Erbium-activated aluminum fluoride glasses: optical and spectroscopic properties

Absorption and luminescence measurements have been performed on aluminum fluorophosphate glasses in the system AlF3–MgF2–CaF2–SrF2–BaF2–YF3–ZrF4–NaPO3, doped with 0.1 and 1 mol% Er3+. A green-to-blue upconversion fluorescence has been observed upon continuous-wave excitation at 514.5 nm. The upconversion intensity has a quadratic dependence on the incident pump power, indicating that two photons are responsible for the frequency upconversion process. The main mechanisms that produce the upconversion are excited state absorption and energy transfer among erbium ions. Emission in the third telecom window (1.5 μm) has been measured upon excitation at 514.5 nm.