An Organic Laser Dye having a Small Singlet‐Triplet Energy Gap Makes the Selection of a Host Material Easier
Buddhika S. B. Karunathilaka, Umamahesh Balijapalli, Chathuranganie A. M. Senevirathne, Yu Esaki, Kenichi Goushi, Toshinori Matsushima, Atula S. D. Sandanayaka, Chihaya Adachi
Abstract
Abstract Quenching of singlets by long‐lived triplets is a serious issue for lasing from organic laser dyes, especially under long pulse excitation. As a strategy to scavenge or manage unnecessary triplets, an organic laser dye is dispersed into a host material having high singlet and low triplet energy levels [a large singlet‐triplet energy gap (Δ E ST )]. However, finding such a host material having a triplet scavenging capability is limited. In this study, an organic laser dye, 2,6‐dicyano‐1,1‐diphenyl‐λ 5 σ 4 ‐phosphinine (DCNP), having a small Δ E ST of ≈0.44 eV is synthesized, and thus 4‐4′‐bis[( N ‐carbazole)styryl] biphenyl (BSBCz) can be employed as a triplet scavenging host, i.e., the triplets formed on DCNP are easily transferred to BSBCz. A 1 wt%‐DCNP‐doped BSBCz film is formed on a mixed‐order distributed feedback grating, showing lasing with a low threshold value of ≈0.86 µJ cm −2 and a full‐width‐at‐half‐maximum value of ≈0.5 nm. Because of the suppressed singlet‐triplet annihilation, DCNP‐based laser devices operating under a continuous‐wave regime, with a low threshold of 72 W cm −2 and a long laser half‐lifetime of ≈3 min, are demonstrated. These results indicate a possibility of the wider selection of host materials, easing a material design strategy of fabricating high‐performance laser devices in future.