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

• Influence of F− on the reduction process of Eu3+ to Eu2+were investigated. • Direct/indirect optical bandgaps of Eu3+/Eu2+–Er3+–Yb3+ co-doped were calculated. • CIE for VIS emissions of Eu3+/Eu2+–Er3+–Yb3+ co-doped was identified. • Energy transfer process between Eu3+/Eu2+ and Er3+ was also discussed. In this paper, we report the influences of F− ions on the reduction process of Eu3+ to Eu2+, and the optical properties of Eu3+/Eu2+–Er3+–Yb3+ co-doped niobate silicate glasses. The visible (VIS), upconversion (UC) emissions, and energy transfer (ET) of Eu3+/Eu2+–Er3+–Yb3+ 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 Eu3+/Eu2+–Er3+–Yb3+ 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 Eu3+ to Eu2+were also investigated and discussed. [ABSTRACT FROM AUTHOR]