Electroluminescent devices

A fluorescent electronic device comprising a sensitizer and a fluorescent emitter, wherein the sensitizer is a phosphorescent compound and wherein at least one of the two following conditions (I) or (II) must be satisfied:

• S1K(FE)−S1K(S)≥X (I)
• S1max(FE)−S1max(S)≥Y (II)
• where the parameters used are as follows:
• X, Y are each −0.5 eV
• S1K(FE) is the energy of the first excited singlet state of the fluorescent emitter which is ascertained from the edge of the first maximum on the short-wavelength side of the normalized photoluminescence spectrum of the fluorescent emitter;
• S1K(S) is the energy of the first excited state of the sensitizer which is ascertained from the edge of the first maximum on the short-wavelength side of the normalized photoluminescence spectrum of the sensitizer;
• S1max(FE) is the energy of the first excited singlet state of the fluorescent emitter which is ascertained from the location of the first maximum at short wavelengths of the photoluminescence spectrum of the fluorescent emitter;
• S1max(S) is the energy of the first excited state of the sensitizer which is ascertained from the location of the first maximum at short wavelengths of the photoluminescence spectrum of the sensitizer;
• wherein the photoluminescence spectra of the sensitizer and of the fluorescent emitter are determined from solution at a concentration of 1 mg in 100 ml of toluene at room temperature.