Er3+ and xYb3+ co-doped CdO–V2O5–P2O5 invert glasses were studied through their structural, optical and photoluminescent properties as a function of the incorporation of Yb3+ ions. From XRD was observed that the glass system remains amorphous up to Yb3+ concentration of 4.0 mol%. Raman Spectroscopy revealed that the samples are composed by amorphous Cd2V2O7 and PO4 units, with a maximum phonon energy of 923 cm−1. The optical bandgap values calculated by Tauc's method were in the range of 2.47–2.70 eV, depending on the Yb3+ content. Furthermore, Burstein-Moss effect on the optical bandgap was observed for Yb3+ concentration higher than 1.0 mol%, like heavy doped semiconductors. Such fact is followed by a reduction of the Urbach energy from 0.70 to 0.35 eV. The Er3+:(2H11/2, 4S3/2) → 4I15/2, 4F9/2 → 4I15/2 up conversion and 4I13/2 → 4I15/2 downshifting emissions upon 980 nm laser excitation, are gradually improved with the Yb3+ content. A maximum enhancement of 20 and 80 times for both green and red up conversion emission was achieved, respectively, whereas the NIR downshifting emission was improved about 5.3 times for 4.0 mol% of Yb3+, regarding the singly Er3+ doped glass. Such effect is partially related to the Burstein Moss effect and an efficient energy transfer from Yb3+ to Er3+.
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