Infrared-to-visible upconversion flurescence of Er/Yb-codoped bismuthate glasses

Er³⁺/Yb³⁺-codoped bismuthate glasses for developing potential upconversion lasers have been fabricated and characterized. The optimal Yb³⁺ doping content was investigated in the glasses with different Yb³⁺-Er³⁺ concentration ratios and the optimal Yb³⁺-Er³⁺ concentration ratio is 5:1. Under 975 nm excitation, intense green and red emissions centered at 525, 546 and 657 nm, corresponding to the transitions ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2, respectively, were observed at room temperature. The quadratic dependence of the 525, 546 and 657 nm emissions on excitation power indicates that a two-photon absorption process occurs under 975 nm excitation.