow a combination of two- and three-photon excitation effects while the red one still agrees with a two-photon excitation law. Under high-power pumping, owing to potential thermal effect, the population ratio between the ²H_11/2 and ⁴S_3/2 levels adjusts acutely, which results in a distinct exhibition in ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 emission transitions. Green transmission trace has been observed in K⁺-Na⁺ ion-exchanged Er ³⁺/Yb³⁺-codoped NMAG glass waveguide and it provides an original reference in developing visible waveguide amplifiers and lasers.