Abstract—Values of φT, the quantum yield of triplet state production of 9‐phenylanthracene, have been determined in four different solvents by measuring the effects which ‘heavy atom quenchers’ have on the fluorescence intensity and the triplet state absorption of the solute. A variety of quenchers have been used including organic and inorganic halides and the rare gas, Xenon. There is a converse solvent dependence of φFand φT, and for each of the four solvents used φF+φThas been found to be unity within experi