The hydrothermal synthesis and structural characterization of layered lanthanide silicates, K-3[M(1-a)Ln(a)Si(3)O(8)(OH)(2)] (M = Y3+, Tb3+; Ln = Eu3+, Er3+, Tb3+, and Gd3+), named AV-22 materials, are reported. The structure of these solids was elucidated by single-crystal (1180 K) and powder X-ray diffraction and further characterized by chemical analysis, thermogravimetry, scanning electron microscopy, Si-29 MAS NMR, and photoluminescence spectroscopy. The Er-AV-22 material is a room-temperature infrared phosphor, while Tb- and Eu-AV-22 are visible emitters with output efficiencies comparable to standards used in commercial lamps. The structure of these materials allows the inclusion of a second (or even a third) type of Ln(3+) ion in the framework and, therefore, the fine-tuning of their photoluminescent properties. For the mixed Tb3+/Eu3+ materials, evidence has been found of the inclusion of Eu3+ ions in the interlayer space by replacing K+ ions, further allowing the activation of Tb3+-to-Eu3+ energy transfer mechanisms. The occurrence probability of such mechanisms ranges from 0.62 (a = 0.05) to 1.20 ms(-1) (a = 0.1) with a high energy transfer efficiency (0.73 and 0.84, respectively).