High content Er3+ doped ZBLAN glass: The spectral characteristics and high slope efficiency MIR laser investigation

•The high content (6.0 mol%) Er3+ ions doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fluoride glass sample with low OH- concentration (0.013 cm−1) was prepared.•The radiative trapping effect of Er3+ ions with different sample size has been investigated.•The numerical modeling results showed the mid-infrared output-laser improved greatly and even exceeded the Stokes limit.