2 μm emission properties and nonresonant energy transfer of Er 3+ and Ho 3+ codoped silicate glasses.

2.0 μm emission properties of Er3+ /Ho3+ codoped silicate glasses were investigated pumped by 980 nm LD. Absorption spectra were determined. Intense mid-infrared emissions near 2 μm are observed. The spectral components of the 2 μm fluorescence band were analyzed and an equivalent model of four-level system was proposed to describe broadband 2 μm emission. Low OH- absorption coefficient (0.23 cm-1 ), high fluorescence lifetime (2.95 ms) and large emission cross section (5.61 × 10-21  cm2 ) corresponding to Ho3+ : 5 I7 →5 I8 transition were obtained from the prepared glass. Additionally, energy transfer efficiency from the Er3+ : 4 I13/2 to the Ho3+ : 5 I7 level can reach as high as 85.9% at 0.75 mol% Ho2 O3 doping concentration. Energy transfer microscopic parameters (CDA ) via the host-assisted spectral overlap function were also calculated to elucidate the observed 2 μm emissions in detail. Moreover, the rate equation model between Er3+ and Ho3+ ions was developed to elucidate 2 μm fluorescence behaviors with the change of Ho3+ concentration. All results reveal that Er3+ /Ho3+ codoped silicate glass is a promising material for improving the Ho3+ 2.0 μm fiber laser performance.