Broadband 2 μm fluorescence and energy transfer evaluation in Ho³⁺/Er³⁺ codoped germanosilicate glass

This work reports the broadband 2 μm emission from Ho³⁺/Er³⁺ codoped germanosilicate glasses. Spectral components of the 2 μm emission band were analyzed and an equivalent model of four-level system was proposed to describe the 2 μm emission band. The results suggested that Ho³⁺/Er³⁺ codoped germanosilicate glass has high effective emission bandwidth (172 nm), large emission cross section (5.18×10⁻²¹ cm²) and gain bandwidth (891×10⁻²⁸ cm³), which is a promising candidate for 2 μm laser and amplifier. In addition, energy transfer mechanism between Ho³⁺ and Er³⁺ ions was investigated based on the measured fluorescence spectra and decay curves of Er³⁺:⁴I_11/2 and ⁴I_13/2 levels. Energy transfer efficiency and microscopic parameters were calculated to evaluate the 2 μm fluorescence. Moreover, a rate equation model between Ho³⁺ and Er³⁺ ions was developed to elucidate 2 μm fluorescence behaviors. This work might provide useful guide to investigate fluorescence behavior and energy transfer mechanism of rare earth ions. - Highlights: • Ho³⁺/Er³⁺ codoped germanosilicate glasses were prepared. • Spectral components of the 2 μm emission band were analyzed. • Emission bandwidth, emission cross section and gain bandwidth were calculated. • Energy transfer mechanism between Ho³⁺ and Er³⁺ ions was investigated. • A rate equation was developed to elucidate 2 μm fluorescence behaviors