Broadband mid-infrared 2.8 μm emission in Ho3+/Yb3+-codoped germanate glasses

This work reports the mid-infrared emission properties around 2.85 μm in Ho3+/Yb3+ codoped germanate glasses. The glass not only possesses considerably low OH− absorption coefficient (0.24  cm−1), but also exhibits low phonon energy (790  cm−1). A large spontaneous transition probability (36.66 s−1) corresponding to the Ho3+:5I6→5I7 transition has been calculated based on the Judd-Ofelt theory. Besides, a broad 2.85 μm fluorescence has been successfully observed and a reasonably model has been proposed to unravel the origin of the broadening emission band. Moreover, the peak emission cross sections of the glass is as high as 9.2×10−21 cm2, and the maximum gain per unit length at 2.85 μm could be as high as 4.3 dB/cm. Results indicate that the prepared germanate glass is a promising candidate for 2.85 μm mid-infrared laser materials applications.