Tm3+ doped and Tm3+/Yb3+ codoped lanthanum aluminum germanate (LAG) glasses are prepared by melt-quenching method and characterized optically. Based on the measurement of absorption spectrum, Judd–Ofelt intensity parameters (Ω2,Ω4,Ω6) are calculated. The radiation emission rates, branching ratios, and lifetimes of Tm3+ are calculated to evaluate the spectroscopic properties of Tm3+ in LAG glass. The infrared emission properties of the samples are investigated and the results show that the 1.8 μm emission can be greatly enhanced by adding proper amount of Yb3+ under the excitation of 980 nm. The energy transfer processes of Yb3+–Yb3+ and Yb3+–Tm3+ are analyzed, and the results show that Yb3+ ions can transfer their energy to Tm3+ ions with high efficiency and large energy transfer coefficient.