Excited-state absorption in Er:BaY2F8 and Cs3Er2Br9 and comparison with Er:LiYF4

The influence of Excited-State Absorption (ESA) on the green laser transition and the overlap of Ground-State Absorption (GSA) and ESA for 970 nm upconversion pumping in erbium is investigated in Er3+:BaY2F8 and Cs3Er2Br9. Results are compared to Er3+:LiYF4. In Er3+:BaY2F8, a good overlap between GSA and ESA is found at 969 nm in one polarization direction. The emission cross section at 550 nm is a factor of two smaller than in LiYF4. In Cs3Er2Br9, the smaller Stark splitting of the levels shifts the wavelengths of the green emission and ESA from I-4(13/2) off resonance. It enhances, however, ground-state reabsorption. The emission cross section at 550 nm is comparable to LIYF(4). Upconversion leads to significant green fluorescence from H-2(9/2). A significant population of the I-4(11/2) level and ESA at 970 nm are not present under 800 nm pumping.