L-band Er doped fiber (EDF) laser sources are in great demand for extending communication bandwidth. However, the gain performance is limited by the low emission cross section (σ_e) of Er³⁺ at wavelengths longer than 1590 nm. In our study, we revealed the mechanism of regulating Er emission behavior in silicate glass, and provided a linear model to predict the σ_e of Er-doped silicate glass with R² = 92.3%. The σ_e1600 was increased to 23.5 × 10⁻²² cm² through erbium coordination engineering. Results were elucidated using X-ray absorption fine structure (XAFS) spectra, molecular dynamics (MD) simulations and fluorescence. Furthermore, this work validates this model in Er doped silicate fibers and obtained >20 dB amplification in the range of 1585–1625 nm. This coordination engineering shows significant potential in applications of Er-doped silicate glasses and fibers. It provides an attractive prospect for expanding communication bandwidth by efficiently manipulating the emission of erbium to cover long wavelength.