Influence of F− on the reduction process of Eu3+ to Eu2+ and optical properties of Eu3+/Eu2+–Er3+–Yb3+ co-doped niobate silicate glasses

In this paper, we report the influences of F ⁻ ions on the reduction process of Eu ³⁺ to Eu ²⁺, and the optical properties of Eu ³⁺/Eu ²⁺–Er ³⁺–Yb ³⁺ co-doped niobate silicate glasses. The visible (VIS), upconversion (UC) emissions, and energy transfer (ET) of Eu ³⁺/Eu ²⁺–Er ³⁺–Yb ³⁺ co-doped niobate silicate glasses under the excitations of 295, 335 nm, and 980 nm laser diode (LD) were investigated. The direct/indirect optical bandgaps and CIE 1931 (x; y) chromaticity coordinates for luminescence of Eu ³⁺/Eu ²⁺–Er ³⁺–Yb ³⁺ co-doped niobate silicate glasses under the excitations of 295, 335 nm were also been calculated and identified. Remarkably, the influences of F ⁻ ions and experimental conditions platinum crucibles with the lid on enhancing the reduction process of Eu ³⁺ to Eu ²⁺were also investigated and discussed.