Stable emission in glass Lead halide perovskites can exhibit bright, narrow band photoluminescence but have stability issues related to formation of inactive phases and the loss of lead ions. Hou et al . show that the black, photoactive phase of cesium lead iodide can be stabilized by forming a composite with a glassy phase of a metal-organic framework through liquid-phase sintering. The photoluminescence is at least two orders of magnitude greater than that of the pure perovskite. The glass stabilizes the perovskite under high laser excitation, and about 80% of the photoluminescence was maintained after 10,000 hours of water immersion. —PDS

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Triplet energy harvesting via either thermally activated delayed fluorescence (TADF) or room-temperature phosphorescence (RTP) from pure organic systems has attracted great attention in the field of organic light-emitting diodes, sensing, and bioimaging. However, the realization of dual electroluminescence via TADF and RTP in single molecules remains elusive. Herein, we report two phenoxazine-quinoline conjugates (DPQ and DPQM) in which two phenoxazine donors are covalently attached to the 6,8-positions of 2,4-diphenylquinoline and/or 7-methyl-2,4-diphenylquinoline acceptors. Experimental and quantum chemistry calculations combining reference compounds ( o-PQP, p-PQP, Phox, and QPP) reveal that both conjugates show TADF (with different rate constants of reverse intersystem crossing, k rISC = 0.43–1.30 × 106 s–1) via reverse intersystem crossing from the charge transfer triplet (3CT) to singlet (1CT) states mediated by vibronic coupling among 1CT, local triplet (3LE), and 3CT states due to close energy gaps. Further, RTP with quantum yields (ϕP) of ca. 21–24% features was also observed due to the radiative decay of 3LE states. Phosphorescence measurements of DPQM at low temperatures (T = 77, 10 K) ensure a distinct zero-field splitting of T 1(CT) into substates. Both compounds showed dual electroluminescence with external quantum efficiencies of ca. 11–12% due to the efficient triplet harvesting from both TADF and RTP channels.

Recent studies have demonstrated that in thermally activated delayed fluorescence (TADF) materials, efficient reverse intersystem crossing occurs from non-radiative triplet states to radiative singlet states due to a small singlet-triplet energy gap. This reverse intersystem crossing significantly influences exciton annihilation processes and external quantum efficiency roll-off in TADF based organic light-emitting diodes (OLEDs). In this work, a comprehensive exciton quenching model is developed for a TADF system to determine singlet-singlet, singlet-triplet, and triplet-triplet annihilation rate constants. A well-known TADF molecule, 3-(9,9-dimethylacridin-10(9H)-yl)-9H-xanthen-9-one (ACRXTN), was studied under intensity-dependent optical and electrical pulse excitation. Our model shows singlet-singlet annihilation dominates under optically excited decays, whereas singlet-triplet annihilation and triplet-triplet annihilation have strong contribution in electroluminescence decays under electrical pulse excitation. Furthermore, the efficiency roll-off characteristics of ACRXTN OLEDs at steady state was investigated through simulation. Finally, singlet and triplet diffusion length were calculated from annihilation rate constants.

The search for new classes of efficient electroluminescent organic laser dyes with low amplified spontaneous emission (ASE) threshold (E th) and low optical losses is crucial toward the realization of organic injection lasers. In this work, we report in-depth studies of an organic semiconducting laser dye, benzo­[d]­thiazol-2-yl)-5-(9H-carbazol-9-yl)­phenol (HBT-Cz), and compare the photophysical study with its parent HBT dye. While HBT is not laser-active in solution, the carbazole derivatized dye (i.e., HBT-Cz) showed a low solution ASE threshold of 21 mJ/cm2, which is comparable to a common high-performing commercial laser dye, Rhodamine 6G (Rh-6G). HBT-Cz also exhibited a low film ASE threshold of 2.4 μJ/cm2 with a low optical loss coefficient of 1.5 cm–1, which is the lowest waveguide loss coefficient reported for solution-processed organic semiconductors. Organic light-emitting diodes based on this material showed a high maximum EQE of 1.9%, which is close to the theoretical EQE limit of the emitter, and high brightness of >2,300 cd/m2. Further insights into the lasing properties of the material were provided by steady state UV–visible spectroscopy, and transient absorption spectroscopy, shedding light on excited-state species absorption. To the best of our knowledge, this is the first report of a solution-processable organic small molecular dye, exhibiting a low ASE threshold and lowest optical loss coefficient, coupled with efficient electroluminescence.