Stimulated Singlet – Triplet Transitions in Organic Phosphors

Abstract

MORANTZ et al.¹ have reported that stimulated emission may be observed from the triplet states of organic phosphors. The emission was characterized by a regular series of spikes of intensity implying an oscillatory condition due to the amplification of the stimulated emission as in similar experiments on ruby. Workers in other laboratories, including our own, have failed to detect this effect. We have, however, succeeded in producing the triplet state of such a compound by the reverse process of direct singlet–triplet absorption using a typical flash photolysis apparatus. This is interesting in its own right as it paves the way for studies of triplet states in the absence of excited singlet states, something which hitherto had not been thought possible. Furthermore, the small fraction of molecules excited in this way is in agreement with calculations which suggest that a prohibitively high inversion population density is required to obtain oscillation in a resonant cavity with such compounds using flashes of energy less than 1,000 joules. Experience suggests that even with a 100-fold increase in flash intensity, such concentrations would be difficult to realize.