FRET-assisted laser emission in colloidal suspensions of dye-doped latex nanoparticles

The use of commercial long-wavelength(>650 nm) laser dyes in many biophotonic applications has several important limitations, including low absorption at the standard pump wavelength (532 nm) and poor photostability. Here, we demonstrate that the use of Forster type (FRET) energy transfer can overcome these problems to enable efficient, stable near-infrared lasing in a colloidal suspension of latex nanoparticles containing a mixture of Rhodamine 6G and Nile Blue dyes. Experimental and theoretical analyses of the photophysics suggest that the dominant energy transfer mechanism is Forster type via dipole-dipole coupling, and also reveal an unexpected core/shell morphology in the dye-doped nanoparticles. FRET-assisted incoherent random lasing is also demonstrated in solid samples obtained by evaporation of colloidal suspensions.