Infrared to visible upconversion in Er3+-doped-lead-germanate glass: Effects of Er3+ ion concentration

Abstract

The upconversion mechanism of Er³⁺ ions has been studied for lead‐germanate glasses containing Er₂O₃ concentrations from 0.1 mol % to 2 mol %. Intense green emission was observed at room temperature due to ⁴S_3/2→⁴I_15/2 transition excited by a cw near‐infrared laser beam at 797 nm. This green emission shows a similar intensity for samples with different Er³⁺ ion concentrations. A weak blue emission of 410 nm originating from the ²H_9/2→⁴I_15/2 transition was also observed. This blue emission and a red emission from the ⁴F_9/2 level increase with the increase in Er³⁺ ion concentration. The bright green emission is attributed to the excited level absorption while the blue emission is due to a third step excitation where energy transfer between excited ions owing to their Coulomb interaction plays a key role.