Efficient energy transfer in organic thin films—implications for organic lasers

We show that efficient nonradiative (Förster) energy transfer between solid films of two highly luminescent perylene dyes blended in a solid film can be used to control the amplified spontaneous emission (ASE) emitted from the films under pulsed optical excitation. Perylene orange, which acts as the donor, and perylene red, which is the acceptor, are doped into a host matrix of poly(methylmethacrylate) (PMMA). We report the ASE behavior as a function of acceptor concentration, and observe a sudden change in the spectral position of the ASE at an acceptor:donor concentration of 1:9 by weight. Below this concentration, emission is at 590 nm, which is characteristic of ASE from undoped perylene orange:PMMA blends, whereas films with higher acceptor concentrations produced ASE spectra centered at 620 nm, which is characteristic of perylene red:PMMA blends. In order to understand this behavior, the rate constant for energy transfer between the dyes was measured and found to be $5.0±0.2×1011 s−1 (mol/dm3)−1.$ We used this to deduce an upper limit for the stimulated emission rate of $4.9±0.2×108 s−1.$