The study of Lamb shift plays a unique role in quantum electrodynamics because it provides an excellent test of the theory on photonic crystals (PCs). In this Letter, we present the first observation of large Lamb shift in the ${\mathrm{YBO}}_3\text{:}{\mathrm{Eu}}^{3+}$ inverse opals fabricated by the polystyrene templating method. In addition, it is very interesting to observe that the luminescent dynamics of ${\mathrm{Eu}}^{3+}$ decayed with a faster power law ( $t^{-3}$ ), followed by a slower exponential process due to the coexistence of the diffusion field and the propagating field in the PCs.