Photoluminescent Layered Lanthanide Silicates

The hydrothermal synthesis and structural characterization of layered lanthanide silicates,
K3[M1-aLnaSi3O8(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 (180 K) and powder X-ray diffraction
and further characterized by chemical analysis, thermogravimetry, scanning electron microscopy, 29Si 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 Ln3+ 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).