[16a-Z18-1~7] 12.4 Organic light-emitting devices and organic transistors

▲ [16a-Z18-7] Triplet recycling for quasi-continuous-wave organic semiconductor lasers

〇(D)ADIKARIMUDIYANSELAGE CHATHURANGANIE SENEVIRATHNE^1,2, Seiya Yoshida^1,2, Morgan Auffray^1,2, Buddhika S. B. Karunathilaka^1,2, Kenichi Goushi^1,2, Atula S. D. Sandanayaka^1,2,3, Toshinori Matsushima^2,4, Chihaya Adachi^1,2,4 (1.OPERA, Kyushu Univ., 2.JST ERATO, 3.Sabaragamuwa Univ., 4.WPI-I2CNER, Kyushu Univ.)

Keywords:organic semiconductor, triplet recycling, quasi-continuous-wave

Organic semiconductor lasers are well known for its excellent performance in short-pulse photoexcitation. However, lasing under continuous-wave or long-pulse photoexcitation from organic semiconductors is challenging because of the accumulation of long-lived triplets which formed via intersystem crossing from radiative singlets. Subsequently, these triplets induce singlet-triplet annihilation (STA), resulting in low singlet density in a laser medium. Hence, lasing from organics stops immediately. So far to induce organic lasing under long-pulse photoexcitation, these detrimental triplets should be eliminated from the laser medium. Instead of eliminating the long-lived triplets, here we report an efficient recycle of these triplets via triplet scavenging and then triplet up-conversion using triplet-triplet annihilation (TTA) to generate more singlet excitons in the laser medium. An anthracene derivative of 9-(1-naphthalenyl)-10-(4-(2-naphthalenyl)phenyl)anthracene (NaNaP-A) and a laser dye of 4,4’-bis[4-(diphenylamino)styryl]biphenyl (BDAVBi) were used as the triplet recycling host and laser dye in our laser system. BDAVBi has a considerable overlap of its emission spectrum with a triplet absorption spectrum of NaNaP-A which normally induces strong STA. However, a deep triplet state (1.5 eV) of NaNaP-A scavenges the long-lived triplets formed on BDAVBi via intersystem crossing and its long triplet lifetime (369 µs) facilitates TTA to upconvert the scavenged triplets into the singlets. As the STA process is suppressed with the triplet recycling process, our laser system could operate under long-pulse photoexcitation of up to 10 ms. Finally, the triplet recycling mechanism was further confirmed by transient electroluminescence and photoluminescence.