The emergence of single-component organic dual light emitters holds great promise for white light-emitting diodes (WLEDs) and biological detection due to the involvement of broad emission covering visible spectrum. Here we show experimental studies on dual emission of carbazole-quinoline conjugate (CQ) that exhibits both thermally activated delayed fluorescence (TADF) via reverse intersystem crossing (r ISC) from the higher-lying triplet state ( T) to the singlet state ( S) and room-temperature phosphorescence (RTP) from the lowest triplet state ( T) due to low energy gap between T and S, and energetic proximity of T with T. We found in thermal effect that the intensity of the dual features is enhanced with increasing temperatures up to 100 °C, which can be explained by a thermal-induced structural change (TISC) mechanism that compensates the emission losses due to nonradiative transitions at elevated temperatures. This property, in addition to its enhanced TADF and phosphorescence decay rates (∼10 sand 10 s) at 100 °C, would have great promise for high-efficiency LEDs.

Purely organic biluminescent materials are of great interest due to the involvement of both singlet and long-lived triplet emissions, which have been rarely reported in bioimaging and organic light-emitting diodes. We show two molecules 3,4,5,6-tetraphenyloxy-phthalonitrile (POP) and 3,4,5,6-tetrakis- p-tolyloxy-phthalonitrile (TOP), in which POP was found to exhibit fluorescence and persistent room-temperature green phosphorescence (pRTGP) in the amorphous powder and crystal states. Both POP and TOP show aggregation-induced emission in a tetrahydrofuran-water mixture. We found in single-crystal X-ray analysis that intra- and intermolecular lp(O)···π interactions along with π(C = C)···π(C≡N), hydrogen bond (H-B), and C-H···π interactions induce a head-to-tail slipped-stack arrangement in POP. In addition, the X-ray structure of TOP with a slipped-stack arrangement induced by only π(C═C)···π(C≡N) and H-B interactions shows dim afterglow only in crystals. These indicate that more noncovalent interactions found in POP may reinforce relatively efficient intersystem crossing that leads to pRTGP. Given the unique green afterglow feature in amorphous powder of POP, document security protection application is achievable.

Pure organic white light emitters with an afterglow (AG) feature have unique advantages and various potential applications. However, the studies of single-component organic white light emitters with AG and visible light excitation (VLE)-dependent efficient room-temperature phosphorescence (RTP) features remain a challenging area of research in photophysics. Herein, we synthesize three terephthalonitriles in which 2,3,5,6-positions are covalently attached to 2-fluoro-phenoxy (TOF), 2-chloro-phenoxy (TOC), and 2-methoxy-phenoxy groups (TOM) to give twisted geometries. We observed that powder samples of both TOC and TOM show white light emission with CIE coordinates of (0.32, 0.38) and (0.26, 0.33), respectively, while TOM gives VLE-dependent efficient RTP under ambient conditions. In addition, both TOC and TOF exhibit a dim AG feature. Spectroscopic studies reveal that dual emission of these chromophores originates via radiative decay of monomeric excited states (singlet, triplet), dimer-like excited states (DLES) (singlet, triplet), and aggregated triplet states. Detailed spectroscopic and X-ray analyses reveal the signature of DLES that is formed via conformational reorganization of the phenoxy donors in the excited states. Single-crystal X-ray diffraction analysis shows that the multiple lp­(O)···π­(CN)/CC, Cl/F···π, and hydrogen-bonding interactions in the X-ray structures play a significant role in facilitating intersystem crossing, stabilizing multiple triplet states, and suppressing nonradiative decay, thereby triggering dim afterglow under ambient conditions. We found that TOC and TOF exhibit persistent RTP (PRTP) with lifetimes of 139 and 736 ms, respectively, when they are embedded in the polyvinyl alcohol matrix. Given the PRTP feature, invisible security ink application is developed. These results provide a guidance to design white light-emitting materials with afterglow and visible light-activated efficient RTP features.

Developing new photoluminescent (PL) materials with simultaneous room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) features is highly desirable for bio-imaging, security applications and sensors due to the involvement...

This paper presents the design and preliminary evaluation of small-pixel CdTe gamma ray detectors equipped with a hybrid pixel-waveform (HPWF) readout system for gamma ray imaging applications with additional discussion on CZT due to its similarity. The HPWF readout system utilizes a pixelated anode readout circuitry which is designed to only provide the pixel address. This readout circuitry works in coincidence with a high-speed digitizer to sample the cathode waveform which provides the energy, timing, and depth-of-interaction (DOI) information. This work focuses on the developed and experimentally evaluated prototype HPWF-CdTe detectors with a custom CMOS pixel-ASIC to readout small anode pixels of 350 μm in size, and a discrete waveform sampling circuitry to digitize the signal waveform induced on the large cathode. The intrinsic timing, energy, and spatial resolution were experimentally evaluated in this paper in conjunction with methods for depth of interaction (DOI) partitioning of the CdTe crystal. While the experimental studies discussed in this paper are primarily for evaluating HPWF detectors for small animal PET imaging, these detectors could find their applications for ultrahigh-resolution SPECT and other imaging modalities.