The shape and fine structure of lines due to Tm3+
f −f electronic transitions in multifunctional Y3Al5O12 garnet crystals have been studied by high-resolution spectroscopy. The observed inhomogeneously broadened lines have a Lorentzian shape, suggesting that point defects make a predominant contribution to the inhomogeneous broadening. Moreover, YAl antisite defects, which are formed during high-temperature melt growth, produce spectral satellites near the main lines.