We report on the long-range dipole-dipole Forster energy transfer between a fluorescent dye and a phosphorescent dopant in solid thin films. For our study we used 4,4'-N,N'-dicarbazole-biphenyl as a host and the organometallic complex fac tris(2-phenylpyridine) iridium(III) as a guest. By studying the photoluminescence efficiency of films with various host and guest concentrations and by comparing these results with those obtained from a numerical model, we determine a Forster radius of R(0)similar to3 nm.