Stimulated emission from flashlamp-pumped coumarin- and phthalimide-based biphosphors

Investigations were made of the lasing properties of two new coumarin- and phthalimide-based biphosphors excited by radiation having a broad spectral composition. In the first biphosphor the donor was para-terphenyl and the acceptor was coumarin 120. Both these substances lased efficiently when used separately. When the concentration was optimal, the lasing energy of the first biphosphor was 25–30% higher than that of coumarin 120 and several tens of times higher than the lasing energy of an equimolar mixture. In the second biphosphor the donor was stilbene with a low fluorescence quantum efficiency, but capable of quenching the triplet states of the acceptor, which was phenyl phthalimide that lased weakly with a high threshold. The lasing energy of the second biphosphor was five times higher than that of phenyl phthalimide and considerably higher than that of the mixture. The improvement in the lasing properties of the second biphosphor can be attributed to intramolecular quenching of acceptor triplets by the donor.