[en] Infrared-to-visible frequency upconversion through cooperative energy-transfer and thermal effects in Tb³⁺/Yb³⁺-codoped tellurite glasses excited at 1.064 μm is investigated. Bright luminescence emission around 485, 550, 590, 625 and 655 nm, identified as due to the ⁵D₄→⁷F_J (J=6, 5, 4, 3, and 2) transitions of the terbium ions, respectively, was recorded. The excitation of the ⁵D₄ emitting level of the Tb³⁺ ions is assigned to cooperative energy-transfer from pairs of ytterbium ions. The effect of temperature on the upconversion process was examined and the results revealed a fourfold upconversion enhancement in the 300-500 K interval. The enhancement of the upconversion process is due to the temperature dependence of the Yb³⁺-sensitizer absorption cross-section under anti-Stokes excitation. A rate-equation model using multiphonon-assisted absorption for the ytterbium excitation combined with the energy migration effect between Yb-Yb pair and Tb³⁺ ground-state depopulation via multiphonon excitation of the ⁷F_J excited states describes quite well the experimental results