The dehydratation process of layered lanthanide silicates K3[LnSi3O8(OH)2], Ln = Y, Eu, Tb, and Er, and the structural characterization of the obtained small-pore framework K3LnSi3O9, Ln = Y, Eu, Tb, and Er solids, named AV-23, have been reported. The structure of AV-23 has been solved by single-crystal X-ray diffraction (XRD) methods and further characterized by chemical analysis, thermogravimetry, scanning electron microscopy, and 29Si MAS NMR. The photoluminescence (PL), radiance, and lifetime values of AV-23 have been studied and compared with those of AV-22. Both materials have a similar chemical makeup and structures sharing analogous building blocks, hence providing a unique opportunity for rationalizing the evolution of the PL properties of lanthanide silicates across dimensionality. Although Tb-AV-23 contains a single crystallographic Tb(3+) site, PL spectroscopy indicates the presence of Ln(3+) centers in regular framework positions and in defect regions. PL evidence suggests that Eu-AV-23 contains a third type of Ln(3+) environment, namely, Eu(3+) ions replacing K(+) ions in the micropores. The radiance values of the Tb-AV-22 and Tb-AV-23 samples are of the same order of magnitude as those of standard Tb(3+) green phosphors. For the samples K3(Y1-aEraSi3O9), a = 0.005-1, efficient emission and larger 4I13/2 lifetimes (ca. 7 ms) are detected for low Er(3+) content, indicating that the Er(3+)-Er(3+) interactions become significant as the Er(3)+ content increases.