Investigations on the broadband fluorescence of Yb/Nd co-doped silica glass with low -OH content derived from modified sol-gel method

The inherent limitations of the MCVD technique continue to pose persistent challenges in fabricating Yb 3+ -doped silica glasses with both superior homogeneity and high doping concentrations. Furthermore, the emission bandwidth of Yb 3+ remains fundamentally constrained by the intrinsic 4f→4f electronic transitions, resulting in characteristically narrow FWHM spectral profiles that significantly restrict practical laser applications. This study presents a modified sol-gel approach for fabricating Yb-Nd co-doped silica glasses with exceptionally high rare-earth ion concentrations and low hydroxyl group content. Through vacuum-assisted melting, we successfully reduced residual -OH content to 2.08 ppm while achieving high Yb 3+ doping levels. The co-doping architecture induced remarkable spectral broadening , the fluorescence band exhibiting a 108 nm FWHM through synergistic overlap of Yb 3+ and Nd 3+ emission profiles. Systematic analysis revealed an efficient unidirectional energy transfer mechanism from Nd 3+ to Yb 3+ , reaching peak transfer efficiency of 76.02 % in the optimal 0.5 mol% Yb 3+ -1.5 mol% Nd 3+ composition.