We study the energies and optical spectra of excitons in twisted bilayers of anisotropic van der Waals semiconductors exhibiting moiré patterns, taking phosphorene as a case study. Leveraging the scale separation between the moiré length scale and the exciton Bohr radii, we introduce a continuous model for Wannier excitons that incorporates the spatial variation of their binding energies. Our calculations reveal a dimensionality crossover for the exciton states, driven by the combined dispersion and moiré potential anisotropies, from quantum dot lattices at twist angles $\theta <{\theta }_{*}$, to quantum wire arrays at $\theta >{\theta }_{*}$, with crossover angle ${\theta }_{*}=4^{\circ }$. We identify clear signatures of this dimensionality crossover in the twist angle dependence of the excitonic absorption spectra, which allows experimental verification of our theoretical results through standard optical measurements. Our results establish two-dimensional anisotropic moiré semiconductors as versatile solid-state platforms for exploring bosonic correlations across different dimensionalities.

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• Excitons
• Phosphorene
• Twisted heterostructures