NOVELTY - Composition comprises: an organic molecule for the emission of light, which exhibits delta E(S1-T1)-value between the lowest excited singlet (S1) and the underlying triplet state (T1) of less than 2500 cm-1; and an optically inert atom or an optically inert molecule for reducing an inter-system crossing time constant of the organic molecule to less than 10-6 second.    USE - The composition is useful in an emitter layer in an optoelectronic device preferably an organic light emitting diode, a light-emitting electrochemical cell, an organic light emitting diode sensor, preferably not hermetically sealed to the outside gas, a vapor sensor, an optical temperature sensor, an organic solar cell, an organic field effect transistor, an organic laser, an organic diode, an organic photodiode or a down conversion system, where the amount of the composition in the emitter layer is 2-100 wt.%, preferably 60-30 wt.%, based on the total weight of the emitter layer (all claimed).    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) producing an optoelectronic device, comprising using the composition;    (2) reducing the emission lifetime or increasing the electroluminescent quantum yield using the organic molecule as the emitter in the optoelectronic device, comprising adding the optically inert atom or the molecule to the organic molecule so that the optically inert atom or molecule interacts with the organic molecule, where the optically inert atom, the molecule or the parts of the optically inert molecule exhibits a spin-orbit coupling constant of greater than 1000 cm-1, preferably greater than 4000 cm-1;    (3) converting a triplet excitation energy of the organic molecule generated during the electroluminescence into a fluorescence energy, comprising interacting the organic molecule with the optically inert atom or the molecule, and converting the triplet excitation energy of the organic molecule over a singlet state of the organic molecule into fluorescent energy; and    (4) selecting the organic molecule with delta E(S1 - T1)-value between the lowest excited singlet (S1) and the underlying triplet state (T1) of less than 2500 cm-, preferably less than 1000 cm-1, comprising determining delta E(S1-T1)-value of the organic molecules using an ab initio molecular calculation, or by measuring the temperature dependence of fluorescence- and phosphorescence intensity, and determining the organic molecule, whose delta E(S1-T1)-value between the lowest excited singlet (S1) and the underlying triplet state (T1) is less than 2500 cm-, preferably less than 1000 cm-1.    DESCRIPTION OF DRAWING(S) - The figure 1 shows a schematic representation of the organic light emitting diode (Drawing includes non-English language text).