Effects of alkali ions on the optical properties, bandwidth flatness, and gain coefficient of near-infrared emission spectra of Er3+-doped zinc silicate glass

In this paper, we investigate and report the effects of alkali ions A⁺ (A⁺ = Li⁺, Na⁺, K⁺) on the optical properties, bandwidth flatness (BFN), gain coefficient (G(λ)) for the near-infrared (NIR) emission spectra of Er³⁺-doped SiO₂–ZnO–La₂O₃ (SZL) zinc silicate glass. With the change in the composition of A⁺ ions in the order from not containing any A⁺ ions → Li⁺ → Na⁺ → K⁺ → containing all three A⁺ ions including Li⁺, Na⁺, and K⁺, the direct and indirect bandgap (DBG and IBG), the absorption cross-section (σ_abs(λ)), the emission cross-section (σ_ems(λ)), and the G(λ) parameters of Er³⁺-doped SZL glasses were determined to increase gradually. NIR emission intensities of Er³⁺-doped at ⁴I_13/2 → ⁴I_15/2 transition under excitations of both 808 and 980 nm LD all were significantly increased with the composition of A⁺ ions varies in order from not containing A⁺ ions → Li⁺ → Na⁺ → K⁺ → containing all three A⁺ ions. The reasons for the influence of A⁺ ions on the UC and NIR emission intensities of Er³⁺-doped in SZL glass are investigated and discussed. In addition, upconversion (UC) emission spectra of Er³⁺-doped, CIE 1931(x; y) coordinates and color region for UC emission spectra of Er³⁺-doped SZL glasses with different compositions of A⁺ ions under excitation of 980 nm laser diode (LD) are also determined.