The effects of Yb3+ and Er3+ dopants on the optical and thermal properties and chemical durability of 40ZnF2-10Al2O3-50P2O5 glasses (nominal molar composition) have been investigated. The glass transition temperature (Tg), dilatometric softening temperature (Ts), crystallization temperature (Tc), refractive index, density, and durability in water increase with increasing Er3+ and Yb3+ contents, whereas the thermal expansion coefficient decreases. Red (645 nm) and near infrared (1.535 μm) emissions are simultaneously observed at room temperature with excitation at 980 nm. The red up-conversion and 1.5 μm emission spectra are associated with the 4F9/2 →4I15/2 and 4F13/2 →4I15/2 transitions of Er3+, respectively, and the up-conversion excitation processes have been analyzed. The Yb3+ ions enhance the up-conversion and emission processes. The results suggest that the Er3+/Yb3+-codoped ZnF2-Al2O3-P2O5 glasses may be a potential material for developing optical amplifiers and up-conversion optical devices.