Near-Infrared Ratiometric Luminescent Thermometer Based on a New Lanthanide Silicate

A new lanthanide silicate system, Na2K[Ln(3)Si(6)O(18)] (Ln=Lu, Yb/ Er, Lu/Eu, or Lu/Yb/Er), comprising microcrystals embedded in an amorphous siliceous matrix, obtained by sintering at 1373K a Na3K[Ln(2)Si(6)O(17)]center dot 3H(2)O nano-crystalline precursor, is reported. The crystal structure of these lanthanide silicates was solved from high-resolution synchrotron power X-ray diffraction data collected at 110K, and further supported by Si-29 MAS NMR and Eu3+ luminescence. The materials crystallize in the P-(1) over bar triclinic centrosymmetric space group, exhibiting a dense framework consisting of hexameric [Si6O18](12-) cyclosilicate units, and chains of two distinct {LnO(6)} octahedra. Na2K[(Lu0.75Yb0.20Er0.05)(3)Si6O18] is the first example of a lanthanide silicate operative as a near-infrared ratiometric luminescent thermometer, with good sensitivity at cryogenic temperatures (<100K). Upon excitation at 903nm, the ratio between the F-2(7/2) -> F-2(5/2) (Yb3+) and I-4(13/2) -> I-4(15/2) (Er3+) emissions was used for sensing temperature in the 12-450K range, reaching a maximum thermal sensitivity of 2.6%K-1 at 26.8K.