Characterization of Rhodamine 6G Aggregates Intercalated in Solid Thin Films of Laponite Clay. 2 Fluorescence Spectroscopy

The photoluminescence response of Rhodamine 6G (R6G) laser dye intercalated into solid thin films of Laponite (Lap) clay is studied as a function of dye loading. Fluorescence spectroscopy (steady-state and time-resolved techniques) was used to characterize the R6G species adsorbed into the solid films. For very diluted R6G loadings (≤0.1% CEC, i.e., the percentage of the total cation exchange capacity of Lap) the fluorescence properties of R6G monomer were characterized, which presents an emission band centered at 548 nm, an average lifetime of 4.2 ns, and a fluorescence efficiency higher than that of the R6G monomer in liquid solution. By increasing the loading, dye molecules tend to self-aggregate, and different dimers are formed in moderate dye concentrations (in the 1−25% CEC range): oblique head-to tail J-type dimers, with weak emission bands at around 575 nm; and sandwich H-type dimers, as efficient quenchers of the fluorescent emission. Higher-order aggregates of R6G in Lap films are formed in high loading samples (>40% CEC), with a reminiscent fluorescence band at around 600 nm.